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United States Patent5930493
Ottesen , ; et al.July 27, 1999
Title
Multimedia server system and method for communicating multimedia information
Abstract
A multimedia server system and a method for communicating multimedia programming to distantly situated media control systems are disclosed. The multimedia server system includes a mass storage library for storing a plurality of multimedia programs. A multimedia program is coded in accordance with a predetermined compression standard and stored in a compressed digital format as sequentially ordered discrete program segments in the mass storage library, with each of program segments being representative of a unique portion of the multimedia program. A video parser organizes the sequentially ordered program segments of a multimedia program into a custom ordered series of program segments preferably including non-sequentially and sequentially ordered program segments in accordance with configuration parameters associated with the configuration and presentation control features of a media control system requesting the multimedia program. Concurrent transmission of a plurality of custom ordered series of program segments to a corresponding plurality of distantly located media control systems is facilitated by an asynchronous transfer mode distribution switch. The custom ordered series of program segments are processed by a local media control system to provide for the sequential presentation of the program segments on a local display and for providing local VCR-type control functions.
Inventors:Ottesen; Hal Hjalmar (Rochester, MN), Smith; Gordon J.  (Rochester, MN), VanLeeuwen; George Willard  (Rochester, MN)
Assignee:International Business Machines Corporation (Armonk, NY)
Appl. No.:472506
Filed:June 7, 1995
Current U.S. Class:725/92 725/93 725/99 
Current International Class:H04N 7/173 (20060101)
Field of Search:395/500,800 364/514R 348/7,467
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Primary Examiner: Teska; Kevin J.
Assistant Examiner: Siek; Vuthe
Attorney, Agent or Firm:Hollingsworth; Mark A. Merchant, Gould, Smith Edell, Welter & Schmidt Xu; Min S.
Parent Case Text


RELATED INVENTIONS

The present invention is related to:

co-pending U.S. patent application Ser. No. 08/288,525, filed on Aug. 8, 1994, which is entitled "Apparatus and Method for Providing Multimedia Data;"

co-pending U.S. patent application Ser. No. 08/488,329, filed on Jun. 7, 1995, which is entitled "Media-on-Demand Communication Method and Apparatus;"

co-pending U.S. patent application Ser. No. 08/488,328, filed on Jun. 7, 1995, which is entitled "Multimedia Control System and Method for Controlling Multimedia Program Presentation;" and

co-pending U.S. patent application Ser. No. 08/472,506, filed on Jun. 7, 1995, which is entitled "Multimedia Direct Access Storage Device and Formatting Method," all of which are assigned to the assignee of the present invention.
Claims

We claim:
1. A server system for communicating multimedia programming to a distantly situated local media control system over a communication channel, the server system comprising:
a mass storage library for storing a plurality of multimedia programs, the multimedia programs being segmented into source program segments, and each of the source program segments representing a multimedia program portion;
an organizing unit that arranges the source program segments of a selected multimedia program into a custom ordered series of source program segments including non-sequentially ordered source program segments and sequentially ordered source program segments;
a transmission unit that transmits the source program segments of the custom ordered series to the communication channel;
a server controller that communicates with the local media control system and receives a configuration signal from the local media control system over the communication channel, the configuration signal being representative of configuration parameters associated with the local media control system; and
the organizing unit, in response to the configuration signal, organizing the source program segments into the custom ordered series of source program segments in accordance with the configuration parameters.

2. A system as claimed in claim 1, wherein:
the server system further comprises a coder that codes the source program segments defining the plurality of multimedia program stored in the mass storage library in accordance with a predetermined coding standard.

3. A system as claimed in claim 1, wherein the mass storage library includes either one of a digital storage device and a dynamic random access storage device for respectively storing the plurality of multimedia programs.

4. A system as claimed in claim 1, further comprising a segmenting unit that segments each of the plurality of multimedia programs into a corresponding series of sequentially ordered source program segments.

5. A system as claimed in claim 1, further comprising an indexing unit that associates a unique segment address with each of the source program segments.

6. A system as claimed in claim 1, further comprising a staging storage device, coupled to the organizing unit and the transmission unit that stores the custom ordered series of source program segments received from the organizing unit.

7. A system as claimed in claim 1, wherein the transmission unit transmits the source program segments arranged in packets to the communication channel, each of the packets comprising no greater than a predetermined maximum number of the source program segments.

8. A system as claimed in claim 1, wherein the transmission unit transmits the source program segments arranged in packets to the communication channel during transmission windows having a predetermined duration.

9. A system as claimed in claim 8, wherein the predetermined duration of the transmission windows is associated with the number of the source program segments arranged in the packets and the portion of the selected multimedia program represented by each of the source program segments arranged in the packets.

10. A system as claimed in claim 1, wherein the transmission unit comprises an asynchronous transmission mode switching unit that transmits a plurality of custom ordered series of source program segments representative of a corresponding plurality of multimedia programs asynchronously to a plurality of distantly situated local media control systems over the communication channel.

11. A server system for communicating multimedia programming to a distantly situated local media control system over a communication channel, the server system comprising:
a mass storage library for storing a plurality of multimedia programs each segmented into source program segments, each of the source program segments including a unique segment address and being representative of a portion of one of the plurality of multimedia programs;
an organizing device that arranges the unique segment addresses of source program segments associated with the one of the plurality of multimedia programs to produce a custom ordered series of source program segments;
a transmission device that transmits the custom ordered series of source program segments arranged in packets to the communication channel; and
wherein the organizing device arranges the unique segment addresses to produce a custom ordered series of source program segments including non-sequentially ordered source program segments.

12. A system as claimed in claim 11, further comprising a segmenting device that segments each of the plurality of multimedia programs into a corresponding series of sequentially ordered source program segments.

13. A system as claimed in claim 11, wherein the mass storage library includes either one of a digital storage device and a dynamic random access storage device for respectively storing the plurality of multimedia programs.

14. A system as claimed in claim 11, further comprising a staging storage device, coupled to the organizing device and the transmission device, for storing the custom ordered series of source program segments received from the organizing device.

15. A method for communicating a multimedia program from a remote multimedia server to a local media control system, the method comprising:
organizing sequentially ordered source program segments representative of the multimedia program into a custom ordered series of source program segments, the custom ordered series comprising non-sequentially ordered and sequentially ordered source program segments, and each program segment representing a unique portion of the multimedia program;
transmitting the source program segments of the custom ordered series to a communication channel; and
wherein the transmitting step includes the further step of transmitting the source program segments of the custom ordered series arranged in packets to the communication channel during transmission windows having a predetermined duration.

16. A method as claimed in claim 15, including the further step of segmenting the multimedia program into the sequentially ordered source program segments.

17. A method as claimed in claim 15, including the further step of selecting the multimedia program from a plurality of multimedia programs.

18. A method as claimed in claim 15, including the further step of coding the sequentially ordered source program segments in accordance with a predetermined coding standard.

19. A method as claimed in claim 15, wherein the predetermined duration of the transmission windows is associated with the number of source program segments arranged in the packets and the portion of the multimedia program represented by each of the source program segments arranged in the packets.

20. A method as claimed in claim 15, wherein the transmitting step includes the further step of transmitting the source program segments of the custom ordered series to the communication channel in accordance with an asynchronous transfer mode transmission methodology.
Description
FIELD OF THE INVENTION

The present invention relates generally to server-based storage and communication systems, and, more particularly, to a multimedia server system and method for communicating multimedia information.

BACKGROUND OF THE INVENTION

Advancements in communications technology and increased consumer sophistication have challenged the distributors of multimedia programming to provide the subscribing public with entertainment services more convenient and accessible than those traditionally made available over cable television and telephone systems. An improving communications infrastructure has resulted in a proliferation of pay-per-view media services in many of the larger broadcast markets. Most pay-per-view systems permit the consumer to choose from a relatively small number of motion picture selections for home viewing, with the selected programs generally being presented only at pre-scheduled viewing times.

A number of on-demand video services have been developed that permit the consumer to order desired programs for home viewing through the household telephone line. For example, U.S. Pat. No. 5,247,347, assigned to Bell Atlantic Network Services, discloses a sophisticated video-on-demand telephone service that provides consumer ordered video programming to a plurality of households through use of a public switched telephone network (PSTN). An extensive discussion regarding the inherent deficiencies of communicating video and other multimedia signals over standard bandwidth limited analog telephone lines is provided in the '347 patent.

The video-on-demand system disclosed in the '347 patent and other conventional telephony-based multimedia services fail to satisfactorily address the adverse impact to home communications during periods of prolonged program viewing. For example, a typical theatrical motion picture can tie up the household telephone line for over two hours. Further, such sophisticated telephony-based multimedia services generally require procurement of expensive communications and diagnostic equipment by the pay-per-view provider to ensure a reasonable level of signal quality and system reliability. These and other related operating expenses, however, are typically passed on to the consumer.

Importantly, conventional multimedia services fail to provide media presentation control features now expected by the sophisticated consumer after enjoying more than a decade of home entertainment through the use of a video cassette recorder (VCR). Functions such as fast forward, reverse, and pause, for example, are standard presentation control functions now provided by all or most home VCRs, and are typically effectuated by use of an infrared (IR) remote control handset. The limited transmission bandwidth of household telephone lines, as well as common cable television channels, generally precludes accommodation of full VCR-type control functionality when employed to support a conventional multimedia communication system adapted to provide on-demand service to a large number of subscribing customers.

In FIG. 1, for example, there is illustrated a generalized block diagram of a conventional pay-per-view communication service for providing video program distribution to a plurality of households over a public switched telephone network. Movies are typically stored on one or more media servers 10, each of which is multiplexed to the PSTN 16. A telephonic ordering system 14 is generally coupled to the PSTN 16, and provides a means for accepting a pay-per-view order from a customer or user 20
over the telephone. Upon verifying the account status of a user 20, the media server 10 typically transmits the ordered movie or program to a decoder box 22 coupled to the customer's telephone line 18. The transmitted program is continuously decoded by the decoder box 22 to provide continuous presentation of the selected program on the customer's television 24. Limitations in the transmission bandwidth of the telephone lines 18, as well as limitations in the switching capability of the PSTN 16, generally preclude the use of a PSTN 16 to support a media communication system that provides high quality, full-motion video signal transmission with full VCR-type control functionality. Such limitations similarly impact a conventional pay-per-view video communication service that utilizes cable television lines.

