Patent Publication Number: US-7907833-B2

Title: Apparatus and method for communicating stop and pause commands in a video recording and playback system

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to controlling video playback systems, and more particularly, to a method and apparatus for communicating stop and pause commands for controlling viewing of moving pictures. 
     In recent years, systems for sending, storing and playing back video information and data from a wide selection of video sources have been developed. These have found widespread use among consumers. In addition to conventional video sources like digital video disks (DVD) and VCRs, video from other sources can be sent, stored and played back to a viewer at the viewer&#39;s convenience. Video sources include cable, satellite and broadcast television sources, as well as the Internet. One example of a commercially available storage and playback system is Personal Television (PTV). PTV refers to the viewing of live television programming in a manner that gives the viewer flexible viewing options, for example, pause and rewind. PTV is also known as Personalized TV, Personal TV Service, File-served Television, Time Delay Recording, Time Shifting and Individualized TV. 
     One of the video playback features highly desired by consumers is generally referred to in the art as “trick play”. The term “trick play” refers to using controls such as pause, instant replay, rewind etc. to control the video presentation. One reason this is referred to as “trick play” is because these operations can be performed while watching live TV in near real time. In order to implement such features, video signals (including live TV signals), are typically stored in a memory device, e.g., a hard drive, before being provided to a display unit for display to the consumer. 
     Another feature desired by consumers is the ability to stop the presentation of a show. The stop command differs from the pause command (also referred to as “freeze”). While both commands typically stop the presentation of moving pictures, the pause command results in display of a still video frame of the motion picture. The stop command stops the presentation but does not display a still video frame of the moving picture. Implementing both the stop and the pause features can be problematic for recording and playback systems. In most cases, the decoder in the display device is not under the control of the recorder and playback system. If the recorder/player stops sending frames in response to both the stop and pause commands, it is difficult for the decoder to distinguish between the stop and pause commands. Furthermore, for a pause command, the decoder is typically unable to determine how many times a particular picture will be displayed. This uncertainty interferes with the display order of the pictures being transferred to the display device. 
     Therefore, a need exists for improved systems and methods for implementing the STOP and PAUSE features for such devices. 
     SUMMARY OF THE INVENTION 
     The invention provides a video recording and playback system comprising a video storing and retrieving device coupled to a video display device so as to provide the video display device with frames of video data for display. The video storing and retrieving device includes at least one memory capable of storing frames of video data, comprising packets according to a format. The format provides a trick mode indicator. A controller is coupled to the memory and controls operations of the memory. A user control device is operable with the controller to allow a user to communicate stop and pause commands to the controller. A processor cooperates with the controller so as to clear the trick mode indicator of at least one retrieved packet in response to the stop command. The processor and controller set the trick mode indicator of at least one retrieved packet in response to the pause command. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of a recording and playback system in accordance with an embodiment of the invention. 
         FIG. 2  illustrates an example of a user operable control device in accordance with an embodiment of the invention. 
         FIG. 3  illustrates an example of a hand held remote user operable control device in accordance with an embodiment of the invention. 
         FIG. 4  is a flow chart illustrating the steps of a method for communicating stop and pause commands according to an embodiment of the invention. 
         FIG. 5  illustrates a Packetized Elementary Stream (PES) including PES Header Flag portion and a PES Header Fields according to an MPEG format suitable for use with the invention. 
         FIG. 6  illustrates a Packetized Elementary Stream (PES) including PES Header Flag portion and a PES Header Fields according to an MPEG format suitable for use with the invention. 
         FIG. 7  is a flow chart for illustrating the steps of a method for receiving stop and pause commands according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Definitions and Examples of Applicable Industry Standards 
     The following terms are defined as used herein. A “system” refers to any collection of communicating elements that performs at least one function. The term “connection” refers broadly to any transport capability to transfer information between two or more end points. Accordingly, the invention is applicable to a wide range of physical networks and systems with different realizations of connections, including bidirectional, one way, and point to multi-point (broadcast) connections. 
     A “command” in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system to perform a particular function either directly or indirectly. Particular functions include those functions performed after either or both of the following a) conversion from one language, code or notation to another language, code or notation; b) reproduction in a different material form. 
     In the context of video playback systems, the following definitions are used herein. The terms “Play” and “Resume” refer to commands that start a presentation, e.g., a movie, from the beginning or resume after stopping or pausing the movie. The term “Stop” means to Stop the presentation of the movie. The term “Pause” means to freeze the picture on the display. 
     Digital television standards suitable for implementing the invention include Digital Video Broadcast (DVB) standards, as well as those described by the ATSC DIGITAL TELEVISION STANDARD, Advanced Television Systems Committee, Doc A/53, Sep. 16, 1995. 
     An example system embodiment employs the MPEG-2 systems and video stream syntax of ISO/IEC 13818-1 &amp; 2, INFORMATION TECHNOLOGY—GENERIC CODING OF MOVING PICTURES AND ASSOCIATED AUDIO INFORMATION, International Standards Organization, 1995, Sep. 16, 1995. In particular, the ATSC DIGITAL TELEVISION STANDARD describes a model for a hypothetical ancillary services target system decoder for a DTV receiver. 
     The International Standards Organization provides “Digital Storage Media Command and Control (DSM-CC)” standards. This standard provides for certain client/server operations such as video control (backward, pause, etc.), video transmission, and video service discovery. 
     In 1998, this standard was extended and became Part 6 of the current MPEG-2 standard. DSM-CC itself is not developed for datacast, but some parts of DSM-CC, e.g., the Data Download Protocol, DSM-CC sections (a packet encapsulation on top of the PES), and the basic scheme of its service discovery, are adopted by both ATSC and DVB datacast standards. 
     The DVB standards disclose a DVB signal to be carried over a range of bearer networks. Various standards have evolved which define transmission over particular types of links. These standards include: DVB-S (Satellite); ETS 300 421 (Digital Satellite Transmission Systems); DVB-T (Terrestrial) ETS 300 744 (Digital Terrestrial Transmission Systems); Interfaces to Plesiochronous Digital Hierarchy (PDH) networks (prETS 300 813); Interfaces to Synchronous Digital Hierarchy (SDH) networks (prETS 300 814); Interfaces to Asynchronous Transfer Mode (ATM) networks (prETS 300 815); Interfaces for CATV/SMATV Headends and similar Professional Equipment (EN50083-9). 
     Each of the above standards is readily available in the literature and the contents thereof are familiar to those of ordinary skill in the art. 
     
