[FFmpeg-user] Adjusting libavdevice/v4l2.c to support V4L2 controls

Goetz Dapp goetz.dapp at googlemail.com
Thu Jul 5 21:48:36 CEST 2012

On 05/22/2012 12:33 AM, Carl Eugen Hoyos wrote:
> Goetz Dapp <goetz.dapp <at> googlemail.com> writes:
>> I am not a programmer and thus at a loss as to how to get that into
>> libavdevice/v4l2.c as suggested. Could you help me out with that or
>> provide me with further pointers?
> I am sorry, but I currently have no access to my hardware that has a 
> v4l2 device, meaning I cannot work on this atm.
> You could try to add ioctl's to device_init() in libavdevice/v4l2.c, 
> it should be easy to add options once that works. If you are unable 
> to test this, you will have to wait until somebody works on it...
> (Please consider opening a ticket on trac, you may point to these 
> mailing list threads, but do add all information into trac.)
> Sorry, Carl Eugen
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Hi everybody, I just wanted to bump this one more time to see if anybody
can help me with this. I will also open a ticket on trac - just haven't
had the time to yet :)

Just to reiterate, my question (see below) was whether it was possible
to adjust ffmpeg to support v4l2 controls:
> ffmpeg -f video4linux2 -framerate 30 -video_size hd720 -input_format
> mjpeg -fflags igndts -an -i /dev/video0 -c:v copy -an /HDD2/test1.mjpeg
> I am curious though if there is any way of controlling the v4l2 control
> ids through ffmpeg, i.e. things like V4L2_CID_WHITE_BALANCE_TEMPERATURE,

No, but I believe it should be straight-forward to implement, see 
v4l2_set_parameters() and options[] in libavdevice/v4l2.c

> The autofocus particularly kicks in during recording and messes things up.
> I also have another problem, namely that I am getting tons of errors
> "/Application provided invalid, non monotonically //increasing dts to muxer"


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