Other video communication systems, such as that disclosed in U.S. Pat. No. 4,949,187, provide a local disk storage system for storing a digitized multimedia program received from a central archive library. After establishing a telephonic link with the central server 10 over a PSTN telephone network, a selected digitized movie is downloaded in its entirety into the disk storage system incorporated into the terminal unit disclosed in the '187 patent. This and other home communication systems that employ disk storage systems to provide local storage of a selected multimedia program generally require downloading of the entire multimedia program prior to viewing the program on the subscriber's television.

Depending on the bandwidth of the telephone line and source transmission rate, the downloading procedure may delay viewing of a selected movie for an appreciable amount of time. Very-high capacity data storage systems are generally required to locally store an entire feature-length movie. Such local data storage systems must generally be configured to allocate several gigabytes of memory for storing a typical movie in a compressed form, and several hundred gigabytes of memory for storing a typical non-compressed movie.

The excessively large memory requirement of these and other conventional local data storage systems employed to store video programming in accordance with a conventional media communication methodology generally results in a commercial product that is prohibitively expensive for the average consumer. Also, such systems cannot provide instantaneous viewing of a selected multimedia program immediately upon receiving the transmission of the program signals from the server 10. Moreover, VCR-type control functionality can only be provided, if at all, after downloading the entire multimedia program onto the disk storage system.

There exists a need in the communications industry for a media-on-demand communication system that provides local VCR-type control over the presentation of a selected multimedia program at a minimal cost to the consumer. There exists a further need to provide a multimedia communication system that can efficiently distribute programming to a plurality of subscribing customers without requiring complex and typically expensive server processing hardware and software at the remote communication distribution center. The present invention fulfills these and other needs.

SUMMARY OF THE INVENTION

The present invention is a multimedia server system and a method for communicating multimedia programming to distantly situated media control systems. The multimedia server system includes a mass storage library for storing a plurality of multimedia programs. A multimedia program is coded in accordance with a predetermined compression standard and stored in a compressed digital format as sequentially ordered discrete program segments in the mass storage library, with each of program segments being representative of a unique portion of the multimedia program. A video parser organizes the sequentially ordered program segments of a multimedia program into a custom ordered series of program segments preferably including non-sequentially and sequentially ordered program segments in accordance with configuration parameters associated with the configuration and presentation control features of a media control system requesting the multimedia program. Concurrent transmission of a plurality of custom ordered series of program segments to a corresponding plurality of distantly located media control systems is facilitated by an asynchronous transfer mode distribution switch. The custom ordered series of program segments are processed by a local media control system to provide for the sequential presentation of the program segments on a local display and for providing local VCR-type control functions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional communication system for distributing selected video programs to a plurality of users;

FIG. 2 is a generalized block diagram of a novel multimedia communication system for distributing multimedia programs concurrently to a plurality of subscriber set-top control systems preferably on an on-demand, pay-per-view basis;

FIG. 3 is a generalized block diagram of a novel multimedia server for communicating a synchronous, asynchronous, or combined synchronous/asynchronous series of source program segments representative of a selected multimedia program to a plurality of subscriber set-top control systems preferably on an on-demand, pay-per-view basis;

FIG. 4 is a generalized block diagram of a mass storage library portion of a novel multimedia server;

FIG. 5 is an illustration of a partial series of synchronous compressed source program segments, with each discrete program segment being representative of a predetermined time portion of a multimedia program;

FIG. 6 is an illustration of a customized series of discrete source program segments including an asynchronous source program segment series portion followed by a synchronous source program segment series portion, with each discrete source program segment being representative of a predetermined time portion of a multimedia program;

FIG. 7 is an illustration of an initially synchronously ordered series of source program segments representative of a two-hour multimedia program arranged as a 60.times.120 matrix of 7,200 discrete one-second source program segments;

FIG. 8 is an illustration of 7,200 discrete one-second source program segments representative of a two-hour multimedia program arranged in a 20.times.360 customized matrix comprising two 10.times.360 sub-matrices or blocks, with each block containing 3,600 asynchronously ordered discrete one-second source program segments;

FIG. 9 is an illustration of 3,600 discrete two-second source program segments representative of a two-hour multimedia program arranged in a 20.times.180 customized matrix comprising four 5.times.180 sub-matrices or blocks, with each of the four blocks containing 900 asynchronously ordered discrete two-second compressed source program segments;

FIG. 10 is a depiction of the asynchronously ordered source video segments contained in the first twelve segment packets transmitted by a novel multimedia server during successive transmission windows;

FIG. 11 is a generalized block diagram of a novel intelligent set-top control system adapted to communicate with a remote multimedia server to facilitate asynchronous formatting of source program segments on a multimedia DASD received from the multimedia server preferably on an on-demand, pay-per-view basis;

FIG. 12 is a depiction of a novel presentation control window effectuated using a novel intelligent set-top control system for controlling a portion of a multimedia program presentation in a plurality of presentation modes, including forward, reverse, and pause modes;

FIG. 13 is an illustration of a novel multimedia direct access storage device of a set-top control system adapted for buffering a predetermined number of discrete source program segments representative of at least a portion of a multimedia program to provide full local VCR-type control of the buffered portion of the selected multimedia program;

FIG. 14 is an exaggerated side plan view of a novel multimedia direct access storage device of a set-top control system including a plurality of data storage disks adapted for buffering discrete source program segments representative of at least a portion of a multimedia program;

FIG. 15 is an illustration of a novel data storage architecture for buffering synchronously and asynchronously ordered discrete source program segments on an outwardly spiralling data track disposed on an upper surface of a data storage disk;

FIG. 16 is an illustration of a novel data storage architecture for buffering synchronously and asynchronously ordered discrete source program segments on an inwardly spiralling data track disposed on a lower surface of a data storage disk;

FIG. 17 is an illustration of the first twenty asynchronously ordered source program segments defining a twenty second presentation control window buffer to be distributed on a lower and an upper surface of a data storage disk, with each discrete source program segment being representative of a one-second time portion of a multimedia program;

FIG. 18 is a depiction of twenty data storage locations defining a twenty second presentation control window disposed on a lower and an upper surface of a data storage disk, and a novel method for writing and reading discrete source program segments to and from the ten storage locations disposed on each of the lower and upper disk surfaces;

FIG. 19 is a composite illustration of a lower surface of a data storage disk superimposed along side of an upper surface of the data storage disk, with ten data storage locations disposed on each of the lower and upper disk surfaces for buffering at any one time twenty discrete source program segments comprising a twenty second presentation control window buffer in accordance with a novel formatting methodology;

FIG. 20 is a depiction of forty data storage locations disposed on a lower and an upper surface of a data storage disk defining a forty second presentation control window, and a novel method for writing and reading discrete source program segments to and from the ten storage locations organized into two segment blocks disposed on each of the lower and upper disk surfaces;

FIGS. 21-22 are flow charts depicting general processing steps performed by a novel multimedia server when communicating with a subscriber's set-top control system to provide on-demand transmission of source program segments representative of a multimedia program in accordance with configuration parameters associated with the configuration of a presentation control window buffer provided on a novel multimedia direct access storage device of the subscriber's set-top control system;

FIG. 23 is a flow chart depicting general processing steps performed by a novel intelligent set-top control system when communicating with a remote multimedia server to receive on-demand transmission of source program segments representative of a selected multimedia program in accordance with configuration parameters associated with the configuration of a presentation control window buffer provided on a novel multimedia direct access storage device of the set-top control system;

FIGS. 24-25 are flow charts depicting general processing steps performed by a novel intelligent set-top control system when writing a custom ordered series of discrete source program segments representative of a portion of a selected multimedia program to a presentation control window buffer provided on a novel multimedia direct access storage device, and when reading the discrete source program segments as a sequentially ordered series of discrete local program segments from the direct access storage device in accordance with a novel update-in-place formatting methodology; and

FIG. 26 is a flow chart depicting general processing steps associated with effectuating a spiral-and-hold operation of a novel multimedia direct access storage device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention, as previously indicated, relates to a multimedia server system and method for communicating multimedia information over a communication channel to distantly located media control systems, preferably on an on-demand, pay-per-view basis. The present application describes the entire multimedia communication system and process for providing multimedia program distribution from a remote multimedia server system to a plurality of distantly located set-top control systems. As such, there are described in the present application various features and functions of the multimedia communication system which are not the subject of the presently claimed subject matter, but are the subject of inventions claimed in co-pending applications filed concurrently with this application. The description of these features and functions are included in the present application for purposes of completeness, and to permit a full appreciation of the advantages and features of an multimedia set-top control system as disclosed herein.

Multimedia Communication System

Referring now to the drawings, and more particularly to FIG. 2, there is shown a system block diagram of a multimedia communication system employing a novel multimedia server 30 configured to communicate multimedia programs to a plurality of set-top control systems 62 concurrently over a communication channel 44. In one embodiment, the multimedia server 30 transmits a video program or other visual or audio presentation as a customized series of compressed digital source program segments to a subscribing customer's set-top control system 62 on an on-demand, pay-per-view basis. The program segments may be representative of video, animation, photographic, audio, textual, graphical, and other types information. A direct access storage device (DASD) is preferably coupled to the local set-top control system 62 for buffering a portion or all of the multimedia program received from the multimedia server 30.

A novel DASD formatting methodology is employed to buffer the customized series of compressed digital source program segments representative of a portion of the multimedia program to provide a subscriber with local VCR-type control of the presentation of the multimedia program portion buffered on the DASD, including presentation control functions such as fast forward, reverse, and pause. The multimedia program may, for example, be transmitted from the local set-top control system 62 to a subscriber's television 24, home stereo, or computer system by use of a standard household transmission line or pair of infrared transceivers. In one embodiment, the multimedia server 30 customizes the order of the source program segments in response to formatting and configuration parameters associated with the configuration and control functions of a subscriber's unique local set-top control system 62.

