MXPA06000812A - Exploitation of discontinuity indicator for trick mode operation - Google Patents

Abstract

A system and a method for modifying a stream of multimedia content to implement trick mode playback functions in MPEG receivers that do not follow general MPEG trick mode implementation recommendations. The system can include a processor that sets a discontinuity indicator in an adaptation field associated with a video frame. A substitute program clock reference (PCR) value also can be set in the adaptation field. The substitute PCR value can be set to a value approximately equal to a presentation time stamp (PTS) of the video frame with which the adaptation field is associated. The processor also can insert an adaptation field with at least one video frame with which an adaptation field was not already associated. The processor also can remove at least one video frame from the stream of multimedia content. Adaptation fields associated with the removed video frame also can be removed.

Description

European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, For two-letter codes and other abbreviations. Refer to the "Guid- FR, GB, GR, HU, IE, IT , LU, MC, NL, PL. PT, RO, SE, YES, an e Notes on Codes and Abbreviations "appearing ai the begin- SK, TR), OAPI (BF, BJ, CF, CG, Cl, CM, GA , GN, GQ, no ofeach regular issue afilie PCT Gazette .GW, ML, MR, NE, SN, TD, TG). Published: - with intemalional search repon USING THE DISCONTINUITY INDICATOR FOR A TRICK MODE OPERATION CROSS REFERENCE WITH RELATED APPLICATIONS This application claims the benefit of the Patent Application of United States Serial No. 60 / 488,835, filed July 21, 2003, which is hereby incorporated by reference in its entirety.

GOVERNMENT RIGHTS ON THE INVENTION Not applicable.

FIELD OF THE INVENTION Inventive arrangements are generally related to video systems and more particularly to systems that perform trick-mode operations on multimedia content streams.

BACKGROUND OF THE INVENTION Multimedia content is often encoded in digital form in a compressed format in order to minimize the amount of storage necessary to store the multimedia content and to minimize the amount of bandwidth necessary to broadcast the content. multimedia content to the viewers. One format of digital compression that is very popular today is the format of Moving Pictures Expert Group (MPEG).

Typically, digital television transmission systems transmit the MPEG encoded multimedia content to digital television receivers, which decode the MPEG stream for display in a display, such as a television. MPEG streams contain clock references (PCR) that are associated with each frame and are delivered in what is called the adaptation field. The PCRs are count values based on a 27 MHz clock contained within an encoder - called a system synchronizer clock (STS) - which encodes the MPEG current. The PCRs are used to synchronize the synchronizer clock of the local decoder system (LSTC) with the STS of the encoder. MPEG streams often also contain a presentation time stamp (PTS) for each picture encoded in the MPEG streams. The PTS indicates the instant in which a coded image or an audio block must be removed from the receiver's buffer, instantly decoded and presented for display. When viewing multimedia content received in an MPEG stream, some viewers may wish to perform certain trick modes. A trick mode can be a multimedia playback where playback is not performed at a normal speed or in an advanced direction. The examples of trick mode are overtake, delay, pause, etc. When a trick mode is performed on a media content decoded from an MPEG stream, it is recommended that the decoder ignore the PCR values and decode and display the frames as they become available.