       FIG. 1 
     
     General System Description 
       FIG. 1  is a simplified block diagram of a video system  100  according to an embodiment of the invention. As illustrated in  FIG. 1 , system  100  comprises a sender  150  capable of communicating with a receiver  190 . Sender  150  provides a packetized data stream  195  to receiver  190  via a communication link. Packetized data stream  195  transports video images, for example, a plurality of successive video frames comprising a moving picture for display on a display device  120 . Receiver  190  is capable of receiving packetized data stream  195  including the video images and displaying the images on a display  120 . System  100  further includes at least one user operable control device  160 . User operable control device  160  is capable of communicating user commands to sender  150  to control the display of images on display  120 . In one embodiment of the invention, user operable control device  160  is provided on a front panel of a housing of sender  150 .  FIG. 2  is an example of a suitable user operable control device  160  implemented on a front panel of the main body of a DVD video recorder/player. 
     In another embodiment of the invention, user operable control device  160  comprises a remote user operable control device, for example, a conventional hand held remote control device.  FIG. 3  illustrates a conventional hand held user operable control device according to an embodiment of the invention. Such devices typically communicate user commands via electromagnetic or infrared radiation to sender  150  as is known in the art. As those of ordinary skill in the art will readily appreciate, there exists a wide variety of user control devices of various shapes, sizes and communicating protocols, for controlling recording and playback systems. The present invention is capable of implementation using any of these conventional devices. 
     In one embodiment of the invention, video system  100  is implemented at least in part by a personal video recording system (PVR). In another embodiment of the invention, video system  100  is implemented, at least in part, by an integrated television system such as an integrated High Definition Television (HDTV) system. Integrated HDTV systems are manufactured with both the HDTV monitor and HDTV tuner in a single unit. 
     For purposes of explanation and example,  FIG. 1  illustrates one each of sender  150 , receiver  190  and display device  120 . In practice however, it is contemplated that any number of such senders, receivers and displays will be included in system  100 . For example, embodiments of system  100  include one or more senders  150  communicating with one or more receivers  190  within a household or for a plurality of households and subscribers. 
     As those of ordinary skill in the art will readily appreciate upon reading this specification, the invention is capable of implementation in a variety of video system environments, including non-homogeneous hardware and software environments. Accordingly, an embodiment of video system  100  can be described broadly as comprising a client i.e., a consumer of multi-media content and a server, i.e., an entity that provides multi-media content and services. In an embodiment of the invention, system  100  comprises a distributed system and includes multiple computing platforms, including video systems (sometimes referred to as “pumps”)  130  providing video, for example, a video on demand service. In one embodiment of the invention, sender  150  is implemented in a “client” of such a system  100 . In an alternative embodiment of the invention, sender  150  is implemented in a server of such a system. 
     System  100  is capable of implementation in networks that support Digital Storage Media Command and Control (DSM-CC). DSM-CC is a standard for the delivery of multimedia broadband services. DSM-CC is defined in part 6 of the MPEG-2 standard (MPEG-2 ISO/IEC 13818-6 Extensions for DSM-CC) and is known to those of ordinary skill in the art. DSM-CC embodiments include Hybrid Fiber Coax (HFC) and Fiber to the Curb (FTTC) embodiments. In one embodiment of the invention, HFC network connections are realized using an MPEG-2 TS in the downstream (Server to Client) direction and a packet contention scheme in the other direction. Other embodiments of the invention include FTTC networks realizing connections as bi-directional ATM Virtual Channel Connections (VCC&#39;s). In an embodiment of the invention, sender  150  is connected to a standard ATM backbone network while receiver  190  client connects to an access network (such as HFC or FTTC). 
     User Commands 
     Regardless of the complexity of the particular implementation, system  100  includes a user operable control device  160  capable of communicating a plurality of playback control commands to sender  150 . In one embodiment of the invention, these commands include “trick mode” commands. The plurality of user commands includes at least two types of commands. A first type of command is a type that causes display device  120  to stop displaying video images. An example of this type of command includes the “stop” command, as generally known in the art. However, the particular name given to the first type of command is not intended to limit the invention. The first type of command is any command that results in stopping the presentation of video images on display device  120 . All commands of this type are considered first type commands and are within the scope of the invention, regardless of command name in any language, and regardless of how the stopping is accomplished. 
