Re: Enforcing color profile

[Hans Verkuil <hverkuil@xs4all.nl>]

On 17/08/2020 14:09, Stefan Witzel wrote:
> Hello,
> 
> I am not a V4L developer so if this is not the right place to bring up
> the issue please tell me who to contact instead.
> The page [1] documents a problem with a particular device "Elgato Cam
> Link 4K" which provides various format options among which most software
> does not consciously pick the one which it implicitly expects leading to
> problems. There is a software workaround, transcoding and looping
> through a virtual device and a hardware fix flashing the problematic
> profiles away.
> However it appears to me that the most satisfactory solution is hinted
> at in the sentence
> 
>> I couldn't find any option in V4L to force selection of 'YUYV 4:2:2', so instead
> 
> So my question is: what changes would be necessary to allow v4l2-ctl to
> enforce a particular format and who would be the right person to ask to
> make such changes?

It's there already:

v4l2-ctl -v pixelformat=YUYV

That will do the trick.

If you plug in the device and run 'v4l2-ctl -V', which pixelformat does it
report? I would expect it to be YUYV since that's first in the list.

If apps like Discord pick YU12 instead, then that's weird. That's something that
the application does, and v4l2-ctl won't help with that. I.e., it appears to be
an application bug.

One other alternative is that the device has broken 4:2:0 support, i.e. it reports
these formats, but they don't actually work. You can use qv4l2 or qvidcap to test
if these 4:2:0 formats are working.

Regards,

	Hans


> 
> Best regards,
> Stefan
> 
> 
> [1] https://assortedhackery.com/patching-cam-link-to-play-nicer-on-linux/
>