To implement this process, a DSM_truco_mode_label tag is set to 1 within each packed elementary stream (PES) of the MPEG stream that is processed during trick mode playback. When the DSM_truco_mode_label is set to 1, it is generally recommended that the decoder deny the values of vbv_retraso_ and temporal_reference, and then decode each image, the display until the next image is decoded. The vbv_retraso is an unsigned 16-bit integer representing the number of 90 kHz clock periods between entering an image start code into the buffer and removing and decoding the entire image. The value of temporal_reference indicates the order in which the intra-MPEG images, predicted images and bidirectional images should be displayed (tables 1, P and B, respectively). Some of the digital television receivers, such as the receivers of Advanced Television Systems Committee (ATSC), do not follow the general recommendation. Consequently, such non-compatible receivers try to use the PTS and PCR values of the bitstream to decode and display the video. In accordance with this, these non-compatible receivers implement the reproduction of the trick mode.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a system and method for modifying a stream of multimedia content to implement the trick mode playback functions on MPEG receivers that do not follow the implementation recommendations of MPEG trick mode, such as the receivers of the Advanced Television Systems Committee (ATSC). The system may include a processor that adjusts a discontinuity_indicator in an adaptation field associated with a video frame. The processor also adjusts a substitute program clock reference (PCR) value in the adaptation field. The substitute PCR value can be adjusted to a value approximately equal to a presentation time stamp (PTS) of the video frame with which the adaptation field is associated. In addition, the processor can insert an adaptation field with at least one video frame with which the adaptation field was not associated. The processor can also remove at least one frame of adaptation of the stream of multimedia content. The adaptation fields with the video frame removed can also be removed.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the present invention will be described below in more detail, with reference to the accompanying drawings, in which: Figure 1 shows a block diagram of a system, which is useful for understanding the present invention. Figure 2A shows a portion of an MPEG stream, which is useful for understanding the present invention. Figure 2B shows a modified version of the MPEG stream of Figure 2A. Figure 3 shows a sync circuit of the MPEG decoder useful in understanding the present invention. Figure 4 shows a flowchart useful for understanding a mode of the present invention, which implements forward reproduction.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for performing trick mode operations with the use of a digital television receiver that is not pre-configured for such operations. The trick mode operations are implemented by manipulating the time information within a delivered stream of the multimedia content to control an amount of time each video frame (frame) is stored within a stream. More particularly, the adaptation fields can be added in a stream of Moving Pictures Experts Group (MPEG). The discontinuity indicators in the adaptation fields can be adjusted to indicate discontinuity in an MPEG stream.

In addition, the program clock references (PCR) contained in the adaptation fields can be set to substitute values that cause the MPEG current to be reproduced to change in accordance with the desired trick mode, as will be described in more detail below. . Accordingly, the trick mode playback functions can be implemented on MPEG receivers that do not follow the general recommendation of the MPEG trick mode implementation, such as the Advanced Television Systems Committee (ATSC) receivers. Figure 1 shows a block diagram of a system 100 useful for understanding the present invention. The system 100 may include a display 190, a storage device 150 and an MPEG receiver 110. MPEG receivers are known to those skilled in the art. A receiver is a receiver of the Advanced Television Systems Committee (ATSC), which may also include the 190 display as a complete element. In a typical arrangement, the MPEG receiver 110 may comprise a tuner 115 to selectively receive a current 120 MPEG. For example, the tuner 115 can be connected in communication with an antenna, a cable television system, the Internet or with any other device or system, which can provide the current 120 MPEG for the tuner 115. The MPEG receiver 110 can also include an entry 140 of the user who can receive user input commands, for example from a keyboard, a remote control interface and / or any other user interface device. The user's input commands can be propagated to the components within the MPEG 110 receiver that processes the user's commands. For example, user commands may be propagated to the tuner 115. User commands may also be propagated to a storage device 150 to initiate various operations of the storage device, such as data storage and trick mode operations. In addition, the MPEG receiver 110 may include a decoder 125 MPEG for decoding the 120 MPEG stream in uncompressed audio / video streams for display in a display 190. The MPEG decoder 125 may include a sync circuit 130, which will be described later with reference to Figure 3. Such decoders 125 are known to those skilled in the art. The MPEG decoder 125 may be linked in communication with a communication port 135. The communication port 135 can be any port suitable for bi-directional communication of the MPEG streams between the MPEG receiver 110 and one or more devices. For example, the communication port 135 may be connected in communication with the storage device 150, which may also include a communication port 155 that supports bi-directional communication of the MPEG streams. In one arrangement, the communication port 135, 155 may be an IEEE-1394 (FireWire) port or a universal serial bus (USB) port that is operatively connected. The storage device 150 may also comprise a processor 160 for processing the MPEG streams; a data storage 170 for storing the MPEG streams and a recording / playback interface 165 for interfacing the data storage 170 with other components of the storage device. The processor 160 can be a central processing unit (CPU), a digital signal processor (DSP), a specific application integrated circuit (ASIC) or any other processor suitable for processing MPEG streams. The data storage 170 can be any storage, which can store MPEG data. For example, the data storage may comprise a random access memory (RAM), a flash memory, a magnetic storage medium (for example, a hard disk drive), an optical storage medium, a magneto storage medium, and optical or any other appropriate data storage.