     According to one embodiment of the invention, user commands further include a second type of command. The second type of command is one that is intended to cause repeated display of the same video image on display device  120 . Examples of second types of commands include “pause”, and “freeze” commands. As stated above, the command name is not intended to be limiting of the invention. Any command that causes repeated display of the same video image on display device  120 , thereby creating the impression of a still image, is a second type of command. 
     The first type command and the second type command are intended to have different display effects on system  100 . Existing MPEG standards include a format that allows implementing a freeze (pause) command in trick mode. However, most devices presently available with trick mode capability don&#39;t continue to send packetized video streams to the display decoder (for example, receiver  190 ) in freeze mode. Instead, these devices stop sending the MPEG stream. Central Processing Unit (CPU) bandwidth can be conserved in this manner. Nevertheless, this practice presents difficulties for the decoder in receiver  190 . That is, both types of commands result in stopping data input to the frame decoder of receiver  190 . In such systems, the frame decoder portion of receiver  190  is not typically under control of user operable control device  160  and does not directly receive user commands from device  160 . Therefore, the frame decoder of receiver  190  cannot determine which command caused the data input to stop. 
     Inventive Solution 
     A solution to the problem described above is provided by a method and apparatus according to an embodiment of the invention. According to one embodiment of the invention, when sender  150  receives a command from user operable control device  160 , sender  150  responds by providing at least one corresponding command indicator in packetized data  195 . Packetized data  195 , including the at least one command indicator, is then provided by sender  150  to receiver  190 . Based upon the at least one command indicator, a command decoder of receiver  190  determines the command type, and specifically, determines whether the command is a first type command or a second type command. Therefore, receiver  190  can distinguish between first type and second type commands, and respond appropriately even when packetized data stream  195  stops for both command types. 
     Detailed System  100  Description 
       FIG. 1  illustrates logical and functional components of a video system  100  according to one embodiment of the invention. The illustrated functions and components are capable of implementation in hardware, software and various combinations thereof. Furthermore, the functions of video system  100  as illustrated in  FIG. 1  are combinable and distributable over physical system components. Furthermore, functions are capable of combining and housing in a single physical enclosure or they may be distributed over two or more separate enclosures and operatively interconnected by wires, cables, wireless or other signal conveying means. Regardless of implementation, one embodiment of system  100  comprises at least one sender  150 , at least one receiver  190 , and at least one user operable control device  160 . 
     Sender  150   
     General 
     Sender  150  stores and retrieves moving pictures in any MPEG-2 compliant packet format. Products and technology, and associated implementation standards, are available for encoding and transmitting an MPEG-2 compliant video stream from a video content source ( 130 ,  131   132 ) to sender  150  over a variety of links. These include: Radio Frequency Links (UHF/VHF); Digital Broadcast Satellite Links; Cable TV Networks; Standard Terrestrial Communication Links (PDH, SDH); Microwave Line of Sight (LoS) Links (wireless); Digital Subscriber Links (ADSL family); and Packet/Cell Links (ATM, IP, IPv6, Ethernet). 
     Therefore, sender  150  is capable of implementation in a variety of commercial systems. These include Personal Video Recorders (PVR), Digital VCRs, Digital Video Recorders (DVR), Digital Videocassette Recorders, Personalized TV Playback Devices, Digital Disk Recorders, Home Media Servers, Personal Computers, Virtual VCRs, IP Media Appliances, Digital Network Recorders, Digital Videotape Recorders and Videodisc Recorders and Players. 
     In one embodiment of the invention, sender  150  includes at least one input  241  for receiving a video signal from a video content source. Examples of suitable video content sources include video pump  130 , broadcast station  131 , cable headend  132  and internet portal  133  and further include the sources identified above. The video signal received at input  241  includes images to be played back on a display device  120 . Commercially available hardware and software is readily available for delivering video signals from these sources, decoding the signals and delivering the signal to the input of a recording device. 
     Sender  150  further includes at least one video storage device  210  for storing at least a portion of the video images to be played back, and at least one video output  275  for providing video images, in packetized format, to receiver  190  for display. The operation of sender  150  is at least partially controllable by a user in accordance with the user commands described herein including at least a first type of command and a second type of command. Sender  150  further includes at least one processor  220  for receiving and encoding user commands including at least stop and pause commands, from user operable control device  160 . 
     Input  241   
     As will be appreciated further from the following discussion, input  241  is capable of receiving MPEG-2 compliant video signals from at least one of a variety of video content sources. Suitable video content sources include, analog and digital TV broadcasting systems, cable and satellite television systems, video and film production systems, multi-point video conferencing systems, digital video recording applications, real-time video transport systems, video monitoring systems, law enforcement and public safety applications, video encoding and editing systems and broadband video on-demand (VOD) systems. 
