Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
2000-09-20
2004-10-05
Chevalier, Robert (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000, C386S349000
Reexamination Certificate
active
06801707
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an encoding/recording device and an encoding/recording method for compressing and encoding video data based on time correlation properties of the video data, multiplexing the video data with audio data, and recording the multiplexed video data and audio data. More specifically, the present invention relates to a technology for enhancing a function to suspend recording by the encoding/recording device.
(2) Description of the Prior Art
In recent years, increasing amount of information is digitized. Especially, more and more sound and images are digitized since digital information suffers no degradation with the passage of time and is relatively easy to be processed. Hereafter, sound and images in digital format is collectively called “AV (audio-video) data”.
MPEG (Moving Picture Expert Group, including MPEG-2 in this specification) is an international standard used to compress AV data to record it effectively.
MPEG for video data uses a compression method based on time correlation properties between different pictures in addition to a conventionally used compression method based on discrete cosine transform (DCT). The compression method based on the time correlation properties achieves a high compression rate by representing one picture as differential data between the picture and other similar pictures to this picture which are reproduced before and after this picture. However, with this MPEG based on the time correlation properties, presenting order and decoding order for pictures are different, and therefore it is necessary to record, or decode and store a picture that is referred to for encoding another picture, prior to the other picture that refers to this picture. For MPEG, a picture that is referred to for encoding of another picture is called an I picture (intraframe predictively encoded picture) or a P picture (interframe predictively encoded picture). A picture that is encoded referring to another picture (I or P picture) is called a B picture (bi-directionally predictively encoded picture).
Video data is a plurality of sets of still image data per unit time (each set of still image data is hereafter called a video frame), and therefore video data usually contains similar images. As MPEG can provide a higher compression rate for video data containing more images similar to one another, MPEG is suitable for compression of video data.
MPEG can effectively compress data by providing a different compression rate for each image and dynamically assigning encoding bits to the image in accordance with its complexity.
Audio data, on the other hand, has a smaller size than video data, and therefore a different compression method than used for the video data is usually used.
For instance, a DVD recorder that records AV data onto a DVD-RAM according to MPEG allows a user to select whether to compress audio data. When selecting that the AV data should be compressed, the user can further select whether MPEG Audio or Dolby AC3 should be used as a compression method. The DVD recorder then encodes the audio data using the selected compression method. When the user selects that no compression is performed for the audio data, LPCM (linear pulse code modulation) is performed for the audio data. The DVD recorder then encodes and compresses video data according to MPEG, multiplexes the encoded video data and audio data into a piece of MPEG System stream according to MPEG System, and records the piece of MPEG System stream.
With MPEG System, audio data and video data, which have been encoded and compressed, are divided into audio packets and video packets that have predetermined sizes, and time-division multiplexed into MPEG System stream. Hereafter, the terms “audio data” and “video data” are used to represent audio data and video data that have been encoded and compressed. MPEG System stream has a hierarchical structure composed of a pack and a packet, with one pack being composed of one or more packets. For instance, a pack recorded on a DVD-RAM is composed of one packet. For ease of explanation, one pack is assumed to be composed of one packet in this specification, as is the case with a pack recorded on a DVD-RAM.
FIG. 1
shows a construction of a pack and packet generated according to MPEG System.
Each packet is 2KB, and contains a pack header
11
, a packet header
12
, and a payload
13
.
The pack header
11
contains an SCR (system clock reference) that shows a time at which the pack should be inputted to a video buffer or an audio buffer in an MPEG decoder.
The packet header
12
contains the following information: a stream ID that identifies the content of the payload
13
; a DTS (Decoding Time Stamp) showing a decoding start time; and a PTS (Presentation Time Stamp) showing a presentation time. Note that an audio pack does not contain a DTS since audio data is decoded and presented almost simultaneously.
The payload
13
is audio data or video data.
Audio data is usually divided into audio packets that each contain audio data corresponding to one audio frame, and therefore a large-capacity audio buffer is not required by the MPEG decoder. As with video data, however, video frames have different sizes, and the differences in the size between different video frames are very large. For instance, video data corresponding to one video frame may be divided into a plurality of video packets. Accordingly, an MPEG decoder is required to have a video buffer that has at least the same size as a video frame of the largest size. Packs are positioned in MPEG System stream in order of an SCR, the earliest SCR first.
FIG. 2
is a diagram showing a standard decoder for MPEG System stream.
This MPEG decoder comprises the following elements: an STC (system time clock)
21
that generates a system time based on which the MPEG decoder operates; a demultiplexer
22
that separates system stream into audio packets and video packets based on a stream ID of each packet; a video buffer
23
that temporarily buffers video data; a video decoder
24
that decodes video data; a reordering buffer
25
that temporarily stores video data to be referred to by other video data; a switch
26
that is used to adjust output order of video data; an audio buffer
27
that temporarily buffers audio data; and an audio decoder
28
that decodes audio data.
The following describes decoding operations by this MPEG decoder.
A pack is extracted to be inputted to the demultiplexer
22
when a system time generated by the STC
21
agrees with an SCR written in the pack. The demultiplexer
22
then refers to a stream ID of the inputted pack and sends a packet in the pack to either the video buffer
22
or the audio buffer
27
accordingly. The video buffer
23
accumulates payloads of packets sent by the demultiplexer
22
and manages a DTS and a PTS of each packet. The video decoder
24
reads video data that has a DTS equal to a current system time from the video buffer
23
. This read video data corresponds to one video frame. The video decoder
24
then decodes the read video data. Following this, video data (i.e., an I picture or a P picture) which is referred to for encoding of other pictures is temporality buffered by the reordering buffer
25
, and selectively outputted in accordance with a PTS via the switch
26
. The video decoder
24
decodes video data (i.e., B picture) that is encoded referring to other pictures, and outputs it immediately. On receiving audio data that is a payload of each audio packet from the demultiplexer
22
, the audio buffer
27
buffers it and manages a PTS in the audio packet. The audio decoder
28
reads audio data that has a PTS equal to a current system time from the audio buffer
37
. This read audio data corresponds to one audio frame. The audio decoder
28
then decodes the read audio data.
In order to present images without delays, MPEG defines that an MPEG decoder starts decoding video data only after the video buffer
23
has become full. This generates a time lag between a start of accumulatio
Harumoto Hideaki
Iwasaki Shiro
Okada Tomoyuki
Chevalier Robert
Matsushita Electric - Industrial Co., Ltd.
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