Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1997-05-20
2001-09-04
Vu, Huy D. (Department: 2664)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S465000, C370S468000, C370S487000, C348S423100, C348S515000
Reexamination Certificate
active
06285689
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for verifying a multiplexing schedule of digital signals which are suitable to scheduling executed when multiplexing the digital signals, and an apparatus for multiplexing digital signals.
2. Description of the Related Art
Today, an image signal and a speech signal are compressed according to the MPEG (Moving Picture Coding Experts Group) standards compressing system. Then, the compressed signals (elementary streams) compose a multiplexed stream. The multiplexed stream is recorded on a recording medium Further, a multiplexed stream recorded on the recording medium is reproduced by a reproducing apparatus so that the multiplexed stream may be separated into the original elementary streams, from each of which the image signal and the speech signal are decoded.
The method for separating the multiplexed stream into elementary streams is regulated according to the ISO (International Organization for Standardization) 13818-1 or 11172-1, for example. This separating method employs an ideal decoder and is termed a STD (System Target Decoder) model.
The time-divisional multiplexed elementary streams are applied to the STD model. The multiplexed stream is applied to the STD model at regular times by decoding a clock reference that is encoded time information (termed SCR: System Clock Reference).
The multiplexed stream applied to the STD model is divided into the elementary streams by a switch
100
as shown in FIG.
1
. Those elementary streams are supplied to the corresponding buffers
101
to
104
.
The rate information encoded in the multiplexed stream (termed MUX_rate) is supplied to the buffers selected by the switch. The input to the buffer not selected by the switch
100
is 0.
The elementary stream is pulled out of the buffer at each access unit that is a decoding unit defined for each elementary stream. At a decoding time of the access unit that is another piece of time information encoded in the stream, the data of the access unit is instantly pulled out of the buffer and then is supplied to the decoders
106
to
109
. This decoding time guarantees the synchronization among the elementary streams.
For example, for the so-called I picture or P picture, the video data decoded by the decoder
106
is output through a reorder buffer
110
, a selected terminal, and a switch
111
. For the so-called B picture, the video data is output through another selected terminal and the switch
111
. The other data such as the audio data and the subtitle data decoded by the decoders
107
to
109
are directly output.
The time-divisional multiplexing scheduling is executed without overflowing or underflowing the buffers
101
to
104
. Further, the proper clock reference is required to be encoded in the multiplexed stream.
As shown in
FIGS. 2A and 2B
, the multiplexed stream is composed of packets, each packet containing the data of the single elementary stream. The set of the packets composes a pack. The size of the packet or the pack is optional and is ordinarily determined according to a transmission/storage medium.
The pack header contains the SCR that is the reference time of the STD and the MUX_rate encoded therein as additional information. The input rate to the STD model may be variable for each pack according to the MUX_rate encoded on the pack header. Further, the packet header contains time points when the following access units are decoded (termed a DTS Decoding Time stamp) encoded therein. The STD model is executed to reset an internal clock (termed an STC: System Time Clock) to the SCR when the SCR is input to the model. The SCR is required to be inserted to the STD model at intervals of 0.7 sec or shorter.
As shown in
FIG. 2C
, assume that the input of the multiplexed stream to the STD model is executed at the MUX_rate. When the STD model reads the SCR
1
as a value of the SCR inside of the pack header, the STD model serves to set the STC to a value of the SCR
1
. When the STC is counted up to the same value of the SCR
1
, the STD model starts to read the data ES
1
to the buffer
101
and continues to read the data ES
1
until all data is read out of the packet. When the STD model reads the DTS
1
as a value of the DTS, as shown in
FIG. 2D
, the data of the access units stored in the buffer
101
is pulled out at a time point indicated by the DTS
1
.
On the other hand, the buffer
102
is served to read the data ES
2
when the STC value is counted up to the value of the SCR
2
, for example. When the STD model reads the DTS
2
, as shown in
FIG. 2E
, at the time point indicated by the DTS
2
, the data of the access units stored in the buffer
102
is pulled out.
At this time, the amount of the data occupying each buffer is equal to or smaller than a buffer size and the data of the access units decoded at the decoding time point have been already applied in the buffer. Hence, the multiplexing schedule is considered proper.
However, if the amount of data occupying the buffer is too larger or too small, the buffer may be broken.
For example, and with reference to
FIGS. 3A-3E
(wherein
FIGS. 3A-3C
are substantially identical to
FIGS. 2A-2C
and, in the interest of brevity, are not described again), if the amount of data occupying the buffer exceeds a given buffer size, the overflow takes place in the buffer. As shown in
FIG. 3D
, the buffer
101
is overflown while the packet (n, 1) is being input. The schedule in which the packet (n, 1) multiplexes the data ES
1
does not satisfy the STD model.
On the other hand, as shown in
FIG. 3E
, for the data ES
2
, the data of the access units decoded at the decoding time points are not still completely applied to the buffer. This is an underflow of the buffer
102
. The schedule in which the packet (n, 2) multiplexes the data ES
2
is considered erroneous.
As mentioned above, in a case of executing the multiplexing schedule, it is essential to verify whether or not the multiplexed stream generated as a result of the schedule meets the STD model.
In order to verify whether or not the multiplexed stream meets the STD model, it is necessary to grasp the size and the decoding time point of the access unit and simulate the I/O operation of the buffer.
For the ISOs 13818-1 and 11172-1, the conditions the multiplexed stream meets are as follows.
The data does not stay within the buffer for one second or longer (one-second rule).
Less than 31 access units are allowed to be put in the buffer.
The verification is executed at each slit and the DTS (decoding time point).
The slit between the access units is identified by the start code for indicating the start of the start unit. For example, the access unit of the image signal encoded by the ISOs 13818-2 and 11172-2 is started at a four-byte start code.
For the method for detecting a slit between the access units from the data input to the buffer, there has been proposed a method for decoding the compressed data and detecting an end of the access unit and a method for detecting a start code of the access unit in the input data.
By the way, both of these methods are required to check for all data to be input to the buffer and consume long time. Further, the method for actually decoding all data needs an additional processing cost because the decoding is required.
On the other hand, in the method for detecting the start code, as shown in
FIG. 4A
, at the outset, the start codes are located serially on the elementary stream. As to the data divided into packets according to the multiplexing schedule, as shown in
FIG. 4B
, the access unit may be divided into one or more packets. Then, the stream time-divisionally multiplexed with the data of another elementary stream based on the multiplexing schedule is arranged so that the divided access units are multiplexed at remote locations as shown in FIG.
4
C.
Concretely, as shown in
FIG. 4C
, it is impossible to know an end All of the previous access unit until a All time point when the start code is detected. Hence, it is necessary to ver
Negishi Shinji
Oishi Noriaki
Tahara Katsumi
Yasuda Mikita
Frommer William S.
Frommer & Lawrence & Haug LLP
Phan M.
Simon Darren M.
Sony Corporation
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