[Matroska-devel] problems with AVC in Matroska

Moritz Bunkus moritz at bunkus.org
Wed Jan 12 21:23:13 CET 2005


Hey,

> Outside of the whole "idealistic editing" application I see little use
> for references on any MPEG based codec.  All of these formats are
> designed to be container independent and usually the decoder chips
> take care of buffering etc as needed for decoding without any outside
> help.

I totally agree. We can make our lives VERY difficult for VERY little
gain if we insist on correct references.

> I don't really know enough about MP4 to comment on whether the CTTS
> thingy is enough but if it can allow VFR etc. I think it's fine.

The CTTS atom is a "frame timecode offset" atom. Another atom is used
for the PTS of all frames, and CTTS gives the differences between the
PTS and the DTS for each frame. You simply add the two values et voila
-- you have a proper DTS.

For "normal" B frames these timecodes are what we have come to expect
from e.g. MPEG-1/-2/-4 B frame timestamping.

Unfortunately, like I've said, that's all the information we have. As
frames may be out of order *even without B frames* in AVC the CTTS atom
doesn't give us any hint on frame types themselves.

Mosu

-- 
If Darl McBride was in charge, he'd probably make marriage
unconstitutional too, since clearly it de-emphasizes the commercial
nature of normal human interaction, and probably is a major impediment
to the commercial growth of prostitution. - Linus Torvalds



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