The novel formatting methodology provides for a significant decrease in the complexity and cost of operating and maintaining a central multimedia server system 30 adapted for distributing media-on-demand programming to a plurality of set-top control systems 62. It is noted that a set-top control system 62 may be located at a household, a business location, such as a restaurant or bar, or other private or public location. VCR-type presentation control functionality, including rewind, fast forward, pause, and other presentation modes, are locally coordinated directly by the set-top control system 62. By providing local control over the presentation of a multimedia program, the central multimedia server 30 need not be configured to effectuate VCR-type control functions typically desired by the subscribing customer.

Those skilled in the art will readily appreciate the significant difficulty of simultaneously servicing VCR-type presentation control function requests at a central media distribution site during the communication of user-selected programs transmitted concurrently to a plurality of customers on an on-demand, real-time basis. Providing the subscribing customer local control of a media presentation directly through the set-top control system 62 provides for a significant decrease in the bandwidth of the communication channel 44 and the amount of multimedia server 30 processing overhead that would otherwise be required to service VCR-type presentation control function requests from a plurality of pay-per-view customers.

A user of the set-top control system 62 preferably communicates with the multimedia server 62 over an existing communication channel 44, such as a cable television connection, for example. It is understood that a plurality of subscribing customers can concurrently communicate with the multimedia server 30 by use of the set-top control system 62, which may be situated proximate to or remotely from a television 24 or entertainment center within the subscribing customer's home or business establishment. A communications interface preferably couples the set-top control system 62 to a cable line or other communication line interfacing with the communication channel 44. The communications interface preferably includes a transceiver capable of both receiving and transmitting multimedia information, control, and other electrical signals communicated over the communication channel 44. Alternatively, the communications interface may include a separate receiver and transmitter for effectuating communication over the communication channel 44.

The multimedia information transmitted from the multimedia server 30 to a plurality of set-top control systems 62 is preferably transmitted in a digitally compressed format. A compression algorithm standard suitable for use by the novel media-on-demand communication system is one developed by the Moving Pictures Experts Group, and is generally referred to as an MPEG coding standard. The MPEG-1 standard (ISO/IEC IS 11172-1), for example, defines a format for compressed digital video which supports data rates of approximately 1.2 to 1.5 megabits per second (Mbps), resolutions of about 352 pixels (picture elements) horizontally to about 288 lines vertically, picture rates of about 24 to 30 pictures per second, and several VCR-like viewing functions, such as normal forward, play, slow forward, fast forward, fast reverse, and freeze. MPEG-1 coding provides compression ratios typically on the order of 100:1 to 150:1.

A new developing MPEG standard, referred to in the art as MPEG-2 (ISO/IEC IS 11172-2), is expected to support data rates on the order of approximately 2 to 15 Mbps over cable, satellite, and other broadcast channels. In addition to a video signal stream and an audio signal stream, MPEG-2 specifies an associated data signal stream that, together with the video and audio signal streams, comprise the multiplexed program bitstream. MPEG-2 will additionally support both non-interlaced and interlaced video signal formats, increased image quality over that provided by MPEG-1, multiple picture aspect ratios, and a number of other advanced features, including features to support High Definition Television (HDTV). It is noted that the MPEG-1
audio compression standard (ISO/IEC IS 11172-3) and developing MPEG-2 audio compression standard set forth audio compression specifications that are suitable for coding audio programs processed by the multimedia sever 30. It is to be understood that coding standards other than those conforming to one or more of the above-described MPEG standards may be employed to facilitate communication of video, audio, and other multimedia program signals between the multimedia server 30 and a plurality of customer set-top control systems 62 without departing from the scope and spirit of the present invention. For example, program signals transmitted over the communication channel 44 may be of a format other than a compressed digital format.

For purposes of explanation, the advantages and features of the disclosed media-on-demand communication method and apparatus will be discussed generally with reference to full-motion video. Full-motion video is useful for this purpose since video is generally a composite media comprising both video and audio components, and may also include other information components, such as subtitle or hearing-impaired information. Also, coding of full-motion video in accordance with an MPEG specification produces a multiplexed program signal stream that is well-suited for illustrating the advantages of the novel media-on-demand communication method and apparatus. It is to be understood that the references hereinbelow to video media are for purposes of explanation only, and do not represent limitations on the type and nature of multimedia programs and information stored on and processed by the multimedia server 30.

Multimedia Server

Turning now to FIGS. 3-4, there is illustrated an embodiment of a novel multimedia server 30 for storing and processing a variety of multimedia programs, and for distributing selected multimedia programs concurrently to a plurality of end-users, preferably on an on-demand, pay-per-view basis. The multimedia programs are preferably stored in a mass storage library 40 comprising one or more mass storage devices which, individually or cumulatively, include non-volatile memory devices capable of storing mass amounts of information, typically on the order of terabytes. The multimedia server 30 may include storage and distribution devices situated at a central media distribution site or may include a number of storage and distribution resources provided at a plurality of sites, with the remotely located resources communicating over a wide area network (WAN), for example.

Multimedia information is preferably stored in a compressed digital format on one or more digital storage devices 35. Suitable digital storage devices 35 include, for example, digital direct access storage devices (DASD) and digital audio tape (DAT) systems. In one embodiment, a plurality of digital DASDs may be configured as an array of DASDs operating in accordance with a known RAID (Redundant Array of Inexpensive Disks) protocol. Analog versions of multimedia programs may be stored on one or more analog storage devices 39, such as analog video tape systems and analog audio systems, for example. The mass storage library 40 may further include optical data storage systems or CD-ROM systems. It is to be understood that the mass storage library 40 may be configured with a variety of storage and processing devices covering a diverse range of technologies, and is not limited to those depicted in FIG. 4. In one embodiment, for example, the mass storage library 40 includes one or more Dynamic Random Address Memory (DRAM) storage devices 37 employed for storing multimedia information in two-dimensional or three-dimensional storage array configurations. In accordance with one embodiment, one or more DRAM storage devices 37 are employed to provide mass storage of a plurality of popular or frequently requested multimedia programs. In accordance with a novel media server formatting architecture and methodology disclosed hereinbelow, a DRAM storage device 37 advantageously provides for fast access to popular multimedia programs and high-speed asynchronous transfer mode distribution of popular multimedia programs to a plurality of end-users.

In addition to pre-recorded or pre-produced multimedia programs, the mass storage library 40 preferably communicates with a number of external communication channels for receiving real-time broadcast signals representative of programming made available over local, national, and international broadcast networks. Accordingly, a subscribing customer may request from a multiplicity of pre-produced and real-time multimedia programming selections.

In a preferred embodiment, multimedia programs stored in the mass storage library 40 are preferably initially converted from an analog format into a digital format, and then compressed or coded in accordance with an established coding algorithm. The compressed digital program segments are preferably structured in the form of a multiplexed program bitstream. A typical multiplexed bitstream comprises a video signal stream portion, an audio signal stream portion, and may further include other information signal stream portions. A multimedia program ordered by a subscribing customer is preferably transmitted to the customer location as a customized, multiplexed program bitstream representative of the selected multimedia program, preferably over an existing television channel, cable or optic television channel, digital or fiber optic telephone line, or satellite communication channel 44, for example. The discrete source program segments that comprise the subscriber-selected multimedia program bitstreams are preferably transmitted as packets of segments in an asynchronous manner over the communication channel 44 to a plurality of target set-top control system 62.

As illustrated in FIGS. 3-5, an analog video signal, typically comprising a video signal portion and an audio signal portion, is preferably converted to a digital format and compressed by a coder 32 in accordance with an established coding algorithm. The compressed digitized program bitstream is then segmented or divided into a plurality of discrete video source program segments 48 by an index parser 33. Each discrete compressed digital video segment 48 is preferably representative of a predetermined amount of non-compressed, full-motion video. In one embodiment, one second of non-compressed, full-motion video is represented by each of the compressed video segments 48. In another embodiment, two seconds of non-compressed, full-motion video is represented by each of the compressed video segments 48. It is to be understood that each of the source video segments 48 may be representative of a full-motion video portion greater than or less than one second. Alternatively, a varying duration of non-compressed, full-motion video may be represented by each of the compressed video segments 48.

Referring now to FIG. 4 in greater detail, each of the mass storage devices 35, 37, and 39 may be coupled to a corresponding index parser 33. Each of the index parsers 33, in turn, are preferably coupled to a corresponding coder 32. It is noted that the coders 32 illustrated in FIG. 4 are shown as being external to the mass storage library 40. The coders 32 may alternatively be incorporated as internal components within the mass storage library 40. In a preferred embodiment, the multimedia programs that are made available in the mass storage library 40 are processed through the coder 32 and index parser 33 only once, and then stored on a mass storage device 35. An individual multimedia program may be stored on a single mass storage device, or, alternatively, stored across a plurality of mass storage devices. When processed by the index parser 33, each of the compressed digital video segments 48 is preferably encoded with a unique segment address. A first video segment 48, for example, may be encoded or tagged with an address identifier of "A1," while the second discrete video segment 48 may be encoded with an address of "A2." As such, each of the discrete source video segments 48 is preferably locatable within the storage device by reference to its unique address. An address table may be employed to provide mapping to physical storage locations associated with a particular virtual or indirect video segment address. Having indexed each of the video segments 48 with a unique address and stored the video segments on a mass storage device, such as a digital storage device 35, reference to specific video segment 48 addresses provides an efficient means for organizing the video segments 48 in a customized manner, and transmitting the video segments 48 to a target set-top control system 62.

As further illustrated in FIG. 4, each of the mass storage devices provided in the mass storage library 40 is preferably coupled to one or more staging storage devices 41. A significant advantage of the novel multimedia server 30 concerns the capability of organizing source video segments 48 in a customized manner for reception by a particular customer's set-top control system 62. A plurality of staging devices 41 permits each storage device, such as digital storage device 35, to concurrently service a plurality of customer requests and organize requested multimedia program in a customized manner. The staging devices 41 may comprise DRAM storage devices, an array of DASDs configured to operate as a RAID system, or other digital storage systems.

