[FFmpeg-user] Synchronizing A/V streams from independent sources?

Francois Visagie francois.visagie at gmail.com
Mon Jun 2 08:20:25 CEST 2014

> -----Original Message-----
> From: ffmpeg-user-bounces at ffmpeg.org [mailto:ffmpeg-user-
> bounces at ffmpeg.org] On Behalf Of Jeff
> Sent: 01 June 2014 17:11
> To: ffmpeg-user at ffmpeg.org
> Subject: [FFmpeg-user] Synchronizing A/V streams from independent
> sources?
> I have two MP4 (H.264 AVC/AAC) A/V files, each with the same content.
> For quality and other reasons, I want to extract the video stream from one
> them and the audio from the other, and mux the extracted streams together
> in another MP4 file, which will be the final product. That much is the
> part! :D
> For some reason, the source file which has my preferred video stream runs
> slightly faster (1:20:32) than the source of my audio stream
> Obviously, these streams cannot be synchronized by shifting the start
> I have, so far, tried 'setpts=PTS*1.xxxxxxxx' to slow and extend the
> but this method introduces jerkiness regardless of whether I choose
> vfr' or 'cfr'. I get better (smooth, natural sounding) results by speeding
up the
> audio with 'atempo=1.xxxxxx' or with
> 'asetpts=PTS*0.9xxxxxxx,aresample=async=5000'.

Have you tried the '-map' option? It enables you to specify which stream to
sync to - you could first try the one and then the other and see if that

> The main problem with stretching the video or shrinking the audio is that
> granularity limitations are preventing a perfect match in running times
> would synchronize the two streams from beginning to end. Is there
> something I am missing, some other approach to take? Something better
> than stretching the one, shrinking the other, and by trial and error
hoping to
> find the point where they match up and synchronize?
> Here are a few more details on my two source streams:
> Video: '25 fps, 25 tbr, 16k tbn, 50 tbc' Recoding this stream (necessary
to use
> 'setpts' and 'vsync') with 'ffmpeg -c:v libx264'
> changes tbn to 12800.
> Audio: 44100 Hz sample rate, 44100 tbn
> Thanks for your help.
> Jeff
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