     A variety of suitable communication links, including analog and digital communication links exist and are suitable for implementing the invention. Some examples include, but are not limited to, T1/E1 and Ethernet/IP (Internet Protocol) links, broadcast television over the Internet (TV over IP), Integrated Service Digital Networks (ISDN), Public Switched Telephone Networks, cable television networks including cable head-end links and subscriber networks, satellite links, microwave and power line communication links, fiber optic links and wireless communication links. In one embodiment of the invention, MPEG compatible input video streams are received at input  241 . In one embodiment of the invention, input  241  is capable of receiving a radio frequency carrier modulated responsive to a Motion Picture Experts Group (MPEG) compatible signal. Video signals suitable for the invention include digital and analog signals in compressed and uncompressed formats. 
     Functions of Sender  150   
     In one example embodiment of the invention, sender  150  is an integrated Digital Video Broadcast (DVB) receiver capable of receiving, demultiplexing and decoding MPEG signals. In another example embodiment of the invention, MPEG compatible input video streams are received at input  241 . Sender  150  demodulates and processes the received signal in accordance with MPEG standards. 
     Examples of MPEG standards suitable for use in system  100  include those recommended by ISO/IEC JTC 1/SC29/WG11 (International Standardization Organization/International Electrotechnical Commission Joint Technical Committee 1/Sub Committee 29/Working Group 11) for storing video in digital storage media (DSM), for example storage media  212  of sender  150 . Other suitable standards include the MPEG-2 standard for high definition digital broadcasting such as EDTV (Enhanced Digital Television) and HDTV (High definition Television). 
     In one embodiment of the invention, a carrier modulated according to known methods includes MPEG compatible signals and is received by sender  150  via input  241 . Sender  150  tunes to the frequency in which programs to be recorded and played back are multiplexed, and demodulates and error corrects bit streams corresponding to selected programs. In an embodiment of the invention, sender  150  converts a received bitstream into a transport stream (TS) defined by MPEG2 system, and demultiplexes an audio or video PES packet of a program from the TS and outputs a PES packet to storage subsystem  150 . 
     In another embodiment of the invention, sender  150  receives analog signals via input  241 . In such an embodiment, sender  150  digitizes, encodes and, in some embodiments compresses the analog video signal. An embodiment of the invention includes a decoder according to the conceptual model for a transport stream system target decoder (T-STD) described in the ISO/IEC 13818-1:1996 (MPEG-2) standard. The MPEG-2 conceptual T-STD model comprises an individual system target decoder for each of the elementary data streams representing the video, audio, and system information components of a television program. In that embodiment, sender  150  receives the television program information and provides a digitally encoded, compressed video stream compatible for recording onto storage medium  212  by storage device  210 . 
     In one mode of operation, sender  150  continuously digitizes, compresses and stores video signals received via input  241 . For example, sender  150  receives programming during a time interval selected by a user. Sender  150  compresses and encodes the program video and provides compressed video to storage device  210  for temporary storage on storage medium  212 . During playback, sender  150  retrieves the compressed data from storage medium  212  and decompresses and decodes the video. 
     In yet another embodiment of the invention, sender  150  receives and encodes real time streams of television and video and provides the encoded streams to video storage medium  212  for near real time playback and viewing on display  120 . 
     In one embodiment of the invention, sender  150  is implemented in a cable television set top box (STB) capable of receiving video images via video input  241  from a cable network distribution system. In another embodiment of the invention, sender  150  is implemented in a satellite receiver capable of receiving video images via video input  241  from a satellite downlink, receive antenna or other video signal supplying means. 
     In one embodiment of the invention, sender  150  is housed in a local tuner/receiver, that is, sender  150  is physically located within a broadcast or cable video tuner/receiver (not shown) at a viewer&#39;s site, for example at a viewer&#39;s home, along with receiver  190  and display  120 . In one embodiment of the invention, sender  150  includes a media player, for example a digital video disk (DVD) player for playing back video images from a storage medium such as digital video disk. (DVD) In that case, input  241  is in communication with a storage device controller  283  that provides images from storage medium  212  in accordance with user commands. 
     In an alternative embodiment of the invention, sender  150  is a remote sender, for example, located at a cable headend site, or on board a satellite. In that case, sender  150  is capable of receiving and responding to commands from a remote user operable control device  160 , for example, via a satellite uplink, Out of Band (OOB) communications channel, or another suitable communications uplink. At present, trick play commands are precluded from transmission in a broadcast MPEG stream. However, this is a regulatory constraint and a not a restraint imposed by the available technology for implementing bidirectional communications between user operable control devices and other system components. 
