Browse Prior Art Database

Exact Random Access of Motion Picture Experts Group Files

IP.com Disclosure Number: IPCOM000117058D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 101K

Publishing Venue

IBM

Related People

Gorkani, M: AUTHOR [+2]

Abstract

This invention presents a software for exact random access of frames in a Motion Picture Experts Group (MPEG) file. High video compression is crucial in digital multimedia applications. For example, a single frame of a color video with 352x240 pixel frames at 24 bits per pixel takes up about 250 Kbytes of memory. At a real-time rate of 30 frames per second, a bit rate of 60 Mbits/s is required for transfer of one second of video. Today's CD-ROM technology only provides a transfer rate of about 2.4 Mbits/s. The MPEG standard uses interframe compression, achieving compression ratios of up to 200:1 by storing only the differences between successive frames (1). This high compression allows multimedia applications to be realizable in real-time using much less storage.

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Exact Random Access of Motion Picture Experts Group Files

      This invention presents a software for exact random access of
frames in a Motion Picture Experts Group (MPEG) file.  High video
compression is crucial in digital multimedia applications.  For
example, a single frame of a color video with 352x240 pixel frames at
24 bits per pixel takes up about 250 Kbytes of memory.  At a
real-time rate of 30 frames per second, a bit rate of 60 Mbits/s is
required for transfer of one second of video.  Today's CD-ROM
technology only provides a transfer rate of about 2.4 Mbits/s.  The
MPEG standard uses interframe compression, achieving compression
ratios of up to 200:1 by storing only the differences between
successive frames (1).  This high compression allows multimedia
applications to be realizable in real-time using much less storage.

      Since MPEG achieves this compression by taking the differences
between successive frames, not all the frames are decodable
independently of each other.  There are three types of coded frames
in MPEG compression: "I" or intraframes which are simply coded as
still images, not using any past frames; "P" or predicted frames
which are predicted from the recently reconstructed I or P frame (to
access a P frame, the previous frame from which it was predicted also
has to be decoded); and "B" or bidirectional frames which are
predicted from the closest two I or P frames, one in the past and one
in the future.  To access a B frame, the I or P frames from which the
B frame was predicted have to also be reconstructed.  If the frame to
be reconstructed is a P frame, then the frame from which it was
predicted also has to be reconstructed.  As can be seen, the random
access of these frames becomes quite complicated since a series of
frames have to be decoded before a particular frame can be accessed.

      Another difficulty involves the order of frames in an MPEG
stream.  The original order of frames in a sequence is altered in the
MPEG compression.  The reason for this is that for the B frames, the
I or P frames which it depends on have to be decoded before the B
frame is received.  For example, if the original sequence is
"IBBBBPBBBBI", the resulting MPEG stream will be "IPBBBBIBBBB".  Some
special processing has to be done to find the right corresponding
frame in the MPEG stream.

      So far, the MPEG standard has not provided a solution for fast
random access on the encoding end.  The only concession made is the
division of the frames into the series of Groups of Pictures (GOPs)
where the number of the frames in each GOP is the same.
Theoretically,
these GOPs can be used to make random access easier because they
provide
a...