[FFmpeg-user] problem with audio/video sync after conversion

Dave Bevan dave.bevan at bbc.co.uk
Wed Jun 27 14:45:13 CEST 2012

>> No, it means you have to add -strict -2 to your command 
>> line if you want to use an experimental codec.
>Got it. Okay, that worked ... but still got the same out-of-sync behavior when changing the frame rate.
>> I thought that previously 29.97 failed and 15 worked, was that right?
>No, the other way around. Leaving the original 29.97 frame rate is fine, but converting it to 15 introduces the sync problem.
>I feel like I've reached the end of what I can do without a real diagnosis, so I'll follow up with Adobe and post back if I get an answer.

I'm experiencing the same audio sync issues as you Arlo. Tried aac (with strict) instead of libfaac, the output contained lots of audio aliasing problems (like a really bad codec running at a really low bitrate), so reverted to libfaac.

Interestingly (at least I think so), I'm using a dual-output cmd line (-i <input.mov> <mp4_spec_stuff> output.mp4 <webm_spec_stuff> outout.webm) - my webm files do not exhibit sync problems, but the mp4's do, which tells me that the decoding side that eventually produce raw audio samples that get fed to the encoder chains, is working correctly.

Also experienced audio sync issues with mp4 playback on iOS devices, so the sync problems are, at least in my experience, not just limited to flash players. I've STR also observing sync issues with playback of mp4's in newer browsers that support mp4's in the new <video> tag, but again, not on webm in <video>.

My source files are SD-PAL, so 25fps. I wonder if something in libfaac is always outputting samples-per-frame based on 30000/1001, rather than being flexible depending on actual output framerate ?

Does anyone here have working cmd lines that successfully convert 25fps DV25 files to iOS/mp4 files that do not exhibit audio sync issues? I know a number of people have responded "try this" or "try that" however, it's full cmd examples that are known to actually work from personal experience that would, IMHO, be the most valuable responses to contribute.


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