As mentioned previously, one or more analog storage devices 39 may be employed to store analog multimedia information. An analog multimedia program, when requested by a subscribing customer, is preferably transferred to the coder 32, coded by the coder 32, indexed in a manner previously discussed with respect to the index parser 33, and preferably transmitted to a staging storage device 41. It is noted that each of the storage devices 35, 37, and 39 may include a corresponding video parser
38 coupled between the storage device and a staging storage device 41. It is to be understood that a single video parser 38 or single index parser 33 may be employed rather than individual parsing devices. Further, the staging devices 41 may be accessible to all of the mass storage devices, and that the distribution of work load between the components comprising the mass storage library 40 may be distributed amongst the various components to optimize the overhead of the multimedia server 30. Further, analog and digital multimedia programming received over a local, national, or international broadcast channel 45 may be respectively directed to a coder 32 or directly to an index parser 33 for processing of real-time multimedia information.

In FIG. 5, there is shown an illustration of a partial series 46 of sequentially ordered one-second compressed video segments 48 provided at the output of the coder 32. It is noted that a sequentially ordered sequence or series of video segments
48 is representative of corresponding consecutively ordered full-motion video portions of a multimedia program. Conversely, a non-sequentially ordered sequence or series of video segments 48 is representative of a corresponding non-sequential or non-consecutively ordered full-motion video portion of a multimedia program. It is to be understood that all or only a portion of the video segments 48 representative of a multimedia program may be organized as a non-sequential series of video segments
48. Further, it may be desirable to organize a predetermined number of video segments 48 as a non-sequential video segment 48 series portion of a multiplexed signal bitstream followed by or, alternatively, preceded by a sequential video segment 48
series portion. In other applications, it may be desireable to produce a multiplexed signal bitstream comprising only sequentially ordered compressed video segments 48.

In a configuration employing an MPEG-1 coder 32, for example, video compression ratios of approximately 100:1 are typically achievable. On average, one minute of full-motion video can be digitally compressed into approximately ten megabytes, corresponding to an average of approximately 5.6 kilobytes per video frame and approximately 0.167 megabytes per second of full-motion video program time at an NTSC (National Television Systems Committee) compliant display rate of thirty frames per second. It is noted that individual one-second compressed movie segments 48 typically vary in terms of size or number of bytes. On average, it has been determined that for an MPEG-1 coded video program, approximately 0.167 megabytes of memory is required to store each of the one-second compressed movie segments 48. In order to store a two-second compressed movie segment 48, for example, 0.334 megabytes of memory would generally be required.

In one embodiment, the coder 32 produces a compressed digital video bitstream of a type conforming to one or more of the MPEG coding standards. A typical video bitstream includes a sequence of discrete video information packs, with each pack including a layer header, a system header, a sequence of information carrying packets, and an end code demarcating the end of each discrete pack. The pack layer header generally contains a pack start code, or sync code, used for synchronization purposes, and a system clock value. The system header generally contains a variety of information, such as system stream identification information, which is used to differentiate the video pack data from other data incorporated into the multiplexed signal stream. Each of the information carrying packets defined within a pack typically contains either encoded audio or encoded video signal stream data. It is noted that the information carrying packets typically include a video packet header, while packets containing audio information typically include an audio packet header. Generally, video signal data corresponding to a plurality of video frames is contained within each video packet, while corresponding audio signal data is contained within an associated audio packet.

In one embodiment, the coder 32 digitally compresses the video and audio information corresponding to a predefined duration of full-motion video, such as one-second of motion video, into each video and corresponding audio pack. By way of example, a one-second portion of full-motion video conforming to an NTSC video format contains thirty frames of motion video. In this example, it will be assumed that each pack contains six video packets. Accordingly, one second of motion video may be represented by five packs, each of which contains six video packets. It is to be understood that the MPEG coding standard, as well as other coding standards, provide for an appreciable amount of flexibility when packetizing multimedia information in a compressed digital format.

Accordingly, the coder 32 preferably cooperates with the index parser 33 to produce a multiplexed signal bitstream at the output of the index parser 33 which includes a plurality of compressed video segments 48, with each segment 48 representing a predefined duration of full-motion video. Additionally, the coder 32 and index parser 33 cooperate to generate a unique index address for each of the discrete video segments 48. The unique address information may be incorporated into the pack layer header or system header portion of each pack or segment. As previously mentioned, the indexed sequential series of compressed video segments 48 is then preferably stored on a suitable mass storage device, such as the digital storage device 35 or DRAM storage device 37 illustrated in FIG. 4. Since each of the discrete video segments 48 contains a unique index address, the video parser 38 effectuates efficient reorganization of a sequential series of stored, compressed video segments 48 into a custom ordered series of video segments 48 by referencing the unique address of specific video segments 48.

A sequential series 46 of compressed digital video segments 48 provided at the output of the coder 32 is preferably transmitted to the input of an index parser 33, as shown in FIG. 4. A controller 34, coupled to the coder 32 and video parser 38, preferably coordinates the transfer of the compressed video segments 48 from the coder 32 and index parser 33 to a mass storage device 35 provided in the mass storage library 40. The video parser 38 is preferably employed to perform various re-ordering operations on a sequential series 46 of compressed video segments 48 associated with a selected multimedia program stored on the mass storage device 35. The video parser 38 operates to positionally translate particular discrete video segments 48 of a sequential video segment series 46 to produce a custom ordered series 54 of video segments 48. The custom ordered video segment series 54 shown in FIG. 6, for example, depicts the first thirty compressed video segments 48 of a customized video signal stream 54, representative of the first thirty seconds of a two-hour movie, produced at the output of the video parser 38 for temporary storage on a staging storage device 41. As will be described in greater detail hereinbelow, the manner in which the video parser 38 parses the video segments 48 to produce a customized video signal stream 54 is preferably dependent on a number of factors, including the storage capacity and functionality of a subscriber's local set-top control system 62 adapted to receive and process the customized video signal stream 54, and the manner in which a subscribing customer desires to control the presentation of a requested multimedia program.

The controller 34 preferably controls the transfer of a customized video segment series 54 from the video parser 38 to a staging storage device 41 for temporary storage thereon prior to transmission to a distribution switch 42. The distribution switch 42, which is coupled to a communication channel 44, is preferably an ATM (Asynchronous Transfer Mode) distribution switch which operates to asynchronously distribute packets, or packs in accordance with MPEG terminology, of video segments 48
concurrently to one or more customer set-top control systems 62 over the communication channel 44. It is to be understood that one or more buffer memory devices (not shown) may be employed when synchronizing the transmission of video segments 48
comprising a multiplexed signal stream between the video parser 38 and the distribution switch 42, and for synchronizing segment packet transmission between the distribution switch 42 and the communication channel 44.

It is to be further understood that a customized video segment sequence 54 representative of a multimedia program may alternatively be stored on the mass storage device 35 to facilitate efficient transmission of one or more pre-processed, standard customized video signal streams 54 to customer set-top control systems 62 having a predefined storage capacity and control function capability. Use of such pre-processed customized video signal streams retrieved from the mass storage device 35
obviates repetitive parsing operations that would otherwise be performed by the video parser 38 to accommodate a particular set-top control system's unique configuration and presentation control functionality. Generally, the process of encoding a multimedia program requires significantly greater processing resources and a correspondingly greater processing cost as compared to decoding operations. Pre-processing or encoding multimedia programs in a manner amenable to such standardized set-top control system 62 disproportionately shifts the processing overhead to the multimedia server 30, as well as the concomitant processing costs which can be shared by the subscribing customers. It is noted that prior to transmitting a video program to a subscribing customer's set-top control system 62, the subscriber's account status is preferably verified by a billing system 36 coupled to the controller 34 of the multimedia server 30. After proper account verification is confirmed, the subscribing customer is granted authorization rights to receive multimedia programming from the multimedia server 30 preferably on a pay-per-view basis.

In FIGS. 7 and 8, there are illustrated matrices of discrete compressed video segments 48 shown in row-column array formats. In one embodiment, an entire video program, such as a feature-length movie or theatrical performance, for example, is processed by the coder 32 and index parser 33 into a sequential series 46 of compressed video segments 48 which is subsequently organized by the video parser 38 into a matrix of rows and columns, as illustrated in FIGS. 7 and 8. It is noted that various known matrix manipulation techniques may be employed by the video parser 38 when re-organizing the ordering of the video segments 48 representative of all or a portion of a multimedia program. Techniques other than those that employ matrix manipulation may also be utilized. In accordance with the embodiments illustrated in FIGS. 7 and 8, the video parser 38 initially organizes a sequential series of discrete compressed video segments 48 into a matrix having 60 rows and N columns, where N is the number of minutes of total playing time for a particular video program, rounded upward.

For purposes of clarity and simplicity of explanation, the matrix illustrated in FIG. 7 is shown as containing all of the discrete compressed video segments 48 of a two-hour segmented movie, with each video segment 48 representing a one-second portion of non-compressed, full-motion video. A two-hour movie segmented into such one-second, full-motion video portions is thus represented by 7,200 discrete compressed video segments 48. The 7,200 compressed movie segments 48 are preferably organized by the video parser 38 as a matrix of 60 rows and 120 columns. It is noted that the value of N for a two-hour movie is equal to 120 minutes, thereby accounting for the 120 columns of the matrix depicted in FIG. 7. In one embodiment in which a multimedia program is to be transmitted exclusively as a sequential series of video segments 48 without a non-sequential series portion, as further illustrated by the matrix configuration illustrated in FIG. 7, the video parser 38 preferably transmits the compressed video segments 48 sequentially arranged in the 60.times.120 matrix to the distribution switch 42 in a column-by-column manner. The video segments A1 through A7200 representing a two-hour movie 48 may then be transmitted in a sequential manner over the communication channel 44 to a subscribing customer's set-top control system 62. A subscribing customer's set-top control system 62 preferably includes a moderate amount of local storage, typically on the order of 5 to 10 megabytes, for receiving the compressed sequential video signal stream 46 transmitted from the multimedia server 30. Dynamic Random Access Memory (DRAM) or a DASD may be employed to buffer the 5 to 10 megabytes of the received compressed sequential video signal stream
46.

