[FFmpeg-devel] About guess_correct_pts / AVFrame.best_effort_timestamp

[Måns Rullgård]

Michael Niedermayer <michaelni at gmx.at> writes:

> On Wed, Feb 16, 2011 at 05:47:15PM +0000, M?ns Rullg?rd wrote:
>> Martin Storsj? <martin at martin.st> writes:
>> 
>> > On Wed, 16 Feb 2011, M?ns Rullg?rd wrote:
>> >
>> >> Nicolas George <nicolas.george at normalesup.org> writes:
>> >> 
>> >> > L'octidi 28 pluvi?se, an CCXIX, M?ns Rullg?rd a ?crit?:
>> >> >> AVI doesn't have timestamps, so the first decoded frame has PTS 0, and
>> >> >> the following ones increment it by 1/framerate.  Simple.
>> >> >
>> >> > Are you saying that Mr X should put a special case in his code for AVI?
>> >> 
>> >> No, he should put a special case for no PTS on an input frame:
>> >> 
>> >> pts = frame.pkt_pts != AV_NOPTS_VALUE? frame.pkt_pts : prev_pts + 1/framerate;
>> >> prev_pts = pts;
>> >> 
>> >> This code will always work.
>> >
>> > Wouldn't this break for VFR-streams? That is, shouldn't it prefer 
>> > frame.pkt_dts over the calculated pts, if pkt_dts is present (and 
>> > reliable, assuming that all guessing code is disabled).
>> 
>> A VFR stream obviously needs timestamps.
>
> tell that to the ISO-MPEG committee, mpeg-ps does not require timestamps on
> each frame yet allows frames to be displayed for 2,3 and 4 field periods
> effectively creating variable fps.

MPEG allows only a constant base rate, with any field repetitions
explicitly indicated.  There is never any ambiguity.

-- 
M?ns Rullg?rd
mans at mansr.com