[FFmpeg-user] Unable to sync audio and video

[Nicolas George]

Livio Tenze (12021-02-17):
> No, it is not, because the audio and the video streams come from two
> different sources: one webcam and an external microphone. The starting PTS

Different sources do not mean different timestamps origins. In fact, you
NEED the same timestamps origin if you want to sync.

> values are different for two audio and video sources. How should I  get the
> same origin with this configuration? Please suggest how to treat this case.

Ideally, the documentation of the device you are using should be stating
it. For example:

http://ffmpeg.org/ffmpeg-all.html#video4linux2_002c-v4l2

"Depending on the kernel version and configuration, the timestamps may
be derived from the real time clock (origin at the Unix Epoch) or the
monotonic clock (origin usually at boot time, unaffected by NTP or
manual changes to the clock)."

Unfortunately this is rather the exception than the norm.

If the documentation does not say it, then you need to experiment:
actually look at the timestamps, look at at the actual time when you
capture, do some arithmetic to find the origin, and try to guess what it
corresponds to.

And then propose a patch to document the origin of timestamps for that
particular device.

Regards,

-- 
  Nicolas George
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