[FFmpeg-user] Unsynced audio while recording from several sources

[Roger Pack]

does async or vsync options help?

On 4/4/17, Valeriy Shevchuk <shevchuk.valery at gmail.com> wrote:
> Hello, everyone.
> I'm trying to use FFmpeg to record video and 3 audio sources and use it to
> generate 3 different video files - each file should contain the same video
> stream but the different audio stream. The problem is that I got audio sync
> issues. The first audio stream is synced perfectly, but the second one has
> 1 sec lag, and the third one has like 2 sec lag.
>
> I've made a few tests so far and it seems that root cause of the issue is
> initialization time of video/audio devices. So, one device is already
> recording something but the second is still being opened and so on. I've
> tried to change input devices order and after that audio streams still have
> the same issue BUT if before 2nd and 3rd audio streams were some time ahead
> of video, after reordering they became to lag after the audio (audio for
> the same event appears with some delay). So this test confirms my version
> about device initialization times.
>
> But the question still, why the first audio stream is synchronized
> properly, while other 2 are not. and also, how could I overcome this
> issues? Any workarounds and ideas are highly appreciated.
>
> Here is FFmpeg command I'm using and it's output.
>
> ffmpeg.exe -f dshow -video_size 1920x1080 -i video="Logitech HD Webcam
>> C615"  -f dshow -i audio="Microphone (HD Webcam C615)" -f dshow -i
>> audio="Microphone Array (Realtek High Definition Audio)"
>> -filter_complex "[1:a]volume=1[a1];[2:a]volume=1[a2]" -vf
>> scale=h=1080:force_original_aspect_ratio=decrease -vcodec libx264
>> -pix_fmt yuv420p -crf 23 -preset ultrafast -acodec aac -vbr 5 -threads 0
>> -map v:0 -map [a1] -map [a2] -f tee
>> "[select=\'v,a:0\']C:/Users/vshevchu/Desktop/123/111/111_jjj1.avi|
>> [select=\'v,a:1\']C:/Users/vshevchu/Desktop/123/111/111_jjj2.avi"
>
>
> Here is the output:
> https://pastebin.com/A3FL05My
>
> PS. Actually, the issue is exactly the same when I'm not using "tee" muxer
> but writing all the audio streams to one container. So, "tee" isn't a
> suspect.
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