Descripe the feature and motivation

You can follow my struggle to get ffmpeg to capture from a v4l2 device while accepting my precise options, here: #22622
By including libavdevice and calling avdevice_register_all(); in my own code i was finally able to do it. Anyway, i think that call belongs into the ffmpeg backend (void CvCapture_FFMPEG::init()?).

Additional context

No response