In accordance with this embodiment the multimedia server 30 preferably communicates concurrently with a plurality of set-top control systems 62 over a communication channel 44. A typical coaxial cable communication channel 44 transmits information signals at a data rate on the order of approximately 100 megabytes per second. Assuming that each of a plurality of set-top control system 62 includes approximately ten megabytes of internal memory, for example, the distribution switch 42 of the multimedia server 30 preferably asynchronously transmits approximately ten megabytes of multimedia program information each minute to some 600 subscribing customer locations. It is noted that a set-top control system 62 configured with a minimal amount of local memory is capable of receiving and processing the sequentially ordered compressed video signal stream 46 transmitted by the multimedia server 30, but will typically lack sufficient local memory to provide a subscriber with VCR-type control over the presentation of the video program.

In accordance with two other embodiments, as illustrated in FIGS. 8 and 9, the video parser 38 preferably arranges a sequential stream 46 of compressed video segments 48 received from a mass storage device 35 into a customized sequence of compressed video segments 48. In FIG. 8, there is illustrated a customized matrix of 7,200 compressed video segments 48 representing 7,200 discrete one-second full-motion video portions of a two-hour video program. In the embodiment illustrated in FIG.
8, the video parser 38 organizes the 7,200 compressed video segments 48 into two sub-matrices 50 30 and 52 of odd and even address indices. Each of the two sub-matrices 50 and 52 is preferably arranged as a sub-matrix comprising ten rows and 360 columns (10.times.360). Each of the sub-matrices 50 and 52 thus contains 3,600 discrete video segments 48 of the total 7,200 segments 48 comprising the two-hour video program. The odd sub-matrix 50 and the even sub-matrix 52 are then concatenated along the first dimension (rows) to form a single customized matrix 51 of twenty rows by 360 columns (20.times.360). In response to a transmission control signal produced by the controller 34, the video parser 38 preferably transmits the compressed video segments
48 arranged in the customized matrix 51 to a staging storage device 41 which, in turn, transmits the customized non-sequential video segments 48 to the distribution switch 42 in a column-by-column manner for subsequent transmission over the communication channel 44.

For example, the video parser 38 preferably transmits the video segments 48 of the customized matrix 51, shown in FIG. 8, to the distribution switch 42 as the customized sequence of A1, A3, A5, A7, A9 . . . A19; A2, A4, A6, A8 . . . A20; A21, A23, A25 . . . A39; A22, A24, A26, A28 . . . A40; A41, A43 . . . A7200. Each of the sub-matrices 50 and 52 defining the customized concatenated matrix 51 will hereinafter be respectively referred to as block 50 and block 52. Preferably, each block
50 and 52 will exclusively contain video segments 48 having either even or odd address indices. It is noted that this preferred block organization is not necessarily required in order to realize the advantages of the novel multimedia server 30. In the embodiment illustrated in FIG. 8, the video segments 48 processed by the video parser 38 are subdivided into one odd block, Block-A 50, and one even block, Block-B 52, for a total of two such blocks. The total number of blocks within which the video segments 48 are organized will be referred to herein in connection with the Block Indexing Coefficient (BI) associated with the customized video segment matrix 51. The customized matrix 51 of FIG. 8 includes two blocks of odd and even indices, and as such, represents a customized matrix 51 having a Block Indexing Coefficient of modulo-2. It is to be understood that the compressed video segments 48 may be organized into a plurality of odd and even blocks to define customized matrices 51 having Block Indexing Coefficients in excess of modulo-2. Also, each block of a plurality of blocks may include a combination of odd and even video segment address indices.

As will be discussed in detail hereinbelow, the length of each segment block (L), measured in terms of video segments 48, is an important formatting parameter. The segment block length (2) is a function of the size of an input buffer typically provided in a subscribing customer's set-top control system 62 for the purpose of buffering packets of video segments 48 received from the multimedia server 30. The organization of each of the blocks 50 and 52 formatted as shown in FIG. 8, for example, would generally correspond to a maximum block length of ten video segments 48, and a maximum packet size of ten video segments 48. As such, the input buffer of a customer's set-top control system 62 would typically be configured to store at least ten video segments 48. By way of further example, the organization of each of the blocks 53, 55, 57, and 59 formatted as shown in FIG. 9 would correspond generally to a maximum block length of five video segments 48, and a maximum packet size of five video segments 48. As such, the input buffer of a customer's set-top control system 62 would typically be configured to store at least five video segments 48. It is noted that the average size of the discrete video segments 48 must be considered when determining the adequacy of the input buffer 66 storage capacity. Each of the video segments 48 shown in FIG. 8, for example, represents a one-second portion of full-motion video, while each of the video segments 48 shown in FIG. 9, for purposes of illustration, represents a two-second portion of full-motion video.

Generally, the input buffer 66 should be configured to store at least twice the number of video segments contained in the largest video segment packet transmitted by the multimedia server 30. The additional input buffer 66 storage capacity provides for enhanced synchronization of video segments 48 being processed through the input buffer 66, and provides the multimedia server 30 with additional flexibility when asynchronously distributing video segment packets to a plurality of customer set-top control systems 62. It may be advantageously efficient, for example, for the multimedia server 30 to transmit two packets during a single transmission window to a particular set-top control system 62 to reduce server 30 processing overhead during periods of peak utilization.

Referring now to FIG. 9, there is illustrated a customized matrix 51 having a Block Indexing Coefficient of modulo-4 and comprising four blocks 53, 55, 57, and 59 of compressed two-second video segments 48 having alternating odd and even address indices. In the embodiment of FIG. 9, the two-hour video program segmented by the coder 32 and the index parser 33 has been organized by the video parser 38 into four blocks, Block-A 53, Block-B 55, Block-C 57, and Block-D 59. In response to a transmission control signal produced by the controller 34, the compressed video segments 48 arranged in the four blocks 53, 55, 57, and 59 are read out of the video parser 38 in a column-by-column manner and transferred to a staging storage device 41 for subsequent transmission over the communication channel 44 by the distribution switch 42. In accordance with one formatting scheme, the video parser 38 preferably transmits the video segments 48 of the customized matrix 51 to the staging storage device
41 as the customized sequence of A1, A5, A9, A13, A17; A2, A6, A10, A14, A18; A3, A7, A11, A15, A19; A4, A8, A12, A16, A20; . . . A3600. It can be seen that the ordering of the video segments 48 comprising a customized video signal stream 54 becomes more asynchronous or non-sequential as the Block Indexing Coefficient of the customized matrix 51 increases. As will be described in detail hereinbelow, the organization of the video segments 48 comprising a customized video signal stream 54 is preferably governed by general asynchronous formatting equations and guidelines that have been developed by the inventors. These formatting equations and guidelines are preferably employed by the multimedia server 30 to optimally organize a segmented multimedia program in response to various performance and functional characteristics of each unique set-top control system 62 adapted to receive the multimedia program transmission from the multimedia server 30.

In general, a customized video signal stream 54 preferably includes an initial asynchronous or non-sequential video segment 48 portion followed by a synchronous or sequential video segment 48 portion. More particularly, an introductory portion of a selected multimedia program signal stream preferably includes a plurality of non-sequentially ordered video segments 48, while the remaining portion preferably includes a plurality of sequentially ordered video segments 48. In a preferred embodiment, the duration of the introductory non-sequential portion of the multimedia program signal stream corresponds to the duration of the multimedia program that is to be buffered on the subscriber's set-top control system 62, and is preferably the portion of the multimedia program over which a customer has full local VCR-type presentation control. Further, as will be discussed in detail hereinbelow, the asynchronous portion of the multimedia program is concurrently buffered on the customer's set-top control system 62 while being processed for immediate display on an attached television 24 or monitor, thereby providing a subscribing customer with true on-demand viewing of a selected multimedia program. It is to be understood that a customized video signal stream may comprise only asynchronously ordered video segments 48, combined synchronous and asynchronous video segment 48 portions, or exclusively synchronously ordered video segments 48.

In accordance with the embodiments illustrated in FIGS. 8 and 9, a set-top control system 62 adapted to receive a customized video signal stream 54 transmission from the multimedia server 30 must generally include sufficient memory to buffer all or at least a portion of the video signal stream 54 and include means for reorganizing the asynchronous video stream portion into a sequentially ordered video signal stream 46 in order to properly display the multimedia program in accordance with its original temporal organization. It is important to note that cooperative operation between the multimedia server 30 and a set-top control system 62 provides for a media-on-demand communication system capable of concurrently servicing a plurality of subscribing customers, with each customer having full local VCR-type control over the presentation of a portion of the multimedia program or, if desired, the entire multimedia program. It is further noted that the novel parsing or formatting of a segmented multimedia program by the video parser 38 and concurrent asynchronous transmission of one or more multimedia programs by the distribution switch 42 provides for a dramatic reduction in communication channel 44 bandwidth and multimedia server 30
processing overhead in comparison to conventional video communication systems. By transmitting each of the compressed video segments 48 generally only once, repetitive transmission of video segments 48 over the communication channel 44 that would otherwise be required to provide local VCR-type control over the media presentation is altogether avoided.

The distribution switch 42 preferably transmits a plurality of selected multimedia programs concurrently to a plurality of set-top control systems 62. In order to effectuate high-speed, high-volume multimedia program transmission, the distribution switch 42 preferably employs an Asynchronous Transfer Mode (ATM) switching methodology. Generally, ATM is a cell-based switching and multiplexing methodology designed to be a general-purpose, connection-oriented transfer mode for a wide range of communication services. ATM is widely utilized for effectuating communication over local area networks (LANs) and private networks.

ATM handles both connection-oriented traffic and connectionless traffic through the use of adaptation layers. ATM virtual connections may operate at either a constant bit rate (CBR) or a variable bit rate (VBR). Each ATM cell transmitted over a communication channel 44 contains addressing information that establishes a virtual connection from origination to destination. All cells are then transferred, in order, over this virtual connection. ATM provides bandwidth-on-demand, and also supports LAN-like access to available bandwidth. ATM is asynchronous because the transmitted cells need not be periodic as time slots of data are in accordance with known Synchronous Transfer Mode (STM) methodologies.

