Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-06-28
2003-07-01
Philippe, Gims S. (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240020, C382S298000, C348S404100
Reexamination Certificate
active
06587508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus, method and computer program product for transcoding a coded moving picture sequence, and more particularly, to an apparatus, method and computer program product for converting a first coded moving picture sequence signal in the form of bit streams transmitted at a first bit rate into a second coded moving picture sequence signal in the form of bit streams transmitted at a second bit rate lower than the first bit rate by adapting a quantization parameter to perform the effective real timely rate control over the second coded moving picture sequence signal with low delay.
2. Description of the Related Art
There has so far been proposed a wide variety of systems for compressing and encoding a moving picture having a considerable large data to produce a coded moving picture sequence signal. The international standard, ISO-IEC 13818-2, was created for a system operable to encode a digital video signal associated with a digital audio signal and commonly called “Moving Picture Expert Group Phase 2”, i.e., “MPEG-2”. In such encoding system, the coded moving picture sequence signal is outputted in the form of bit streams. In particular, the bit streams conformable to above MPEG-2 standard will be referred to as “MPEG-2 bit streams” hereinlater. Recently, the system of this type becomes more utilizable for various technical fields, such as a communicating system, a television broadcasting system, and so on.
The above MPEG-2 bit streams have a hierarchical structure consisting of: in turn, a top, sequence layer, a GROUP OF PICTURES layer, a picture layer; a slice layer; a macroblock layer; and a low, block layer.
According to the MPEG-2 standard, a typical encoder is operable to employ the following method of compressing and encoding a moving picture. The method comprises the steps of:
(a) inputting the moving picture sequence consisting of a series of pictures;
(b) temporally storing the pictures as frames in memories, respectively;
(c) computing a difference between one frame and another frame to eliminate redundancy in a time axis direction; and
(d) orthogonal transforming, e.g., discrete cosine transforming (DCT), a plurality of picture elements within each of the frames to eliminate redundancy in a spatial axis direction.
The encoder thus constructed can compress and encode the moving picture to generate and output the coded moving picture sequence signal in the form of the MPEG-2 bit streams through a transmitting path at a predetermined bit rate. The coded signal is then transmitted from the encoder to a decoder which is adapted to decode the coded signal to reproduce the moving picture. The typical decoder is operated to employ so-called bi-directionally predicting method which comprises the steps of:
(a) storing one reproduced picture, generally referred to as “intra-picture”, i.e., “I-picture”, in a first frame memory;
(b) estimating another picture generally referred to as “predictive-picture”, i.e., “P-picture”, followed by the I-picture, on the basis of the information on a difference between I-picture and P-picture;
(c) storing the estimated picture in a second frame memory; and
(d) estimating further another picture interposed between the I-picture and P-picture, generally referred to as “bi-directionally predictive-picture”, i.e., “B-picture”.
Here, the I-picture is encoded independently of the other types of pictures, so that the I-picture can be reproduced as a static image only by itself. The P-picture can be predicted on the basis of the I-picture or P-picture located on a position prior to this P-picture to be encoded.
In the above encoder, the volume of information on the coded moving picture sequence signal is, however, variable, in particularly, remarkably increased in accordance with a change of scene. The decoder is generally provided with an input buffer for receiving the coded moving picture sequence signal from the encoder. The input buffer of the decoder, however, has a limited storage capacity. Therefore, when a large number of bits of the coded moving picture sequence signal is transmitted from the encoder to the decoder, the input buffer overflows with the large number of bits of the coded moving picture sequence signal thereby making the decoder hard to process the coded moving picture sequence signal. In order to transmit such coded moving picture sequence signal having a variable volume of information on the transmitting path at a predetermined invariable bit rate and to enable any decoders to receive the coded moving picture sequence signal, the encoder comprises: an output buffer for temporally storing the coded moving picture sequence signal before transmitting the coded moving picture sequence signal on the transmitting path; and a rate controller for controlling the volume of information on the coded moving picture sequence signal stored in the output buffer so as to keep the volume of information on the coded moving picture sequence signal from exceeding the volume of the buffer and then to control the bit rate of the coded moving picture sequence signal.
A typical rate controlling method in MPEG-2 standard is described in “ISO-IEC/JTC1/SC29/WG11/N0400 Test Model 5”, April, 1993, hereinlater referred to as “TM-5”. According to the TM-5, the rate controlling method comprises the steps of:
(I) allocating a target bit by estimating the number of bits available to code the next picture before coding the current picture;
(II) computing the reference value of the quantization parameter used for the quantization of each of macroblocks in the current pictures by means of a “virtual buffer” to perform the rate control; and
(III) modulating the reference quantization parameter in accordance with the spatial activity in the macroblock.
Furthermore, there are many types of decoders, for instance, one is designed to decode the coded signal having a specific format different from that of MPEG-2 bit streams, and another is connectable to a transmitting path having a different bit rate. These types of decoders are therefore required to provide with an apparatus, so-called transcoder, for converting a bit rate of the MPEG-2 bit streams into another appropriate coded moving picture sequence signal. The coded moving picture sequence signal can be transmitted to any types of decoders from the encoder via an appropriate transcoder.
Referring to
FIG. 13
of the drawings, there is shown one typical type of the conventional transcoders as a first conventional transcoder
50
. The conventional transcoder
50
has an input terminal a
1
electrically connected to a first transmitting path, not shown, and an output terminal a
2
electrically connected to a second transmitting path, not shown. The conventional transcoder
50
is designed to input first bit streams b
1
at a predetermined input bit rate through the input terminal a
1
, to convert the first bit streams b
1
into second bit streams b
2
to be output at a predetermined output bit rate, i.e., a target bit rate, lower than the input bit rate of the inputted first bit streams b
1
, and to then output the second bit streams b
2
through the output terminal a
2
. The conventional transcoder
50
comprises a variable length decoder
51
, referred to as “VLD” in the drawings, a de-quantizer
53
, referred to as “IQ” in the drawings, a quantizer
55
, referred to as “Q” in the drawings, a variable length encoder
57
, referred to as “VLC” in the drawings, and a rate controller
59
.
The variable length decoder
51
is electrically connected to the input terminal a
1
and designed to decode a coded moving picture sequence signal within the first bit streams b
1
inputted through the input terminal a
1
to reconstruct an original picture data for each of pictures including a matrix of original quantization coefficients, referred to as “level”, for each of macroblocks within each of the pictures and an original quantization parameter, hereinlater referred to as “first quantization parameter Q
1
”.
The de-quantizer
53
is
Hanamura Tsuyoshi
Kasai Hiroyuki
Nishimura Satoshi
Tominaga Hideyoshi
Aitken Richard L.
Media Glue Corporation
Philippe Gims S.
Venable
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