     In another embodiment of the invention, system  100  includes Interactive Video on Demand (IVOD) capability. IVOD Is an extension of VOD (Video on Demand) in which trick play functions such as fast forward, fast rewind, and pause are implemented. One IVOD system implementation of the invention includes three components: (1) sender  150  comprising the user&#39;s “Set-top Box”, (2) the network providing input at input  241  (3) servers  130  with archives of movies (or whatever the server is offering to show.) The consumers communicate with the IVOD server via their set-top boxes. 
     Storage Device  210   
     Sender  150  provides selected, received and processed video signals for storage by storage device  210 . In one embodiment of the invention, sender  150  provides signals in accordance with a DSM-CC (Digital Storage Media-Command and Control) ISO/IEC standard for the delivery of multimedia broadband services. DSM-CC is defined in part 6 of the MPEG-2 standard (MPEG-2 ISO/IEC 13818-6 Extensions for DSM-CC). Storage device  210  records the audio or video PES packet input onto storage media  212 . 
     In embodiments of the invention wherein system  100  comprises a Personal Video Recorder (PVR), sender  150  typically includes the circuits of the PVR that compress the signal of, for example, a live TV show, and save the show on storage medium  212 . Sender  150  subsequently, in one embodiment with about a 0-3 second delay, provides the stored show to receiver  190  for display to a viewer. In that case, the viewer is watching the video from storage medium  212 , not directly from the antenna, satellite or cable connection at input  241 . 
     In another embodiment, the PVR receives an already digitally encoded signal. In that case sender  150  stores the encoded signal. Examples of encoded video signal sources include, but are not limited to, cable headends, satellites, digital video broadcast sources, etc. 
     In one embodiment of the invention, storage medium  212  is temporary, for example, a buffer memory. Examples of other suitable storage medium  212  include semiconductor memories, optical storage media, magnetic storage media, and any media capable of storing compressed video signals. When playing back the stored encoded digital signal, sender  150  provides the stored digitally encoded signal to receiver  190 . Generally, storage medium  212  is any storage medium suitable for storing video information. 
     In one embodiment of the invention, storage medium  212  is suitable for storing an audio or video PES packet included in a MPEG2 transport stream. Suitable storage media include both removable and fixed storage media and digital storage media (DSM), for example, read-only DVD video (or DVD-ROM), write-once DVD-R, recordable/readable DVD-RW (or DVD-RAM), hard disk drives, optical storage media and the like. Exemplary embodiments of storage medium  212  include DSM implemented as random access memory logic as well as hard disk drives. Commercially available hardware is adequate for use in the invention. 
     The DVD video (DVD-ROM) standards support MPEG2 as a moving picture compression scheme in accordance with the MPEG2 system layer. Furthermore, DVD video standards are configured by adding presentation control data (navigation data) for fastforward, rewind, data search, and the like. In an embodiment of the invention storage media  212  is formatted according to a standard supporting the UDF Bridge format (a hybrid of UDF and ISO9660) thereby allowing computers to read the stored data. 
     Processor  220   
     In addition to storage device  210 , sender  150  includes a storage device controller  283  and processor  220 . Commercially available storage device controllers include one or more processors. Typical commercial controllers include circuits operatively coupled to input  241 , user operable control device  160  and storage device  210  for controlling recording and playback of the video information to and from storage media  212 . For example, in an embodiment of the invention, controller  283  analyzes the incoming MPEG video stream and controls writing to storage medium  212 . Processor  220  is representative of a processor that implements an inventive command encoder according to an embodiment of the invention. Those of ordinary skill in the art will recognize that the actual processor employed to implement processor  220  of the invention is locatable in controller  283 , as well as in other circuits of sender  150 . Further, it is anticipated that embodiments of the invention will implement the functions of processor  220  in a distributed manner. 
     User Operable Control Device  160   
     User operable control device  160  cooperates with processor  220  to permit a viewer to control recording and retrieval of video images to and from storage media  212 .  FIG. 2  is an example of a suitable user operable control device  160  implemented on a front panel of the main body of a conventional set top box. Fundamental operations are made by user operation of control keys  161  and  162 . For example, user activation of STOP key  162  stops the video presentation. User activation of PAUSE key  161  pauses, or freezes, the presentation. Embodiments of the invention include front panels of DVD video recorders incorporating basic operation keys such as a power switch button, open/close key, playback key, stop key, chapter/program skip key, rewind key, fast forward key, recording start button (not shown), and the like. 
