[Ffmpeg-devel] Re: [PATCH] PKT_FLAG_B
Mon Jul 31 19:10:37 CEST 2006
On Mon, Jul 31, 2006 at 05:48:25PM +0200, Baptiste Coudurier wrote:
> Uoti Urpala wrote:
> > On Mon, 2006-07-31 at 17:25 +0200, Baptiste Coudurier wrote:
> >> Uoti Urpala wrote:
> >>> If the mov stts atom is supposed to represent dts in the sense "the pts
> >>> of the output frame (if any) that the decoder will output when fed this
> >>> input frame, assuming standard buffering behavior in the decoder" then
> >>> you need to create separate ctts atoms when the decoder will delay the
> >>> stream, even if there are only P frames. You can determine this by
> >>> checking whether pts != dts for any of the frames. If you're currently
> >>> doing this then I think the behavior is most likely correct.
> >>> If it's OK to omit separate ctts atoms as long as pts are monotonous (I
> >>> doubt this is the intended semantics) then you can check directly for
> >>> that condition.
> >> Can you read mov/mp4/3gp specs, please ?
> > No, I don't intend to read all of them. Some spec I looked at seemed to
> > support the first alternative. Do you have reason to believe that
> > something in the specs would mean neither of the alternatives I gave
> > would be appropriate, or that something in them would require PKT_FLAG_B
> > functionality?
> Somehow history has proved me to read the specs before talking, but well...
fully agree here
> I also said I would be really OK for a better alternative and I asked
> you to propose one...
looking at the mov/qt specs i cant find any hits for ctts, do you have
anything more recent which describes ctts?
my feeling though strongly suggests stts == dts, ctts == pts no matter
what frame type
ISO/IEC 14496 composition time (CT) and decoding time (DT) are derived from
the Time to Sample Atoms of which there are two types. The decoding time
is derived in the Decoding Time to Sample Atom decoding time deltas between
successive decoding times. The composition times are derived in the
Composition Time to Sample Atom as composition time offsets from decoding
time. If the composition times and decoding times are identical for every
sample in the track, then only the Decoding Time to Sample Atom is
so for .mp4 ctts==pts and stts==dts no matter which frame type
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
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