The primary ATM information unit is the cell. ATM standards define a fixed-size cell with a length of 53 octets (or bytes) comprised of a 5-octet header portion and a 48-octet payload portion. The bits in the cells are transmitted over the transmission path 44 in a continuous stream. Cells are mapped into a physical transmission path, such as the North American Digital Signal Level 1 (DS1), DS3, or SONET, International Telecommunications Union--Telecommunications standardization sector (ITU-T) STM standards, and various other local fiber and electrical transmission systems.

All information is switched and multiplexed in an ATM distribution network typically by using these fixed-length cells. The cell header identifies the destination, such as a subscriber's set-top control system 62, cell type, and priority. Fields of the cell header include the virtual path identifier (VPI) and virtual circuit identifier (VCI) which identify the destination. The generic flow control (GFC) field allows a multiplexer, such as the distribution switch 42, to control the rate of cell transmission. The payload type (PT) indicates whether the cell contains user data, signaling data, or maintenance information. The cell loss priority (CLP) bit indicates the relative priority of the cell. It is noted that higher priority cells are granted preferred processing status over lower priority cells during congested intervals.

Each cell typically includes a header error check (HEC) which detects and corrects errors in the header. The payload field is passed through the network intact, generally without undergoing error checking or correction. ATM relies on higher layer protocols to perform error checking and correction on the payload portion. The fixed cell size simplifies the implementation of ATM switches and multiplexers while providing very high speeds. When using ATM, longer packets cannot delay shorter packets as in other switching implementations because long packets are segmented into many cells. This enables ATM to carry constant bit rate (CBR) traffic together with variable bit rate (VBR) data traffic.

As will be appreciated by those skilled in the art, an ATM communication network suitable for communicating a plurality of multimedia programs from a multimedia server 30 concurrently to a plurality of set-top control systems 62 preferably conforms to the Open Systems Interconnection (OSI) model. The OSI model defines seven layers, including an application, presentation, session, transport, network, link, and physical layer, for describing the operations of an OSI communication network. The OSI model was developed by the International Organization for Standardization (ISO) and is described in "The Basics Book of OSI and Network Management" by Motorola Codex from Addison-Wesley Publishing Company, Inc., 1993 (First Printing September
1992). In one embodiment, the distribution architecture and method for distributing multimedia information from the multimedia server 30 to a plurality of distantly located set-top control systems 62 preferably conforms to one or more of the OSI communication models.

In accordance with one embodiment, the distribution switch 42, illustrated in FIGS. 3 and 4, preferably transmits each packet of discrete video segments 48 to a target set-top control system 62 within a predetermined transmission window, the duration of which is preferably determined by the configuration and functional attributes of a particular customer's set-top control system 62. The customized non-sequential series of video segments 48 illustrated in FIG. 6, for example, represents a video segment series portion exhibiting a relatively modest degree of asynchronous organization. For this example, each video segment packet transmitted by the distribution switch 42 over the communication channel 44 preferably contains two video segments 48, one of which has an odd address index, such as A1, and the other of which has an even address index, such as A2. Accordingly, an input buffer provided in a customer's set-top control system 62 would be configured to store at least two video segments 48. Assuming that each of the two video segments 48 buffered in the input buffer contain a one-second portion of motion video, the input buffer would be emptied after two seconds, which corresponds to the time required to display the two one-second video segments 48.

In order to provide uninterrupted presentation of the multimedia program, the next packet containing another two one-second video segments 48 would have to be transmitted by the distribution switch 42 and received by the set-top control system 62
within a two second transmission window. Accordingly, after the second video segment 48 of a particular video packet is being read out of the input buffer, the first and second video segments of the subsequently received video packet is preferably read into the input buffer. It is noted that the input buffer is preferably configured to store in excess of the minimum required capacity to provide for increased multimedia server 30 transmission flexibility and enhanced input buffer processing synchronization. In this example, an input buffer configured to store three or four video segments 48, rather than the required minimum of two video segments 48, is preferred. Alternatively, an overflow buffer or transfer buffer could also be employed in cooperation with the input buffer to facilitate efficient synchronization.

By way of further example, a customized non-sequential series of video segments 48 read out of the customized matrix 51 illustrated in FIG. 9 represents a video segment series portion exhibiting a relatively moderate degree of asynchronous organization. For this example, as further illustrated in FIG. 10, each video segment packet transmitted by the distribution switch 42 over the communication channel 44 preferably contains at least five video segments 48. After the first four packets have been transmitted, each of the packets for this example would contain only four video segments 48. As such, the input buffer provided in a customer's set-top control system 62 would be configured to store at least five video segments 48. Assuming that each of the five video segments 48 buffered in the input buffer represents a two-second portion of motion video, the input buffer would be emptied after ten seconds of equivalent viewing time for the first four packet transmissions, and would be emptied after eight seconds of equivalent viewing time for subsequently transmitted video segment packets.

In order to provide uninterrupted presentation of the multimedia program for this example, Packets 2 through 5 would have to be transmitted by the distribution switch 42 and received by the set-top control system 62 within a ten second transmission window. The transmission of the packets following Packet 5 would have to be transmitted by the distribution switch 42 and received by the set-top control system 62 within an eight second transmission window. It is considered desirable for purposes of simplicity that the number of video segments 48 contained within each packet be an integral multiple of a one-second video segment 48. It is noted that information packets unrelated to the instant multimedia program selection may also be transmitted to a customer's set-top control system 62 from the multimedia server 30. The packets containing the unrelated information, such as a message indicating that a video conferencing call has been received or reception of some other unrelated data, may be interleaved with the video segment packets and transmitted within an appropriate transmission window. Further, the unrelated information may be interleaved between discrete video segments 48 contained within a video segment packet.

Conventional coaxial transmissions cables are generally capable of supporting burst transmission rates on the order of 100 MB/sec. Fiber optic transmission lines, in contrast, can be employed to support burst transmission rates on the order of gigabytes per second. Accordingly, transmission window durations on the order of several seconds can easily be accommodated using existing coaxial and fiber optic communication networks. It is readily apparent to those skilled in the art that various known asynchronous transmission mode distribution techniques are well-suited for distributing video segment packets asynchronously during successive transmission windows or transmission time slots over a relatively high burst rate communication channel.

The service costs associated with receiving on-demand multimedia programs on a pay-per-view basis preferably vary depending on the formatting of the source program signal stream transmitted from the multimedia server 30. In general, a subscribing customer's service costs decrease as the video segment packet size transmitted by the multimedia server 30 increases. Video segment packets containing two one-segment video segments 48, for example, must be transmitted within a relatively short transmission window of approximately two seconds. The multimedia server 30 must, therefore, transmit video packets on a frequent basis. In contrast, a source multimedia program formatted such that four or five video segments 48 are contained within each video segment packet, for example requires significantly fewer packet transmissions, with each transmission being accomplished within a significantly longer transmission window of approximately ten and eight seconds, respectively. Although increasing the size of the input buffer generally increases the cost of the set-top control system 62, the amortized cost of receiving on-demand multimedia programming over time is reduced due to the ability to buffer larger video segment packets.

Intelligent Set-Top Control System

Referring now to FIG. 11, there is illustrated a system block diagram of a novel intelligent set-top control system 62 adapted for communicating with a remote multimedia server 30 preferably of the type described hereinabove. In accordance with one embodiment, a relatively low-cost set-top control system 62 configuration includes a moderate amount of local memory, preferably on the order of 5 to 10 megabytes, for receiving a coded video signal stream 46 comprised of sequentially ordered discrete video segments 48 transmitted from the multimedia server 30 over a communication channel 44. The set-top control system 62 preferably includes a set-top controller 64 that communicates with an input buffer 66, output buffer 72, and a decoder 74
to coordinate decoding of the received coded video signal stream 46 for presentation on a local monitor or television 76. As previously discussed, the relatively small storage capacity of the input buffer 66 of the low-cost set-top control system 62
will generally require relatively frequent packet transmissions for the multimedia server 30, thereby resulting in higher service costs in comparison to set-top control systems employing large storage capacity input buffers 66.

In a preferred embodiment, the set-top control system 62 preferably includes a novel multimedia direct access storage device (DASD) 68 adapted to buffer compressed video segments 48 representative of a portion or all of a multimedia program received from a communication channel 44 in accordance with a novel formatting methodology disclosed hereinbelow. An important feature afforded a subscribing customer when employing a set-top control system 62 in accordance with this embodiment concerns the capability to effectuate full local VCR-type control over the presentation of a portion of a selected multimedia program on a real-time basis. Full VCR-type control over the presentation of the entire multimedia program may also be realizable provided a sufficient amount of DASD 68 storage capacity is allocated for this purpose.

The amount of available DASD 68 storage capacity generally impacts the degree to which a subscribing customer can effectuate VCR-type control over the presentation of a selected multimedia program. As illustrated in FIG. 12, a subscriber preferably controls the presentation of a portion of a multimedia program defined within a virtual presentation control window 90. The functionality of the virtual presentation control window 90 is facilitated by a novel asynchronous formatting methodology and storage architecture associated with the multimedia DASD 68. The presentation control window 90 depicted in the embodiment illustrated in FIG. 12, for example, is shown as encompassing a thirty minute portion of a two-hour (120 minute) movie. The portion of the movie represented within the presentation control window 90 is locally manipulatable by the subscriber. The subscriber, for example, may progress through the movie portion defined within the presentation control window 90 in a forward and a reverse temporal direction, and may also pause the presentation of the movie.

The presentation control window 90 preferably advances in time as the movie is being presented. In this regard, the virtual presentation control window 90 may be viewed as a temporally translatable buffer. The presentation control window 90
preferably comprises a forward window portion 93 and a reverse window portion 91 defined respectively on either side of a current viewing time reference 95. At a current viewing time of sixty minutes into a two-hour movie, for example, the forward window portion 93 of the thirty minute presentation control window 90 provides control over the succeeding fifteen minutes (minutes sixty through seventy-five) of the movie with respect to the current viewing time reference 95, while the reverse window portion 91 provides control over the preceding fifteen minutes (minutes forty-five through sixty) with respect to the current viewing time reference 95.