     In one embodiment of the invention, various fundamental operations are performed by user operation of a remote controller  300  as illustrated in  FIG. 3 . STOP and PAUSE commands are performed by user activation of PAUSE key  361  and STOP key  362 . 
     Regardless of the source and device employed to provide the STOP and PAUSE user commands, the invention provides the capability for communicating STOP and PAUSE commands from sender  150  to receiver  190 . In an embodiment of user operable control device  160 , the operation of the STOP and PAUSE keys are as follows. When STOP key  162  is pressed during disc playback or recording, playback or recording is stopped. When PAUSE key  161  is pressed during playback a video frame in the program chain currently being played back is displayed as a still image. 
     According to embodiments of the invention, receiver  190  is capable of distinguishing the STOP and PAUSE commands. Further, receiver  190  can distinguish the commands even when sender  150  stops providing video frames to receiver  190  in both the STOP and PAUSE modes of operation. 
     User Command Encoding 
     In a playback mode of operation, storage device  210  provides PES packets stored in storage medium  212  comprising video packets  195 . When sender  150  receives a command, for example, a command for normal play or trick play from user operable control device  160 , processor  220  encodes an indication of the user-entered playback command for normal play or trick play into the PES packets provided by storage medium  212 . For example, when the command is a trick play command, controller  284  provides packets from storage medium  212  having a trick play indicator indicating trick play mode and sends the packets in video packets  195 . In conventional systems, the indicator is a trick mode bit that is typically set for trick mode data packets. According to the invention, a command encoder at the output of memory medium  212  determines the setting of the trick play indicator of packets retrieved from memory. A processor, for example, processor  220  operates on the trick play indicator in accordance with the methods described herein. 
       FIG. 4  illustrates a flow chart of a processing method employed by processor  220  to implement, in cooperation with controller  283 , a command encoding feature according to an embodiment of the invention. It will be appreciated that the flow chart of  FIG. 4  illustrates but one advantageous encoder implementation and that other encoder implementations may also be used. 
     According to an example of the invention in use, a user initiates a command via a user operable control device, for example the device shown in  FIG. 1  at  160 . According to step  410  the user command is received. In an embodiment of the invention the command is provided to storage device controller  283 . The command is processed by a processor to determine if the command is a Stop command, as indicated by step  420 . In one embodiment of the invention, the aforesaid processor is included in storage device  210 , e.g., in memory controller  283 . In an alternative embodiment of the invention, the processor is an additional processor, e.g., processor  220 . Regardless of where the processor is located, if the processor determines the received command is a STOP command, the processor encodes a stop command by operating upon at least one packet retrieved from memory medium  212 . In one embodiment, in response to a Stop command, processor  220  ensures a trick mode flag in at least one of the packets retrieved from memory medium  212  is cleared, and forwards the at least one packet including the cleared flag to receiver  190 . 
     On the other hand, if the processor determines the command issued by a user is not a STOP command, the processor further determines if the command is a PAUSE command as indicated at step  430 . If the processor determines the command is not a PAUSE command the processor proceeds with another operation as illustrated by step  440 . In that case, no further action is to be taken by the processor regarding the trick mode flag and the trick mode field of the PES packets. Other operations include executing a command other than stop or pause. The process end is illustrated at  499 . 
     If the processor determines the command issued by a user is a PAUSE command, the processor encodes the pause command in a retrieved packet by setting a trick mode flag of a retrieved packet to 1 and further insures the trick mode field is set to indicate a freeze mode, as illustrated in step  450 . In one embodiment of the invention, the trick_mode_control field is set to indicate freeze mode according to the settings shown in Table 2 below. 
     In one embodiment of the invention, when the Pause command is generated by the user operable control device, sender  150  obtains Intra picture (I picture) information from storage device  210  and instructs transfer of the I picture data to the PES packets for repeated display of an I frame on display  120 . 
     Packetized Data  195   
       FIG. 5  illustrates a format of an example packet  500  of video packets  195  according to an MPEG compliant embodiment of the invention. Example packet  500  is organized into a plurality of fields  510 - 590 . According to an MPEG compliant packet format, a Primary Elementary Stream (PES) packet data block field  590  is followed by a PES header field  580 , a PES Header length field  570 , a PES header flag field  550 , and other fields  540 - 510 , as described in MPEG packet format specifications readily available in the art. 
     PES header flag field  550  comprises a plurality of indicator fields, i.e., flags  551 - 562 . In particular, in an embodiment of the invention, Trick Mode TM flag  559  indicates the operating mode of storage device  210 , as shown in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 Trick Mode (559) 
                 Indicates the presence of an 8 
               
