Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-09-20
2004-06-22
Kelley, Christopher (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240000, C375S240010
Reexamination Certificate
active
06754276
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a system stream creating apparatus for creating a system stream from a video stream and an audio stream which have been generated in accordance with the MPEG standard. More particularly, the present invention relates to a system stream creating apparatus for creating a system stream which easily conforms to the MPEG standard and the DVD standard and to a DVD recorder having the system stream creating apparatus.
(2) Description of Related Art
Recently, DVD-RAM, a phase-change type optical disc having a capacity of several giga bytes, has come on the market. It is expected that the DVD-RAM will be used as a recording/reproducing medium not only for computers but for other commercial products. This expectation has been enhanced as MPEG (MPEG2), a standard for encoding the digital audiovisual (hereinafter referred to as AV) data, has become commercially practical.
MPEG
The AV data recorded on the DVD-RAM conforms to an international standard called MPEG (ISO/IEC13818). The capacity of the DVD-RAM, though several gigabytes, is not enough to record uncompressed digital AV data. The AV data is therefore recorded after it is compressed. The MPEG standard is prevalent as a method for compressing AV data. Thanks to the recent progress in the LSI circuit technology, MPEG codec (compression/decompression LSI) has come into practical use. This has made it possible for DVD recorders to compress/decompress digital data in accordance with the MPEG standard.
MPEG has the following two main characteristics for achieving highly efficient data compression.
The first characteristic is that MPEG compresses moving-image data using the time correlation characteristic found between frames as well as the spacial frequency characteristic which has been used conventionally. For data compression in MPEG, each frame (in MPEG, also referred to as Picture) is classified into I-Picture (Intra-Coded Picture), P-Picture (Predictive-Coded Picture which uses the I-Picture and reference to past), and B-Picture (Bidirectionally Predictive-Coded Picture which uses the I-Picture and reference to past and future).
To achieve trick plays such as fast-forward, rewinding, and a reproduction from any desired point when reproducing data stored in a storage medium, MPEG defines GOP (Group Of Pictures). This is because in MPEG, frames do not complete in themselves and as described above, video data is encoded based on prediction using past and future frames. As a result, frames are divided into groups of Pictures, the groups being called GOPs which each include at least one I-Picture. With such a construction, random access is available.
The second characteristic of MPEG is that the amount of coding is assigned dynamically in units of Pictures in proportionate to the complexity of images. In MPEG, the decoder includes an input buffer in which data is stored beforehand. This construction enables complicated images to be assigned a great amount of coding.
The audio data for DVD-RAM is compressed with one method: MPEG audio or Dolby digital (AC-3) for compressing data, or LPCM not for compressing data. The Dolby digital and the LPCM use fixed bit rates. The MPEG audio uses a variable bit rate in which audio frames are generated in fixed synchronization, with different sizes.
The AV data is multiplexed into one stream with the “MPEG system” method.
FIG. 1
shows the construction of the MPEG system. In the drawing, “
21
” represents a pack header, “
22
” a packet header, and “
23
” a payload. The MPEG system has a hierarchical structure including packs and packets. Each packet is composed of a packet header
22
and a payload
23
. The AV data is divided into portions of an appropriate size from the start of the AV data. The payload
23
stores a piece of divided data. The packet header
22
includes a stream ID, DTS (Decoding Time Stamp), and PTS (Presentation Time Stamp) as information of the AV data stored in the payload
23
. The stream ID is used to identify the AV data stored in the payload
23
. The DTS indicates a time when the AV data stored in the payload
23
is decoded and is represented with accuracy of 90 kHz. It should be noted here that the packet header
22
does not include DTS when, for example, audio data is decoded and presented at the same time. The pack is a unit including a plurality of packets. In DVD-RAM, one packet is used as one pack. Therefore, each pack is composed of a pack header
21
and a packet (composed of a packet header
22
and a payload
23
). In the pack header, SCR (System Clock Reference) is recorded. The SCR indicates a time when the AV data stored in the pack is input into the decoder buffer, with accuracy of 27 MHz. For DVD-RAM, the types of the packets are determined in accordance with the type of the stream the DVD-RAM stores. The packet types are, for example, the video stream packet for storing MPEG video data, the audio stream packet for storing MPEG audio data, the private stream
2
packet for storing Dolby AC-3 audio data, and the padding stream packet for storing dummy data which is discarded by the demultiplexer during decoding.
The DVD-ROM records such an MPEG system stream so that one pack has one sector (=2,048 bytes).
Now, the decoder for decoding the above MPEG system stream will be described.
FIG. 2
shows a decoder model (P-STD) for the MPEG system decoder. The decoder includes STC (System Time Clock)
31
which clocks the standard time in the decoder, a demultiplexer
32
which decodes and demultiplexes the system stream, a video buffer
33
for a video decoder, the video decoder
34
, a re-order buffer
35
which temporarily stores the I- and P-Pictures for the purpose of rearranging the I-, P-, and B-Pictures for presentation, a switch
36
which adjusts the output order of the I-, P-, and B-Pictures stored in the reorder buffer, an audio buffer
37
for an audio decoder, and the audio decoder
38
.
The MPEG system decoder with the above construction processes the MPEG system stream as follows. When the time of the STC
31
matches the SCR written in the pack header in a pack, the demultiplexer
32
inputs the pack. The demultiplexer
32
decodes the stream ID of the packet header, and transfers the data in the payload to the decode buffer corresponding to the stream. The demultiplexer
32
also extracts the PTS and. DTS from the packet header. The video decoder
34
extracts Picture data from the video buffer
33
when the time of the STC
31
matches the DTS, decodes the Picture data, stores the I- and P- Pictures in the re-order buffer
35
, and outputs the B-Pictures for presentation. The switch
36
is positioned on the side of the re-order buffer
35
when the video decoder
34
decodes an I- or P-Picture, and on the side of the video decoder
34
when the video decoder
34
decodes a B-Picture. The audio decoder
38
extracts data of one audio frame from the audio buffer
37
when the time of the STC
31
matches the PTS (for audio data, there is no DTS) and decodes the extracted data.
For MPEG, “0x00” (in this document, “0x” indicates that the succeeding numerals represent a hexadecimal value) has special meaning. Every meaningful group of data in MPEG begins with a 4-byte identification code. For example, the pack header begins with a 4-byte code, “0x000001BA”, the GOP “0x000001B8”, and the Picture “0x00000100”. “0x00” is referred to as “next start code” since a sequence of two “next start codes” and one “0x01” indicates the start of a meaningful group of data. In MPEG, there is no limit to the number of successive “next start codes”, but when “0x01” is found, the position two next start codes before the “0x01” is recognized as the start of the meaningful group of data. The “next start codes” before these codes are skipped by the decoder during reproduction.
Now, a method of multiplexing data into the MPEG system stream will be described with reference to
FIGS. 3A
to
3
D.
FIG. 3A
shows a video frame. FIG
3
B shows a video buffer.
FIG. 3C
shows an MPEG
Harumoto Hideaki
Kawasaki Kojiro
Okada Tomoyuki
Kelley Christopher
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
Wong Allen
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