[Ffmpeg-devel] Validity of non-zero PTS

[Michel Bardiaux]

Andy Parkins wrote:
> Hello,
> 
> Quick question: is it valid to purposefully create a stream with a non-zero 
> PTS as the first frame?
> 
> I'm thinking, for example, if you were to extract the middle of a stream - do 
> you have to adjust all the PTS values so that zero is at the beginning?
> 
> Andy
> 
I wont venture opinions on other formats than MPEG1, the one I know best.

The video frames (in video streams) and audio 'superframes' (of 1152; in 
audio streams) dont have timestamps. At best, video groups have a timecode.

The system streams, which mux audio and video, dont have frames, they 
have packets. Some of them have PTS and DTS, some have PTS, some have 
nothing.

And yes, it is perfectly valid to start a timestamp sequence at any 
value. It wraps over at 33 bits anyway. (Other discontinuities than that 
wrapover are best avoided, but decoders should be robust against them, 
and it is not absolutely clear in the standards they are illegal; 
certainly not kosher though)

HaND,
-- 
Michel Bardiaux
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