               
                   
                 (DSM_trick_mode_flag) 
                 bit field describing the DSM 
               
               
                   
                   
                 (Digital Storage Media) operating 
               
               
                   
                   
                 mode: 
               
               
                   
                   
                 1 - Field is present. 
               
               
                   
                   
                 0 - Field is not present. (For 
               
               
                   
                   
                 broadcasting purposes, set = 
               
               
                   
                   
                 0.) 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 6  illustrates PES header fields  580  of packet  500 . As shown, fields  580  comprise a plurality of fields  581 - 586  representing the Presentation Time Stamp (PTS), Decode Time Stamp (DTS), and Elementary Stream Clock Reference (ESCR), ES rate of twenty two bits, additional copy information of seven bits, previous PES Cyclic Redundancy Check (CRC) of sixteen bits and PES extension control. 
     In particular, a DSM trick mode control field  582  comprises eight bits of data. 
     DSM trick mode field  582  is used to indicate that a video stream originally stored on recording media (e.g.,  212  of  FIG. 1 ) is subjected to trick mode reproduction and differs from the corresponding source bit stream received at input  241  by sender  150 . Table 2 describes DSM_trick_mode field  582 . 
                                 TABLE 2                          DSM_trick_mode   An eight bit field indicating the nature               of the information encoded. The field               is further partitioned as follows:               trick_mode_control (3 bits),               field_id (2 bits),               intra_slice_refresh (1 bit), and               frequency_truncation (2 bits).           trick_mode_control   Indicates the nature of the DSM Mode:               000 - Fast Forward               001 - Slow Motion               010 - Freeze Frame               011 - Fast reverse               1xx - Reserved.                        
Receiver  190 
 
