Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-02-14
2003-04-29
Diep, Nhon (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06556626
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to MPEG (Moving Picture Experts Group) decoding technology and more particularly to an MPEG decoder, MPEG system decoder and MPEG video decoder which are capable of decreasing the number of circuits required for processing of PTS (Presentation Time Stamp) / DTS (Decoding Time Stamp) values.
2. Description of the Related Art
In an MPEG system, time division multiplexing of an MPEG video stream obtained by encoding image data and an MPEG audio stream obtained by encoding audio data is performed by a sender to form an MPEG system stream for transmission and each of the MPEG video streams and the MPEG audio streams is decoded by a receiver separately to reproduce its original image data and its original audio data. At this point, since the image data and audio data are transmitted in a compressed state, the sender transmits time information about its original data at the same time and then the receiver reconstructs time information of the original data using the above time information and standard time transmitted by the sender to decode and reproduce the image and audio data for outputting.
FIGS. 5A
,
5
B and
5
C are diagrams showing structures of such MPEG data. The MPEG data is hierarchially structured. A top hierarchy is composed of a system layer. A PES (Packetized Elementary Stream) packet obtained by packetizing video data and a PES packet obtained by packetizing audio data being mixed constitutes the system stream as shown in FIG.
5
A. Also, as shown in
FIG. 5A
, the PES packet is composed of a system header and packet data obtained by packetizing video or audio data. The system header is comprised of 4-byte codes including a head starting code having a fixed value (24 bits), a 8-bit start code ID showing a type of data and PTS/DTS values being time information.
The PTS (Presentation Time Stamp) is information used to manage time for outputting the reproduced MPEG image, while the DTS (Decoding Time Stamp) is information used to manage time for starting to decode image data. The MPEG decoder, after adjusting time for reproducing and decoding image by comparing an STC (System Time Clock) value, which is reference time in the MPEG decoder, with the PTS/DTS values, is adapted to perform AV (Audio Visual) synchronization adjustment so as to synchronize image reproducing output to voice reproducing output. The PTS/DTS values are inserted singly or together at an interval of a relatively long time when necessary. Moreover, the PTS/DTS values are inserted both in the case of an MPEG
1
system in which a picture is corresponded to a frame of a reproduced image and in the case of an MPEG
2
-PS system in which the picture is corresponded to the frame or field of the reproduced image.
In the MPEG decoder, each of a video ES (Elementary Stream) and an audio ES is separated from the system layer for processing. The video: ES is formed with video packet data strings in the system stream as shown in
FIG. 5B. A
plurality of the packet data in the video ES constitutes one picture and picture data contains a plurality of pictures as shown in FIG.
5
C. For example, a picture
1
is composed of packet data
1
, packet data
2
, . . . , N−1, and a picture
2
is composed of packet data N, N+1, . . . . The picture data contains a head starting code composed of a fixed value (24 bits) and 8bit start code ID showing a type of data.
According to specifications of the MPEG system, “00 to B8” (in hexadecimal) are used as a start code ID of data in each layer described above to be inserted in the video ES and “BA to FF” (in hexadecimal) are used as the start code ID of data in each layer to be inserted in the system stream.
FIG. 6
is a schematic block diagram showing configurations of the conventional MPEG decoder. Operations of the conventional MPEG decoder are hereafter described.
A system decoder
1
, when receiving a system stream, decodes a system layer, detects PTS/DTS values and then stores them into a PTS/DTS register
1
1
.
The system decoder
1
is used to output a video stream obtained by decoding the system stream and by separating it. If the video stream is data with the PTS/DTS values added, the system decoder
1
outputs a DTS flag. A memory controller
2
is adapted to store the video stream fed by the system decoder
1
into a memory
3
and, if the existence of a PTS flag is detected, holds an address of data with the PTS added in a PTS/DTS data address register
2
1
.
The memory controller
2
, when a video decoder
4
becomes processable, reads the video stream from the memory
3
and outputs it to the video decoder
4
and, if the video stream is data with PTS/DTS values added, outputs the PTS flag to the video decoder
4
.
The video decoder
4
is adapted to decode the inputted video stream. At this point, if the existence of the PTS flag is detected, the video decoder
4
informs a CPU (Central Processing Unit)
5
that it has read data with the PTS/DTS values added, by outputting the PTS flag to the CPU
5
. The CPU
5
, when receiving the PTS flag, checks the address register
2
1
storing data with the PTS/DTS values added and, at the same time, outputs an instruction to clear the PTS/DTS values held by the PTS/DTS register
1
1
to the system decoder
1
.
The CPU
5
in the MPEG decoder, by comparing an STC value, which is reference time information fed by an STC section
6
, with the PTS/DTS values stored in the PTS/DTS register
1
1
, generates an image reproducing output based on decoded video data in accordance with the reference time. For example, if there is a delay or an advance in outputting a reproduced voice and in outputting a reproduced image, the AV (Audio-Visual) synchronization processing is performed by a method employing a deletion (or a skipping process) for every picture or a repetition (i.e., a repeating process) of outputting or by a similar method to synchronize the separately decoded voice reproducing output to the image reproducing output.
In the conventional MPEG decoder as shown in
FIG. 6
, during a period while the system decoder
1
is performing processing of the PTS/DTS values stored in the PTS/DTS register
1
1
, if newly inputted video stream is data with the PTS/DTS values added, it cannot be processed and must be discarded accordingly. It is impossible to completely process all of the PTS/DTS values, making it difficult to perform the AV synchronization satisfactorily.
In Japanese Laid-open Patent Application No. Hei8-212701, a method is disclosed in which a plurality of PTS values separated from a video stream is sequentially accumulated in a register as a combination with an address and, when the video stream is supplied to a decoding section, the fact is detected, by comparing an address of the video stream with an address read from the registers that the data is one with the PTS value added and by associating the PTS value with a picture, decoding is performed by the skipping or repeating processing.
Moreover, in Japanese Laid-open Patent Application No. Hei10-98699, a method is disclosed in which, by inserting PTS data into an arbitrary detectable position within a data stream such as a video ES or the like and by transferring it to a decoder, fact is detected by a decoder that data is one with the PTS value added.
As described above, the conventional MPEG decoder as shown in
FIG. 6
has a problem in that the MPEG decoder, when receiving the input system stream, cannot carry out the processing of the PTS/DTS values if data with the PTS/DTS values added is consecutively contained in the system stream
On the other hand, according to the method disclosed in the above Japanese Laid-open Patent Application No. Hei8-212701, though the processing can be performed with all the PTS data stacked, when the decoding is. performed, the processing must be done after confirming a conformity detected by comparing an address of the PTS value read from the register with an address of the video stream, thus causing the structure of required circuits
Diep Nhon
Hayes & Soloway PC
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