Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2001-02-27
2003-11-25
Diep, Nhon (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C348S699000
Reexamination Certificate
active
06654421
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus, a method and a computer program product for transcoding a coded multiplexed sound and moving picture sequence, and more particularly, to an apparatus, a method and a computer program product for demultiplexing the first coded multiplexed sound and moving picture sequence signal containing video information, audio information, and program information into video information data strings, audio information data strings, and control information data strings, compress the video information data strings, and multiplex the compressed video information data strings, the audio information data strings, and the control information data strings in to the second coded multiplexed sound and moving picture sequence signal, and thus converting a first coded multiplexed sound and moving picture sequence signal containing video information, the audio information, and the program information in the form of bit streams transmitted at a first bit rate into a second coded multiplexed sound and moving picture sequence signal in the form of bit streams transmitted at a second bit rate lower than the first bit rate.
2. Description of the Related Art
There have so far been proposed a wide variety of systems for compressing and encoding a moving picture having a considerable large amount of 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”. The MPEG-2 system is designed to encode a digital video signal associated with a digital audio signal to generate a coded multiplexed sound and moving picture sequence signal in the form of bit streams. For avoiding tedious repetition in the following description, the bit streams conformable to the above MPEG-2 standard will be referred to as “MPEG-2 bit streams”, and a device for encoding a digital video signal associated with a digital audio signal to generate a coded multiplexed sound and moving picture sequence signal in the form of bit streams will be referred to as an “encoder”, hereinlater. In recent years, the MPEG-2 standard has become increasingly applied for various technical systems such as a communicating system, and a television broadcasting system.
The above MPEG-2 bit streams are each of a hierarchical structure consisting of: a top, sequence layer; a GROUP OF PICTURES layer; a picture layer; a slice layer; a macroblock layer; and a low, block layer.
The typical encoder is operable under the MPEG-2 standard through a method of compressing and encoding a moving picture as follows. The method comprises the steps of:
(a) inputting the moving picture sequence consisting of a series of pictures;
(b) temporally storing the series of 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 a 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 decode the coded signal through a 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 pictures of the other types, so that a single I-picture can be reproduced as a static image only by itself. A P-picture can be predicted on the basis of the I-picture or a P-picture located on a position prior to the P-picture to be encoded.
In the above encoder, a volume of information on the coded moving picture sequence signal is, however, variable. In particularly, the volume of information increases remarkably when a scene is changed. 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 are transmitted from the encoder to the decoder, the input buffer overflows with the bits of the coded moving picture sequence signal thereby making the decoder difficult to process the coded moving picture sequence signal. In order to transmit such coded moving picture sequence signal having a variable number of bits through the transmitting path at a predetermined bit rate and to make it possible for any decoder to receive the whole of the coded moving picture sequence signal without overflow, the encoder comprises: an output buffer for temporally storing the coded moving picture sequence signal before transmitting the coded moving picture sequence signal through 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 to be transmitted to the decoder from exceeding the volume of the input buffer of the decoder 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”. The rate controlling method according to the TM-5 comprises the steps of:
(I) allocating a target number of bits to a picture of each type on the basis of the total number of bits available to the current pictures to be encoded in the GROUP OF PICTURES, i.e., R, which will be described hereinafter;
(II) computing the reference value of a quantization parameter used for the quantization of each of macroblocks in a current picture on the basis of the utilization volume of a “virtual buffer” to perform the rate control; and
(III) modulating the reference value of the quantization parameter in accordance with the spatial activity in the macroblock.
Furthermore, there are many types of decoders. For instance, a decoder is designed to decode the coded signal in a unique compression format different from that of MPEG-2 bit streams, and another decoder is connectable to a transmitting path having a different bit rate. The decoders of these types are therefore required to provide with an apparatus, a so-called transcoder, for converting the MPEG-2 bit streams into another appropriate coded signal in the specified format having the required bit rate. The transcoder makes it possible for the encoder to transmit the coded signal to any types of decoders.
Referring to
FIG. 18
of the drawings, there is shown a conventional transcoder of one typical type as a first conventional transcoder
50
. The conventional transcoder
50
has an input terminal a, 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
Hanamura Tsuyoshi
Kasai Hiroyuki
Nishimura Satoshi
Ozaki Seiji
Tominaga Hideyoshi
Albrecht Ralph P.
Diep Nhon
Tominaga Hideyoshi
Venable LLP
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