Memory control in trick play mode

Details Memory control in trick play mode Memory control in trick play mode

1998-02-17

2001-04-24

Nguyen, Huy (Department: 2615)

Motion video signal processing for recording or reproducing

Local trick play processing

With randomly accessible medium

C386S349000, C386S349000

Reexamination Certificate

active

06222979

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the reproduction of a digitally encoded signal from a medium and in particular to the allocation of memory during trick mode operation.
BACKGROUND OF THE INVENTION
The introduction of disks recorded with digitally compressed audio and video signals, for example, utilizing MPEG compression protocols, offers the consumer sound and picture quality virtually indistinguishable from the original material. However, consumer users will expect such digital video disks or DVDs to offer features similar to those of their analog video cassette recorder or VCR. For example, a VCR may reproduce in either forward or reverse directions at speeds other than the recorded speed. Such non-standard speed playback features are also known as trick play modes. The provision of trick play features are less easily provided with MPEG encoded video signals due to the hierarchical nature of the compression which forms pictures into groups having varying degrees of compression. These groups are termed groups of pictures or GOPs, and require decoding in sequence. A detailed description of the MPEG
2
standard is published as ISO/IEC Standard 13818-2. However, in simple terms, an MPEG
2
signal stream may comprise three types of pictures having varying degrees of content compression. An intra-coded frame or I frame has the least compression of the three types and may be decoded without reference to any other frame. A predicted frame or P frame is compressed with reference to a preceding I or P frame and achieves greater degree of compression than an intracoded frame. The third type of MPEG frame, termed a bi-directionally coded or B frame, may be compressed based on predictions from preceding and/or succeeding frames. Bi-directionally coded frames have the greatest degree of compression. The three types of MPEG frames are arranged in groups of pictures or GOPs. The GOP may for example contain 2 frames arranged as illustrated in FIG.
1
A. Since only an intra-coded frame is decodable without reference to any other frame, each GOP may only be decoded following the decoding of the I frame. The first predicted frame or P frame, may be decoded and stored based on modification of the stored, preceding I frame. Subsequent P frames may be predicted from the stored preceding P frame. The prediction of P frames is indicated in
FIG. 1A
by the curved, solid arrow head lines. Finally, bi-directionally coded or B frames may be decoded by means of predictions from preceding and or succeeding frames, for example, stored I and P frames. Decoding of B frames by predictions from adjacent stored frames is depicted in
FIG. 1A
by the curved, dotted arrow head lines.
The hierarchical nature of the coded frames comprising MPEG groups of pictures necessitates that the I and P frames of each GOP are decoded in the forward direction. Thus, reverse mode features may be provided by effectively jumping back to an earlier, or preceding I frame and then decoding in a forward direction through that GOP. The decoded frames being stored in frame buffer memories for subsequent read out in reverse to achieve the desired reverse program sequence.
FIG. 1B
illustrates play back in the forward direction at normal speed and at a time prior to time t
0
, a reverse three times speed mode trick play mode is selected. The trick play mode is initiated at time t
0
where I-frame I(
25
) is decoded and displayed. The next frame required for decoding is I-frame I(
13
), thus the transducer is repositioned, as indicated by arrow J
1
to acquire frame I(
13
). Having recovered and decoded I-frame I(
13
), the transducer tracks, as indicated by arrow J
2
to acquire and decode frame P(
16
). The process is repeated as indicated by arrows J
3
, J
4
. Following the acquisition and decoding of frame P (
22
) the transducer is moved as depicted by arrow Jn to recover frame I (
1
). To smoothly portray scene motion requires the decoding and display of I, P, and possibly B-frames. The jump and play process is repeated for preceding GOP, thereby progressing haltingly backwards through the records whilst smoothly portraying the program material in a reverse sequence at the video output.
The provision of visually smooth reproduction during trick mode reproduction requires timely disk retrieval and access to specific pictures from memory. Although each digital disk is encoded with navigation data which provides picture access points within each video object unit, these are limited in number, and may inherently contribute to temporally aliased image motion. To achieve temporally smooth trick mode reproduction, at multiple speeds in forward and reverse directions requires access to, and decoding of all encoded pictures. Although such performance is attainable at the cost of storage capacity, bit stream analysis and mode specific buffer allocation provides opportunities for improved trick mode reproduction.
SUMMARY OF IN INVENTION
In an inventive arrangement, an apparatus reproduces a digitally encoded signal from a disk medium and comprises a source of a bitstream representative of a digitally encoded signal. A processor is coupled to the bitstream for processing the bitstream to extract at least a first and a second data type represented therein. A memory is controllably coupled to the processor for storing one of the first and a second data types. A controller is coupled to control allocation of the memory, wherein a first reproducing mode the controller allocates the memory for storing the first data type, and in a second reproducing mode the controller allocates the memory for storing the second data type.
In a further inventive arrangement, an apparatus for reproducing a digitally encoded signal from a disk medium, comprises a transducer for the digitally encoded signal. A processor is coupled to receive the digitally encoded signal for processing and generating a picture therefrom. A memory is coupled to the processor for storing the picture. A controller is coupled to control the memory and the processor, wherein a first mode the picture is stored in the memory and in a second mode the picture is sub-sampled and stored in the memory.


REFERENCES:
patent: 5949953 (1999-09-01), Shirakawa et al.
patent: 5970205 (1999-10-01), Nakamura et al.
patent: 6009229 (1999-12-01), Kawamura

Affiliated with

Also associated with

Rating

Memory control in trick play mode does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Memory control in trick play mode, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Memory control in trick play mode will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2511874