The thirty minute presentation control window 90 is translated in either a forward or reverse temporal direction in accordance with the forward and reverse progression of the current viewing time reference 95. As such, for current viewing time references 95 within the two-hour movie in excess of fifteen minutes and less than 105 minutes, a viewer may progress forward or backward through a maximum of fifteen minutes in either temporal direction with respect to the current time reference 95. The time increments associated with progressing in a forward or reverse temporal direction within the presentation control window 90 are typically determined by a number of factors, including the storage capacity of the DASD 68 and the number of disk surfaces and disk surface portions or blocks allocated for supporting the presentation control window 90, the size of the input buffer 66 of the set-top control system 62, the size of each discrete video segment 48, and the size of each video segment packet. As long as the viewer operates within the thirty minute presentation control window 90, each of the 7,200 compressed video segments 48 comprising the two-hour movie is transmitted only once from the multimedia server 30 to the subscriber's set-top control system 62. Moving outside of the presentation control window will generally require re-transmission of previously transmitted compressed video segments 48. Such incidents of re-transmission preferably result in additional costs being charged to the subscriber's account.

With further reference to FIG. 11, the set-top controller 64 of the set-top control system 62 preferably communicates with a remote multimedia server 30 over a communication channel 44, and coordinates the operation of the set-top control system
62. Media-on-demand data is generally transmitted from the multimedia server 30 to the set-top control system 62 over the communication channel 44 at a very high burst data rate, typically on the order of 100 megabytes per second (MB/sec) for a conventional coaxial transmission cable. The set-top controller 64 preferably communicates with other components of the set-top control system 62 to coordinate the reception, storage, and decoding of compressed video segments 48 received from the multimedia server 30, and the presentation of the decoded video segments 48 on a subscribing customer's television 76. The set-top controller 64 preferably communicates control signals to the multimedia server 30 over a server control line or channel 78
of the communication channel 44 to initiate transmission of a pay-per-view multimedia program and to regulate the rate at which the compressed video signal stream is received from the multimedia server 30 over the data channel 75 to avoid an input buffer
66 overflow condition.

During the presentation of a multimedia program, for example, the viewer may temporarily stop the presentation of a program by communicating a pause command to the set-top control system 62, typically by use of an IR remote control handset 25. During the pause mode, a control signal is preferably issued by the set-top controller 64 to the multimedia server 30 over the server control line 78 to request temporary halting of source video signal stream transmission, thus causing the translatable presentation control window 90 to temporarily remain stationary. The set-top controller 64 preferably issues a resume control command over the server control line 78 when requesting the multimedia server 30 to resume transmission of the source video signal stream. By way of further example, a subscribing customer may view portions of the multimedia program outside of the presentation control window 90 by selectively activating a forward or reverse control button disposed on the IR remote control handset 25. In accordance with a novel multimedia DASD 68 video signal stream buffering methodology, only the compressed video segments 48 corresponding to portions of the multimedia program defined within the presentation control window 90 are locally stored in the DASD 68. Thus, moving beyond the presentation control window portions 93 and 91 generally requires re-transmission of video segments 48 corresponding to portions of the movie outside of the presentation control window 90.

The set-top control system 62 preferably includes an annunciator that alerts a subscriber to a condition in which a forward or reverse control request issued from the IR remote control handset 25 can not be satisfied within the currently defined presentation control window 90. The annunciator also preferably alerts the subscriber that satisfying the request will require additional video data from the multimedia server 30 and result in an associated charge to the subscriber's account. A subscriber may initiate transmission of the additional video data preferably by activating a combination of control buttons in order to ensure that the subscriber intends to incur the additional expense.

As the set-top controller 64 receives compressed video segments 48 from the communication channel 44, typically in the form of segment packets, the controller 64 coordinates the transfer of the segments 48 to an input buffer 66. The set-top controller 64 communicates control signals to the input buffer 66, DASD 68, output buffer 72, decoder 74, and multimedia server 30 to regulate timing and data transmission within the set-top control system 62 respectively over control lines 80, 82, 86,
88, and 78. The operation of the transfer buffer 70 is also controlled by the set-top controller 64 over control line 84. The transfer buffer 70 may be used for an number of purposes, including receiving video segments 48 from the input buffer 66 in response to an input buffer overflow condition, temporarily buffering video segments being transferred into and out of the DASD 68 to enhance synchronization, and to buffer information packets and other data unrelated to the video segment 48 data prior to being stored on or read from the DASD 68. Transferring of such non-related data to and from the DASD 68 is preferably accomplished during periods of low DASD 68 utilization, such as during a pause mode or other period of low DASD 68 usage.

In one embodiment associated with a relatively low-cost set-top control system 62, the size of the input buffer 66 is preferably sufficient to accommodate at least two one-second compressed video segments 48. As previously discussed, one second of full-motion video corresponds on average to an MPEG-1 compressed video segment 48 of approximately 0.167 MB in size. Accordingly, 0.333 MB of input buffer 66 storage capacity is required to accommodate two one-second compressed video segments 48. Data from the input buffer 66 is then transmitted to the DASD 68 preferably at a burst data rate of approximately 5 MB/sec and stored therein in a novel manner that provides full local VCR-type control of the multimedia program presentation. The size of the input buffer may be configured to store in excess of two video segments 48, and may comprise several megabytes of memory. An input buffer 66 configured to store fifteen one-second MPEG-1 compressed video segments 48 would, for example, require approximately 2.5 MB of memory.

Immediate viewing of a requested multimedia program is facilitated by the concurrent transferring of video data from the input buffer 66 to both the DASD 68 and the output buffer 72. Compressed video segments 48 transmitted from the DASD 68 or the transfer buffer 70 are received in sequential order by the output buffer 72. The output buffer 72 preferably stores a predetermined number of compressed video data and ensures that a prescribed input video data rate to the decoder 74 is maintained. Each of the sequential compressed video segments 48 received by the output buffer 72 is then decoded by the decoder 74, and transmitted to a subscriber's television or video monitor 76 at the required frame rate, typically 30 frames per second for an NTSC formatted video signal, or 25 frames per second for a PAL (Phase Altering Line) formatted video signal. In a preferred embodiment, the decoder 74 is configured to decode a compressed MPEG video bitstream. The output buffer 72, for example, preferably transfers an MPEG-1 video bitstream to the input of an MPEG-1 decoder 74 at a rate of approximately 0.2 MB/sec, thus ensuring that the decoder 74 transmits a corresponding decoded video signal to the subscriber's television 76 at a data rate of approximately 20 MB/sec. The output buffer 72 is preferably configured to buffer at least two compressed video segments 48. As such, two one-second compressed video segments 48 would require approximately 0.334 MB of output buffer 72 storage, for example, while two three-second compressed video segments 48 would require approximately 1.0 MB of output buffer 72 memory.

In one embodiment, each set-top control system 62 is identified by a unique serial number. This serial number is preferably used as an identification address when routing video data from the multimedia server 30 to the set-top control system 68
of the subscribing customer who placed the pay-per-view order. As discussed previously hereinabove, an ATM information cell typically includes a cell header that identifies the destination of the cell and its associated information payload. The unique serial number or other type of unique identifier may be incorporated into the cell header to facilitate proper routing of cells, which can be viewed as equivalent to or incorporating the discrete packets of video segments 48 transmitted to a particular subscriber's set-top control system 62.

Multimedia Direct Access Storage Device (DASD)

Turning now to FIGS. 13 and 14, there is illustrated a novel multimedia DASD 68 adapted for use in a set-top control system 62 preferably of the type previously disclosed. The multimedia DASD 68 preferably includes one or more rigid data storage disks 108 which are stacked coaxially in a tandem spaced relationship and rotated about a hub of a spindle motor 114. An actuator 118 typically includes one or more outwardly extending actuator arms 112, with each arm having one or more transducer/slider assemblies 116 mounted thereto for writing and reading information to and from the data storage disks 108. The transducer/slider assembly 116 is typically designed as an aerodynamic lifting body that lifts the transducer off of the surface of the disk 108 as the rate of spindle motor 114 and disk 108 rotation increases, thus causing the transducer/slider assembly 116 to hover above the disk 108 on an air bearing produced by the disk 108 rotation. For a DASD 68 configuration employing a constant contact transducer/slider assembly 116 arrangement, a conformal lubricant is preferably disposed on the disk surface 108 to reduce static and dynamic friction between the transducer/slider assembly 116 and the disk surface 24.

The actuator 118 is usually mounted to a stationary actuator shaft 122, and rotates on the shaft 122 to move the actuator arms 112 into and out of the stack of data storage disks 108. A coil assembly 123, mounted to the actuator 118, generally interacts with a permanent magnet structure 120, causing the actuator arms 112, in turn, to sweep over the surface of the data storage disks 108. The spindle motor 114 typically includes a poly-phase a.c. motor or, alternatively, a brushless d.c. motor adapted for rotating the data storage disks 108.

The coil assembly 123 and the permanent magnet structure 120 operate in cooperation as an actuator voice coil motor responsive to control signals produced by a DASD controller 67 typically mounted on a circuit card 124. Various other electronic modules for controlling the operation of the multimedia DASD 68 and for communicating with other devices, such as a DASD array controller or communication channel 44 interface, for example, are also typically mounted to the circuit card 124. The actuator voice coil motor produces a torquing force on the actuator coil assembly 123 when control currents of varying direction and magnitude flow in the coil assembly 123 in the presence of a magnetic field produced by the permanent magnet structure
120. The torquing forces imparted on the actuator coil assembly 123, in turn, cause corresponding rotational movement of the actuator arms 112 in directions dependent on the polarity of the control currents flowing in the coil assembly 123. The DASD controller 67 preferably includes control circuity to coordinate the transfer of data to and from the data storage disks 108, and cooperates with the actuator voice coil motor to move the actuator arms 112 and transducer/slider assemblies 116 to prescribed locations on the disk 108 when writing and reading data to and from the disks 108.

