[FFmpeg-user] ffmpeg record from usb webcam give huge sync problem

Carl Eugen Hoyos cehoyos at ag.or.at
Mon Feb 23 19:42:16 CET 2015

Vlăduţ Frăţiman <fratiman.vladut <at> gmail.com> writes:

$ ./ffmpeg -y -f v4l2 -video_size 640x360 -framerate 5 \
> -ts mono2abs -i /dev/video0 \
> -f alsa -ac 1 -i hw:1,0 \

> Input #0, video4linux2,v4l2, from '/dev/video0':
>   Duration: N/A, start: 1424715824.973374

> Input #1, alsa, from 'hw:1,0':
>   Duration: N/A, start: 1424715814.786186

On my system, the start times are nearly identical, 
the difference is <0.02 seconds.
If the difference is constant (when you run ffmpeg 
several times), you can use -itsoffset or the setpts 
filter to correct the timestamps.

I suspect this is an issue with the driver of your 
multimedia (v4l2) device, but I don't know enough 
about this.

Maybe -vsync 0 works better but this would be a 
workaround, not a solution.

Carl Eugen

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