During operation, the tuner 115 can be tuned to select the current 120 MPEG. In a first reproduction mode, the tuner 115 can propagate the MPEG current 120 to the MPEG decoder 125, which then decodes the MPEG current and sends the current to the display 190. In this playback mode, the MPEG decoder 125 decodes the MPEG current 120. at a speed similar to normal playback speed. With the use of the storage device 150, several additional reproduction trick modes can be implemented by the MPEG receiver 110. For example, the storage device can be used to implement trick mode playback and time shifting. In this arrangement, the MPEG stream 120 can communicate from the tuner 115, through the communication ports 135, 155 to the processor 160, to the recording / playback interface 165 and finally, to the data storage 170. (The decision to send the current 120 MPEG to the storage device, better than to the MPEG decoder 125 depends on the command of the user received at the user's input 140). The processor 160 associates an identifier with each frame within the current 120 MPEG. These frame identifiers can be inserted into the 120 MPEG stream before the 120 MPEG stream is stored in the frame store 170. The frame identifiers can be a sequence of integers or any other type of appropriate identifiers to identify the frames. During playback of the trick mode, the processor 160 typically instructs the recording / playback interface 165 to recover the MPEG stream 120 from the data store 170. The processor 160 may then modify the MPEG stream to cause the MPEG decoder 125 to reproduce the MPEG stream in accordance with a desired trick mode. With reference to Figures 2A and 2B, an example of modifications to the MPEG stream that can be implemented to achieve an advanced trick mode is shown. In the example, the modified MPEG current 250, shown in Figure 2B, is derived from an original 200 MPEG stream, shown in Figure 2A. To achieve a forward reproduction, a number of frames 210 can be removed from the 200 MPEG stream. For example, frames 210-2, 210-3, 210-4, 210-6, 210-7, 210-8 and 210-10 can be removed. The adaptation fields 215 associated with the frames, which were removed, can also be removed. In this way, adaptation fields 215-4 and 215-6 can be removed. Accordingly, frames 210-1, 210-5 and 210-9 and adaptation fields 215-1 and 215-9 are left in the modified 250 MPEG stream, as shown in Figure 2B. The adaptation fields can be added for any frame that does not have an associated adaptation field. Thus, in the present example, the adaptation field 215-5 can be added. The PCR values within the adaptation fields can be adjusted to control the rate at which the synchronization circuit causes the modified 250 MPEG current to be decoded by the MPEG decoder. For example, the PCR value in each adaptation field can be adjusted with an equal substitute PCR to the PTS value contained in the table, with which the adaptation field is associated. Thus, in the example shown, the PCR value in adaptation field 215-1 can be changed from 1000 to 3003, the PCR value in adaptation field 215-5 can be set to 15015, and the PCR value in the adaptation field 215-9 can be changed from 25000 to 27027. The processor can also set a discontinuity_indicator to a value of 1 in each adaptation field before the frame is delivered to the MPEG decoder. The discontinuity_indicator indicates that there has been a discontinuity in the modified MPEG stream. When this occurs, the decoder must load the substitute PCR into the adaptation field within a decoder counter 130, which generates a local system clock synchronizer (LSTC) as described with reference to FIG. 3. With reference to FIG. Figure 3 shows a block diagram of an MPEG synchronization circuit 130. The synchronization circuit 130 is a closed cycle control circuit, which is typical for the synchronization circuits contained in the MPEG decoders. When the MPEG decoder receives a typical unmodified MPEG current, the MPEG decoder loads a first PCR 305 of the MPEG current into a counter 310 synchronized by a voltage controlled oscillator 315. In general, the voltage-controlled oscillator 315 outputs a system clock signal 320 of 27 MHz. A first PCR 305 is used to establish an initial count value, which the counter 310 increases in accordance with the signal 320 of the system clock to generate an LSTC 325. When a next PCR 330 is received, it is compared to the LSTC 325 in a subtractor 335. The subtractor 335 outputs an error signal 340 representing the difference between the LSTC 325 and the value of the next PCR 330. When the value of the LSTC 325 issued exactly matches the next PCR 330, then the error signal 340 will have a value of zero, which indicates that the LSTC 325 is synchronized with a system synchronizer clock (STS) of the encoder. Any difference between the LSTC 325 and the next PCR 330 will cause the error signal 340 to have a non-zero value. The error signal 340 can be filtered by a low pass filter to remove the unwanted harmonics and generate a control voltage 350. The control voltage 350 is then used as a control signal to adjust the frequency of the voltage controlled oscillator 325 and keep the oscillator 325 controlled by voltage secured at the frequency of the system clock synchronizer. For example, when the LSTC 325 has a higher value than the next PCR 330, then the control voltage 350 will cause the frequency of the voltage controlled oscillator 315 to decrease. This may be undesirable for fast forward playback. Since the values of the PCRs 305, 330 are used to synchronize the local system clock synchronizer (LSTC) of the decoder with the synchronizer clock of an encoder system, the modified MPEG stream adaptation fields can be adjusted to effectively disable the frequency adjustment process of the synchronization circuit 130. In particular, by adjusting the indicator discontinuity in each adaptation field causes each substitute PCR to be loaded into the counter 310 as a new PCR 305, and therefore readjusts the LSTC 325 to the new substitute PCR value. Therefore, the subtractor 335 will not receive the next PCR 330 and will not generate an error signal 340. Accordingly, the frequency of the voltage controlled oscillator 315 will not decrease in response to the modified PCR values. In addition, each surrogate PCR value can be loaded into the counter 310 to establish a new LSTC 325 before its associated frame to be delivered to the MPEG decoder. In this way, by the time the frame is delivered to the MPEG decoder, the time represented by the PTS of the frame will have already passed. Accordingly, the MPEG decoder will immediately decode the frame and send the frame to the display, without any added buffer delay. Consequently, the modified MPEG stream will be presented as a fast-forward trick mode. In Figure 4 a flow diagram useful for understanding the present invention is shown. Starting at step 405, the storage device may receive an advance command from the receiver, for example, an advance command entered by the user. The storage device can search the next frame to be delivered based on the forward speed, as shown in step 410. Then, in step 415, the storage device can examine the PTS of the following frame to deliver and create a substitute PCR in the adaptation field and adjust the discontinuity_indicator. To continue, in step 420, the storage device can deliver the adaptation field to the MPEG decoder, which causes the LSTC of the sync circuit of the MPEG decoder to be updated with the new substitute PCR value. In step 425, the storage device can deliver the table correlated with the adaptation field to the MPEG decoder. With reference to decision box 430, step 435, and again to step 410, the process may be repeated until the advance process is stopped. At this point, it should be noted that the foregoing describes the advanced trick mode, the present invention can also be used to implement other trick modes. For example, the PCR values can be adjusted to substitute values that are much lower than the PTS values of the associated frames. Accordingly, the MPEG decoder can be forced to memorize frames for a longer period of time than normal playback. The frames that are displayed can be repeated until the frames in the buffer are decoded and displayed. Also, it should be noted that these and other embodiments of the invention can be contemplated without departing from the basic scope thereof, and the scope is determined by the following claims.