Referring now to the embodiment illustrated in FIGS. 15 and 16, video data transferred from the set-top controller 64 to the multimedia DASD 68 is preferably stored on both the upper surface 102, shown in FIG. 15, and lower surface 104, shown in FIG. 16, of the data storage disks 108. Upper and lower transducer/slider assemblies 116 and 117 are preferably provided for respectively writing and reading data to and from each of the upper and lower disk surfaces 102 and 104. It is noted that the number of data storage disks 108 may vary, and that it is not generally essential to utilize both disk surfaces 102 and 104 for purposes of storing the video data. Further, only a portion of a disk's data band may be allocated for purposes of storing video segment information, while reserving other portions of the data band for storing other types of information. Also, several non-contiguous portions of the data band may be utilized for storing video data.

With further reference to FIGS. 15 and 16, there is shown in greater detail a preferred orientation of the data tracks disposed on the upper and lower disk surfaces 102 and 104, respectively. FIG. 15 depicts the upper surface 102 of the disk 108
as viewed from above, while FIG. 16 depicts the lower surface 104 of the disk 108 as viewed from below. For clarity of orientation with respect to FIGS. 15 and 16, the direction of disk rotation is indicated by the arrows, and the actuator arms 112 are shown outlined against the respective disk surfaces 102 and 104. In a preferred embodiment, the data tracks of the upper and lower disk surfaces 102 and 104 respectively include spiral data tracks 111 and 110 for storing video information and other data. As discussed previously, the advantages of the novel media-on-demand communication system described herein are addressed with general reference to a video program for purposes of explanation, and not of limitation. Accordingly, the preferred spiral data track configuration illustrated in FIGS. 15 and 16 may be employed to store audio, textual, graphical, image, animation, and combinations of these and other types of multimedia information.

The spiral data track 110 disposed on the lower surface 104 of the disk 108 preferably contains a sequence of data storing blocks originating near the outer edge 105 of the disk 108 and spiraling inwardly toward the inner edge 107 of the disk
108. A spiral data track 111 disposed on the upper surface 102 of the disk 108 preferably contains a sequence of data storing blocks originating near the inner edge 107 of the disk 108 and spiraling outwardly toward the outer edge 105 of the disk 108. It is to be understood that only a portion of the data band may be formatted to include spiral data tracks, and that this spiral formatted portion may be situated at any radial location on the disk surface. It may be advantageous in other configurations to allocate the entire data band for the purpose of storing multimedia data in spiral data tracks. The portion of a data band formatted to include spiral data tracks for storing multimedia data will hereinafter be defined as the data band portion disposed between an inner spiral diameter location (ISDL) and an outer spiral diameter location (OSDL) on a surface of a data disk 108.

Data tracks 110 and 111 additionally contain a plurality of servo sectors interleaved with the data storing blocks to enable the DASD controller 67 to identify track location and to follow the centerline of the data track. It is noted that various known methods for effectuating data track following using embedded servo sectors are known in the art. It is further noted that only portions of the data tracks 111 and 110 are depicted in FIGS. 15 and 16, and that the tracks are exaggerated in size and configuration for illustrative purposes. It should be understood that a pair of recording data surfaces having oppositely spiraled data tracks need not necessarily be located on opposite sides of the same disk 108. In an alternative configuration, both surfaces of one disk may be formatted with inwardly spiraling data tracks, while both surfaces of another disk may be formatted with outwardly spiraling data tracks.

An important advantage of the spiral data track configuration illustrated in FIGS. 15 and 16 concerns the obviation of the need to perform rapid seek operations, primarily because the video data is formatted in long spiralled data tracks. The novel multimedia DASD 68 normally operates by writing and reading video data progressively along a predefined length of the spiral tracks from beginning to end. As such, the actuator voice coil motor need not perform rapid seek operations typically associated with data storage disks 108 formatted with a plurality of concentric data tracks in accordance with a conventional data storing configuration. Accordingly, the actuator voice coil motor of a novel multimedia DASD 6 is generally considerably smaller than that of a conventional DASD, thereby reducing the cost, weight, and power consumption of the multimedia DASD 68. Improved tracking is also realizable due a substantial reduction in the amount of mechanical vibration and undesirable resonance resulting primarily from the elimination of rapid seek operations.

Further, a conventional DASD employs a spindle motor 114 that is designed to rotate one or more data storage disks 108 at a high rate of speed in order to minimize latency time when accessing data. Latency time is generally understood as a period of delay associated with the amount of time required to rotate a specific data storage area on the disk surface into proximity with a read/write transducer. A spindle motor of a conventional DASD employing 3.5" data storage disks 108, for example, typically rotates the disks at a rate of approximately 5,400 to 7,200 RPM, and represents a major power consuming component of the conventional DASD. In accordance with one embodiment, the spindle motor 114 of the multimedia DASD 68 rotates the disks 108 at nominal rotational rates of 3,600 RPM or lower. Accordingly, a substantial reduction in the size, power consumption, cost, and complexity of a multimedia DASD 68 adapted for providing full VCR-type control over the presentation of a requested multimedia program is realizable.

It is noted that presentation control windows 90 of longer duration will generally require higher disk 108 rotation rates, as indicated by the formatting equations and guidelines developed by the inventors and disclosed hereinbelow. For a relatively low-cost DASD 68, it may be desirable to design the spindle motor 114 to operate at a fixed speed, such as 3,600 RPM, for example. For other configurations employing an air bearing to support the transducer/slider assembly 116, it may be desirable to rotate the disk 108 at a rotational rate sufficient to ensure that a nominal disk-to-transducer clearance distance is maintained on the air bearing. The particular aerodynamic characteristics of the transducer/slider assembly 116 will, of course, become an important factor in determining the nominal flying height of the transducer/slider assembly 116 above the rotating disk 108 and the corresponding desired spindle motor 114 rotation rate. In an embodiment cf the multimedia DASD 68 that employs a lubricant-based system for reducing static and dynamic friction between the disk surface 108 and a constant contact-type transducer/slider assembly 116, disk velocities significantly lower than 1,200 RPM may be advantageous for reducing the size, cost, and power demands of the DASD 68. A load/unload ramp 117 is generally employed to unload the transducer/slider assembly 116 from the lubricated disk surface during periods of extended non-use.

For example, disk 108 rotational rates at or near zero velocity may be desirable during a pause presentation mode. Also, the rotational rate of the spindle motor 114 and disks 108 may be varied depending on the type of multimedia information being buffered by the DASD 68.In such a case, the nominal rate of disk 108 rotation may be determined by the DASD controller 67 or by the set-top controller 64. It is noted that the nominal disk 108 rotation rate may be selected from a range of suitable rotation rates which are typically dictated by the flying characteristics of the particular transducer/slider assembly 116 employed. Also, the optimal portion of the disk data band allocated for storing the video data may be determined by the DASD controller 67. Depending on the particular transducer/slider assembly 116 flying characteristics, the optimal data band location may be situated at an outer diameter disk location, an inner diameter disk location, or an intermediate diameter disk location. It is noted that a nominal disk 108 rotation rate should be appropriately selected to ensure that the output buffer 72 and decoder 74 are provided with a sufficient rate of video data input to assure uninterrupted presentation of the multimedia information. It is further noted that lower disk 108 rotational rates generally correspond to lower sampling rates of the servo information typically embedded between information storing sectors on the surface of the disk 108. As such, a nominal spindle motor 114 rotation rate should be selected to provide a sufficiently high servo information sampling rate.

Another important advantage of the preferred spiral data track configuration illustrated in FIGS. 15 and 16 concerns a significant increase in the linear bit density of a data storage disk 108. The spiral data tracks 110 and 111 are typically narrower than conventional concentric data tracks, thus affording a significant increase in track density for each surface of the disk 108. In a conventional DASD, for example, the width of a data track becomes a limiting factor on the seek time of the DASD. When the actuator performs a seek to locate a new track, it must generally decelerate and settle to a position in which it is following the centerline of the data track. Generally, a longer period of time is required for the actuator to settle at the end of a seek operation for narrower track widths, thereby increasing the overall seek time of the DASD. In accordance with a preferred spiral data track configuration of the novel multimedia DASD 68, no such seek operations are performed, and, as a result, the time required for the actuator 112 to settle is no longer a significant factor that might otherwise limit the degree to which the track width can be reduced.

Another reason increased data density is realizable when storing multimedia data on the disk 108 of a multimedia DASD 68 concerns the relatively low data error rate associated with multimedia data as contrasted to conventionally stored digital data. It is well-understood that even slight alterations to conventional digital data resulting from soft and hard read errors can have adverse results of varying severity. In the case of multimedia data, however, read error rates on the order of several magnitudes higher than those allowable for conventional data are generally acceptable. In many multimedia applications, for example, audio and video information must generally be transferred from the data storage disk 108 to the viewers television 24 or monitor. In general, a read error associated with multimedia data storage in a DASD 68 typically results in only a minor degradation in the quality of the effected audio or video presentation. Many read errors are often imperceivable to the viewing or listening observer. Moreover, various signal processing and smoothing techniques may be employed to enhance the audio and video presentation upon the occurrence of a hard read error, thereby making the hard read error imperceivable to the viewed or listener.

It is therefore possible to substantially increase the data density of a multimedia data storage disk 108 by tolerating higher read error rates. In a preferred embodiment, a 3.5" data storage disk 108 is employed having a linear bit density of approximately 165 Kbpi (Kilobits per inch). It is noted that more data can be stored per linear unit of track length in a spiral data track in comparison to conventional concentric tracks due to increased formatting efficiency. By eliminating the need to perform seek operations, certain information in the data sector headers and servo sectors is no longer needed. In particular, it is possible to eliminate the gray code track identifier in each servo sector which is normally used to identify tracks when performing seek operations in a conventional DASD. It is also possible to eliminate track identifying information in the data servo headers. Although it may still be desirable to include track identifying information at intervals, such as an index mark per disk revolut