[x264-devel] Still struggling with VFR video

[Tomas Carnecky]

After having a little discussion over at mplayer-dev-eng about how DTS
and CTS work, based on that I changed some code in the x264 mp4 muxer
and now it sets DTS to p_picture->i_pts and CTS_Offset to 0. This works
fine for streams without B-Frames. So I'm glad I can produce VFR mp4
videos (even though they are without B-Frames).
But I can't get x264 to produce correct mp4 files with B Frames. Also,
when hacking on the demuxer, I've stubled across some problems with your
code: 'offset' (in set_eop_mp4) can be negative, but that isn't allowed
by the spec (and CTS_Offset is u32). And this indeed happens with my VFR
source video.

Michael Niedermayer explained me how DTS/CTS work in mpeg containers:
for the case of mpeg1, mpeg2 and mpeg4 video there is a very
simle rule how PTS/CTS must be set (no frame reordering CTS=DTS, frame
reordering CTS=DTS for B frames, CTS of non B frames = DTS of next non B
frame)
However, I don't see how this could be properly implemented in x264. In
case of non B frames, the mp4 muxer would need to wait for the next non
B frame to set the CTS offset accordingly. But there is no such caching
in the muxer.

tom

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