     Receiver  190  includes an input  194  for receiving packetized data  195  including a command indicator from sender  150 . Receiver  190  processes the video data in the packetized data stream and converts the video data to a form suitable for presentation on display device  120 . 
     Decoder 
     Receiver  190  includes a processor  184  for implementing a decoder  252  for determining if a user has given a Stop or Pause command to sender  150 . Processor  184  is informed by means of a 1 bit flag (DSM_trick_mode_flag) in the PES packet header indicating that the bitstream is reconstructed by DSM in trick mode, as described above, and in particular, as modified by sender  150  according to the principles of the invention. When the DSM_trick_mode_flag is set, an 8 bit field (DSM_trick_modes) follows. According to one embodiment of the invention, this field is encoded according DSM_trick_modes semantics defined in the ISO/IEC 13818-1. D.11.1, and further encoded by sender  150  of the invention to indicate Stop and Pause commands. Processor  184  decodes the bitstream and displays it according to DSM_trick_mode, if any, identified in the 8 bit trick mode field ( 582  of  FIG. 6 ). According to one embodiment of the invention, If the DSM trick mode field contains a PAUSE code, a video decoder of receiver  290  decodes the picture and displays the latest received I frame until the next picture is decoded. 
     In that way, processor  184  comprises a decoder  252  for determining a user command based on a command indicator. Processor  184  makes this determination, at least in part, by detecting the state of the command indicator in the packetized data stream. Receiver  190  cooperates with display device  120  to display video images in accordance with the user command determined by processor  184 . 
     Therefore, processor  184  implements a method for decoding video data packets so as to distinguish a stop command from a freeze command.  FIG. 7  is a flow chart that illustrates exemplary modes of operation of receiver  190  as it displays the video corresponding to packetized data  195 . It will be appreciated that the flow chart of  FIG. 7  illustrates but one advantageous implementation and that other implementations are envisioned. 
     As discussed above, typical displays include a video decoder  185 . However, the invention further includes an apparatus and method for decoding Stop Pause commands based on the status of the TM flag in received packets. A processor  184  has access to the packetized data provided by sender  150  such that it can provide the data contained therein to a video stream decoder. Similarly, processor  184  also has access to the frame index data structure such that processor  184  can use this information to facilitate implementation of TrickPlay of the video stream data. 
       FIG. 7  Receiving 
       FIG. 7  is a flow chart illustrating a method for receiving trick mode commands according to one embodiment of the invention. The method begins at step  710  when receiver  190  is receiving video data  195  from sender  150  as illustrated in  FIG. 1 . 
     According to step  720 , receiver  190  checks frame decoder  252  to determine if frames are being decoded. As long video data packets  195  are decoded, processor  184  updates a trick mode flag  188 . Trick mode flag  188  is implemented in receiver  190 . In one embodiment of the invention, trick mode flag  188  is a specified bit in a memory of receiver  190 . 
     According to step  740 , processor  184  updates receiver trick mode flag  188  to reflect the state of the trick mode flag of respective received packets. As long as the trick mode flag field of the received packets is set, receiver trick mode flag  188  is set and the bits in trick mode field of data stream are decoded. In that case, processor  184  determines the designated trick play based on the contents of the bits in the field, and an indication of the trick mode, i.e., Fast Forward, Slow Motion, Freeze Frame and Fast Reverse, is provided via mode indicator  183  as indicated by step  744 . 
     On the other hand, if data input to frame decoder  252  stops, step  720  continues with step  722 . That is, when data is not present, the last trick mode flag  188  is checked. If the last trick mode flag  188  is set, mode indicator  183  is checked. If mode indicator  183  indicates “freeze frame”, a Pause command is detected and a last received frame of data is repeatedly displayed on display  120 . In one embodiment of the invention, the last received Intra coded reference frame (I frame) is repeatedly displayed. 
     In the event no data is present as per step  720  and the “last trick mode” indicator  188  is not set (i.e., the flag is cleared), then a Stop command is detected. In that case, a last received frame of data is not repeatedly displayed on display  120 . 
     In light of the foregoing description of the invention, it will be recognized that the present invention can be realized in hardware, software, or a combination of hardware and software. Communicating according to the present invention can be realized in a centralized fashion, or in a distributed fashion where different video processing elements are spread across several interconnected systems. Advantageously, in such an entertainment system, the information file can be used to communicate information between independently and remotely located MPEG decoders. Any kind of computerized or digital MPEG processing system, or other apparatus adapted for carrying out the methods described herein, is suited. 
     Although the present invention as described herein contemplates a CPU  122  of  FIG. 1 , a typical combination of hardware and software can further include a general purpose computer system with a computer program that, when being loaded and executed, controls the digital video recording and playback system similar to the control section  120  of  FIG. 1 , such that it carries out the methods described herein. The present invention can also be embedded in a computer program product which comprises all the features enabling the implementation of the methods described herein, and which when loaded in a computer system is able to carry our these methods. 
     The description above is intended by way of example only and is not intended to limit the present invention in any way, except as set forth in the following claims.