Multiplex communications – Communication techniques for information carried in plural... – Transmission bandwidth conservation
Reexamination Certificate
1997-10-28
2001-02-13
Vincent, David R. (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Transmission bandwidth conservation
C370S468000, C375S240020
Reexamination Certificate
active
06188700
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an encoded signal transmission method and apparatus suitable for encoding a digital signal at a variable bit rate on a transmission side and transmitting the encoded signal at the variable bit rate to a receiving side.
2. Description of the Related Art
In order to realize transmission of moving picture signals with high quality as the next-generation television broadcasting, a project of digitizing moving picture signals has been under way. In this case, since directly digitizing moving picture signals generates a huge amount of data, encoding of data (i.e., information compression) is required for efficient transmission of the data on a limited transmission line.
Meanwhile, in general, moving pictures are not stationary and the pattern and movement on a screen vary temporally. In some cases, the pattern and movement greatly differ between the center and peripheral portions of a picture within the screen. Therefore, the amount of generated information in encoding by an encoder varies, depending on such nature of the picture. To send such information at a constant transmission bit rate, a transmission buffer is prepared at the final stage of an encoder system. That is, an encoded output with the varying amount of generated information is temporarily stored in the transmission buffer and is read out and outputted to a transmission line at a predetermined transmission bit rate.
FIG. 1
is a block circuit diagram showing a conventional encoder with a constant output bit rate (hereinafter referred to as encoder system). In this encoder system shown in
FIG. 1
, a transmission buffer (hereinafter referred to as encoder buffer)
13
is provided between a video encoder
12
supplied with a video input via a terminal
11
, and a transmission line. Thus, control is performed so as to smooth fluctuations in the amount of generated bits in a short period of time from the video encoder
12
and to output a bit stream from the encoder buffer
13
at a constant bit rate.
Information including the amount of generated bits S
21
of the encoded picture from the video encoder
12
, a bit rate R from a terminal
16
and a decoder buffer size B from a terminal
10
is inputted to a rate controller
15
. On the basis of a video buffering verifier (VBV) model as later described, the rate controller
15
calculates the amount of allocated bits S
22
of a picture to be encoded next, without causing overflow or underflow of a decoder buffer of the size B provided on the side of a decoder system. The rate controller
15
then sends and designates the information of the amount of allocated bits S
22
to the video encoder
12
.
The encoder buffer
13
supplied with the video bit stream from the video encoder
12
has a code buffer of a size equal to at least the decoder buffer size B. The code buffer is generally included in the transmission buffer.
The bit stream outputted from the encoder buffer
13
is inputted to a multiplexer
14
. Although not shown, an encoded bit stream of an audio signal is also inputted to the multiplexer
14
. The multiplexer
14
performs system encoding and multiplexing of a plurality of input bit streams, and outputs multiplexed streams from a terminal
17
.
The start of output of the bit stream from the encoder buffer is indicated by a start controller
19
. In the configuration shown in
FIG. 1
, a switch
20
provided on the output side of the encoder buffer
13
is controlled by the start controller
19
. The start time is calculated from information including the bit rate R and the bit occupancy quantity b
0
at the start of decoding of the decoder buffer from a terminal
18
, as later described.
FIG. 2
is a block diagram showing a conventional decoder (hereinafter referred to as decoder system). A multiplexed stream from a terminal
25
is inputted to a demultiplexer
26
, and the video bit stream split by the demultiplexer
26
is stored in a receiving buffer (hereinafter referred to as decoder buffer)
27
. The decoder buffer
27
is adapted for absorbing fluctuations in the amount of bits read out in a short period of time by a video decoder
28
. The decoder system is passive to the bit stream transmitted thereto. Therefore, in order to enable the video decoder
28
to perform stable video reproduction, the encoder system must encode data carefully enough to prevent overflow or underflow of the decoder buffer
27
.
As a moving picture encoding method, the Moving Picture Experts Group (MPEG) standards have been known. The MPEG is an abbreviation of the group for examining moving picture coding for storage, of the International Organization for Standardization/International Electrotechnical Commission, Joint Technical Committee 1/Sub Committee 29 (ISO/IEC JTC1/SC29). The standards include ISO11172 as the MPEG1 standard and ISO13818 as the MPEG2 standard. In these international standards, ISO11172-1 and ISO13818-1 are provided as standards for multimedia multiplexing, ISO11172-2 and ISO13818-2 as video standards, and ISO11172-3 and ISO13818-3 as audio standards.
The MPEG standards prescribe an ideal input/output model of the decoder buffer
27
of the decoder system, and prescribes that on the assumption of the model of the decoder buffer (i.e., the ideal model of the decoder buffer), the encoder system should encode data carefully enough to prevent overflow or underflow of the decoder buffer
27
. The input/output model of the decoder buffer
27
of the decoder system is described in the ISO/IEC 11172-2 Annex C or ISO/IEC 13818-2 Annex C, as a video buffering verifier (VBV) model. A buffer of the VBV model is referred to as a VBV buffer.
The VBV buffer size of the decoder system is indicated by an identifier “vbv_buffer_size” in the MPEG bit stream. The standard size is 1.75 Mbits, for example, in a main profile at main level (MP@ML).
The VBV of the decoder system is assumed to operate under the following ideal conditions.
(1) The bit stream for each picture is outputted instantaneously from the decoder buffer, and each picture is decoded instantaneously.
Under these conditions, when the bit stream is transmitted from the encoder system to the decoder system on the real-time basis, the transmission buffer (encoder buffer) of the encoder system must operate under the following ideal conditions.
(
2
) Each picture is encoded instantaneously, and the bit stream for each picture is inputted instantaneously to the encoder buffer.
The VBV model in the case where the encoder system and the decoder system operate on the real-time basis via a transmission line as in broadcast or communication will now be described. In the encoder system, as shown in
FIG. 1
, the bit stream is outputted from the encoder buffer
13
at a constant bit rate. Therefore, the bit stream is inputted to the decoder buffer
27
shown in
FIG. 2
at a constant bit rate.
FIG. 3
shows an example of changes in the bit occupancy quantity of the buffers of the encoder system and the decoder system in conformity with the VBV model. In
FIG. 3
, the area on the right side of a line c-d shows changes in the bit occupancy quantity of the decoder buffer, and the area on the left side of the line c-d shows changes in the bit occupancy quantity of the encoder buffer.
The horizontal axis t expresses the lapse of time. In this case, two time bases are drawn, with an upper time base expressing the lapse of time on the side of the encoder system and a lower time base expressing the lapse of time on the side of the decoder system. In
FIG. 3
, the line c-d is shared by the encoder system and the decoder system for simplification, and there is no time difference between the encoder system and the decoder system. Actually, however, a constant transmission line delay time D
0
exists between the encoder system and the decoder system. Therefore, the time of a point c is the origin t=0 on the time base of the encoder system while it is t=D
0
on the time base of the decoder system. The time D
0
includes the processing ti
Kato Motoki
Koyanagi Hideki
Limbach & Limbach L.L.P.
Sony Corporation
Vincent David R.
LandOfFree
Method and apparatus for encoding MPEG signals using... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for encoding MPEG signals using..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for encoding MPEG signals using... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2575190