Claims (14)

1. A method for modifying a stream of multimedia content to implement trick mode playback, characterized in that it comprises: setting a discontinuity indicator in an adaptation field associated with a video frame; and adjust a substitute program clock reference value (PCR) in the adaptation field to facilitate the reproduction of the multimedia stream in accordance with a desired trick mode.

2. The method according to claim 1, characterized in that it further comprises: inserting an adaptation field associated with at least one video frame with which the adaptation field was not associated. The method according to claim 1, characterized in that the step of adjusting a substitute PCR value comprises adjusting a substitute PCR value to a value approximately equal to the presentation time stamp (PTS) of the video frame with which it is set. associated with the adaptation field. 4. The method according to claim 1, characterized in that it also comprises removing at least one video frame from the multimedia content stream. 5. The method according to claim 4, characterized in that it also comprises removing at least one adaptation field associated with the video frame removed. 6. The method according to claim 1, characterized in that it further comprises delivering the modified stream of multimedia content to an MPEG receiver. The method according to claim 6, characterized in that the MPEG receiver is a receiver of the Advanced Television Systems Committee (ATSC). A system for modifying a stream of multimedia content to implement a trick mode reproduction, characterized in that it comprises: a processor that adjusts a discontinuity indicator in an adaptation field associated with a video frame and adjusts a reference value of Substitute program clock (PCR) in an adaptation field to facilitate the reproduction of the multimedia stream in accordance with the desired trick mode. The system according to claim 8, characterized in that the processor also inserts an adaptation field associated with at least one video frame with which the adaptation field was not associated. The system according to claim 8, characterized in that the processor adjusts a PCR value to a value approximately equal to a presentation time stamp (PTS) of the video frame with which the adaptation field is associated. The system according to claim 8, characterized in that the processor removes at least one video frame from the multimedia content stream. The system according to claim 11, characterized in that the processor removes at least one adaptation field associated with the video frame removed. The system according to claim 8, characterized in that the modified stream of multimedia content is delivered to an MPEG receiver. The system according to claim 13, characterized in that the MPEG receiver is a receiver of the Advanced Television Systems Committee (ATSC).