[FFmpeg-user] Output PTS is different from the source

[Maziar Mehrabi]

On Thu, Dec 18, 2014 at 6:00 PM, Christian Ebert <blacktrash at gmx.net> wrote:
>
> * Wesley Wen on Thursday, December 18, 2014 at 15:43:22 +0000
> > I'm transcoding one MPEG2-TS file to MP4, but I noticed the start PTSs of
> > video and audio of the generated MP4 file are different from the source.
> > The first video frame starts at 0, while the first audio PTS is
> negative. I
> > would expect the PTS of source and output should be identical.
>
> Me too, but: https://trac.ffmpeg.org/ticket/3859
>
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Hi,

I believe having negative PTSs and/or DTSs is normal for some codec,
specially those that use B-frames (e.g. h.264). It's the responsibility of
the player (receiver) to know how to interpret these negative values.
One more thing is that when you change the container (for example from mp4
to mpegts or vice versa) you should expect that these PTS/DTS values for a
particular frame change. This is because each container has its own way of
implementing time and time-base...

Regards,
Maziar Mehrabi