[XviD-devel] Dropping empty frames ?

Jan Lucas jan at lucas-berlin.de
Tue Apr 22 00:12:48 CEST 2003


Hi !
A lot of resent anime is done at multiple frame rates. Parts of it are
done at 30fps progressive and most is done at 24fps telecined. Also a
lot of frames are done at lower telecined or progressive framerates to
save money.
Some people tried to solve the problem by using this tool:
http://www.kjps.net/user/r2-m2/clare/dtv/120fps.html
(Sorry, Japanese only, but you will get an idea about how it done.)
The tool converts 24fps video to 120fps by inserting 4 "dropped" frames
between each real frame and converts 30 fps video to 120 fps by
inserting 3 dropped frames. After that the video clips are joined
together using VirtualDub or something similar. That solves the problem
but there are a lot of issues associated with this "solution" (I should
have rather said ugly hack.)
a) dropping frames causes problems with quite a lot of players.
b) packed B frames afaik don't work correctly
c) creation of those hybrid files is a very complex job

I heard P and B frames with no change are around ~150 bytes using
regular xvid. Using the scheme above without support for "dropped"
frames would waste quite a lot of space and would also use a lot of CPU
power for nothing. A special support for frames without change would
solve that problem. A plugin could do add the additional frames and do
the ivtc where needed, it could also add a flag to the frames that
should be dropped.
What I'm asking is: Is there already a better solution for coding
"hybrid" 24/30 fps video in xvid ? Are there similiar flags like the
film mode flag in mpeg2 in xvid ? Is there a good way to drop frames
without changing the existing bitstream ? Where to look at the source to
do that ?

Thank you

Jan



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