Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1999-09-15
2004-06-15
Nguyen, Huy (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000
Reexamination Certificate
active
06751400
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for reproducing encoded data compressed in accordance with the MPEG system. More particularly, it relates to a technique of reproduction in a reverse direction in the reproducing method and apparatus.
2. Description of the Related Art
As a compression system for a moving picture exploiting correlation along the time axis across plural frames, an MPEG system (Motion Picture Coding Experts Group System) is being used extensively. For example, the video which has adopted the MPEG system is standardized in ISO-13818-2.
In the MPEG system, intra-frame prediction-coded pictures, which are encoded pictures composed of the information closed in a picture itself, are periodically inserted to enable random accessing, so that there is provided a picture group structure having at least one intra-frame predictive coded picture. This picture group is termed a group-of-pictures (GOP).
An example of the GOP structure in the MPEG system is explained by referring to FIG.
1
.
The MPEG system provides three picture types, namely an I-picture, P-picture and a B-picture. The I-picture is the intra-frame predictive-coded picture, while the P-picture is the inter-frame forward predictive-coded picture, obtained by having reference to a previously coded temporally previous frame. The B-picture is a bidirectionally predictive-coded picture obtained on prediction by having reference to temporally previous and temporally posterior pictures. In the MPEG system, at least one I-picture is contained in one GOP.
FIG. 1
shows an example of such GOP structure.
FIG. 1A
shows the GOP structure in which the respective pictures are arrayed in the sequence of the decoding processing (decoding order), while
FIG. 1B
shows the state in which the respective pictures are arrayed in the sequence of the original pictures (presentation order).
In the example of
FIG. 1
, each GOP is made up of 15 frames, namely a sole I-picture, four P-pictures and 10 B-pictures. In
FIG. 1
, suffix letters to the pictures I, P and B denote the presentation order of these pictures.
In the example of
FIG. 1
, a picture I
2
is encoded by itself, while a picture P
5
is inter-frame predictive-coded by having reference to the picture I
2
. The pictures B
3
, B
4
are inter-frame predictive-coded by having reference to the pictures I
2
and the picture P
5
. Therefore, while the picture I
2
can be decoded by itself, decoding of the picture P
5
needs data decoded from the picture I
2
, while decoding of the pictures B
3
and B
4
need data decoded from the picture I
2
and the picture P
5
.
Since the B-picture, which is the bidirectionally predictive-coded picture, is provided in the MPEG system, the processing order of the encoding processing or the decoding processing differs from the order of the original pictures, as shown for example in
FIGS. 1A and 1B
. Thus, the original moving picture is resumed by re-arraying the respective pictures, decoded in the sequence shown for example in
FIG. 1A
, in a proper sequence shown in
FIG. 1
, and displaying the re-arrayed pictures. Therefore, in order to decode the encoded frames, there is required an operation of sequentially decoding the encoded frames in the correct order taking into account the correlation of the respective pictures I, P and B.
With the data encoded by the MPEG system, there is raised a problem that difficulties are met in reproducing the data in a direction reversed to the time axis direction at an elevated speed by way of performing the reverse direction reproduction. This problem is discussed hereinafter in detail.
If, in the example of
FIG. 1
, reverse direction reproduction is to be made beginning from the picture B
12
, the respective pictures need to be displayed in the order of B
12
, P
11
, B
10
, B
9
, P
8
, B
7
, B
6
, P
5
, B
4
, B
3
, I
2
, B
1
, B
0
, . . . .
However, since it is necessary in the MPEG system to effect decoding sequentially along the time axis direction, the pictures I
2
, P
5
, P
8
, P
11
and P
14
need to be decoded in this order, if e.g., the picture B
12
is to be decoded. If, after the end of decoding of the picture B
12
, the picture P
11
is to be decoded, the pictures I
2
, P
5
and P
8
need to be re-decoded.
If, with the progress in the display, it becomes necessary to decode the picture B
1
, the pictures I
2
, P
5
, P
8
, P
11
and P
14
of the directly previous GOP need to be decoded sequentially, because the last P-picture of the directly previous GOP is required for decoding the picture B
1
.
The processing of sequentially decoding the pictures as from the leading end of a GOP is performed every time the respective pictures are displayed during reverse direction reproduction. Thus, in order to assure a constant displaying interval of the respective pictures, it is necessary to control the speed with the maximum time required in the decoding process. This imposes limitations on the speed of the reverse direction reproduction to render it impossible to effect reverse direction reproduction at an elevated speed.
Also, in decoding encoded data of a picture to be reproduced, it is necessary to start the decoding as from the intra-frame predictive-coded picture lying forwardly of the encoded data of the picture to be reproduced. That is, in decoding the encoded data of the picture desired to be reproduced, it is necessary to sequentially decode the intra-frame predictive-coded picture up to the picture to be reproduced without outputting these pictures to outside. If decoding up to the picture to be decoded has come to a close, the decoded data of the picture to be reproduced is outputted. In effecting reverse direction reproduction, the above-described decoding from the intra-frame predictive-coded picture up to the picture to be reproduced is repeatedly performed each time a sole picture is reproduced.
That is, since it is necessary in the reverse direction reproduction to decode the intra-frame predictive-coded picture up to the picture be reproduced, in an iterative fashion, each time a sole picture is to be reproduced. Therefore, if, in reading out the encoded data recorded on the recording medium by way of performing the reverse direction reproduction, the reverse direction reproduction is to be carried out at an elevated speed, the encoded data needs to be read out iteratively from the recording medium at an elevated speed.
As the recording medium for recording picture data, a disc-shaped recording medium or a tape-shaped recording medium is frequently used. However, limitations are imposed on reading out the data from the recording medium at an elevated speed. Thus, it has been difficult to effect the reverse direction reproduction at an elevated speed because of the necessity of repeatedly reading out the encoded data.
This problem is not only limited to the reverse direction reproduction of the data encoded in accordance with the MPEG system, but also is common to the reverse direction reproduction of the data encoded and compressed by exploiting the correlation along the time axis across plural frames.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a reproducing method and apparatus in which it is possible to realize high-speed reverse direction reproduction of the encoded data comprised of picture data compressed in accordance with e.g., the MPEG system.
The reproducing apparatus according to the present invention is configured for reproducing compressed encoded data by exploiting correlation of picture data along the time axis direction over plural frames. The reproducing apparatus includes decoding means for decoding the encoded data, a frame memory in which to store the picture data decoded by the decoding means, writing means operating so that, in reverse direction reproduction of the encoded data in a direction reversed from the time axis direction, the encoded data of the respective pictures are sequentially decoded, the decoded picture data are sequentially stored in the
Matsumura Yoshiaki
Ogawa Kenji
Okazaki Toru
Frommer William S.
Frommer & Lawrence & Haug LLP
Nguyen Huy
Polito Bruno
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