Browse Prior Art Database

Dynamic-GOP for a MPEG-2 Video Compression

IP.com Disclosure Number: IPCOM000123741D
Original Publication Date: 1999-Apr-01
Included in the Prior Art Database: 2005-Apr-05
Document File: 1 page(s) / 96K

Publishing Venue

IBM

Related People

Ngai, AY: AUTHOR [+3]

Abstract

Significant picture quality is observed when a new GOP is employed commencing a new scene. Each input picture is analyzed and a figure of merit is calculated to represent its scene content. A change threshold in the figure of merit is used to identify scene change. The first picture in each scene is coded as I picture and a new GOP is started. If the number of pictures in the preceding GOP is less than the selected GOP size, the GOP is terminated prematurely and its picture coding structure is altered. The alternation of picture type in the terminated GOP is based on the number of leading B pictures prior to the scene change, the length of the truncated GOP and the selected GOP structure. Examples of picture type alternation is summarized in the table below.

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Dynamic-GOP for a MPEG-2 Video Compression

   Significant picture quality is observed when a new GOP is
employed commencing a new scene.  Each input picture is analyzed and
a figure of merit is calculated to represent its scene content.  A
change threshold in the figure of merit is used to identify scene
change.  The first picture in each scene is coded as I picture and a
new GOP is started.  If the number of pictures in the preceding GOP
is less than the selected GOP size, the GOP is terminated prematurely
and its picture coding structure is altered.  The alternation of
picture type in the terminated GOP is based on the number of leading
B pictures prior to the scene change, the length of the truncated GOP
and the selected GOP structure.  Examples of picture type alternation
is summarized in the table below.

   As shown in the table, all the pictures belonging to the
old scene are changed to only reference pictures in the truncated
GOP.  In addition, the new GOP created by the new scene changes the
selected open-GOP to closed-GOP.  The next scheduled GOP returns back
to the previously selected open-GOP structure.

   The bit budget of the created new GOP is adjusted based on
the number of bits used in the last GOP and the number of pictures
shortened in the truncated GOP.

   A dynamic GOP structure allows pictures of the same scene
to be grouped in the same GOP.  The closely related references
within each GOP improves efficiency in predictive coding and
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