[FFmpeg-user] Questions for the use of async

Bernd Butscheidt bbutscheidt at yahoo.de
Fri Apr 13 16:48:50 CEST 2012

I recently discovered the option "async" which may solve some issues I have when demuxing ts-stream resulting in audio and video out of sync.
    -async samples_per_second

Some guides in the www suggest using a value a litle bit higher than 1, e.g. 3 or four. Some suggest adjusting the value to the sample rate of the audio, e.g. using 44100 or 48000.
Do I understand it right, that if I want a desync of maybe more than one second to be corrected, I would have to use a even higher value than 44100 or 48000?
Is -async only supposed to work when reencoding the audio or is something even done when demuxing to elemtary audio streams (like ac3 or mp3) by using the option copy as codec. Can it then still fill in empty frames or drop frames to keep the audio in sync to the video output?
Kind regards
Bernd B.

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