Sorry to resurrect an old post.
For anyone who has a Fushicai USBTV007 Video Grabber, here is how to correct your brightness and inherently fix the lack of detail through ffmpeg.
Parameter:
-vf eq=brightness=-0.1
Example, 5 second recording:
ffmpeg -f v4l2 -standard PAL -thread_queue_size 512 -i /dev/video0 -vcodec libx264 -preset superfast -crf 10 -s 720x576 -r 25 -t 5 -aspect 16:9 -vf eq=brightness=-0.1 out.mkv
As someone posted earlier, it is not possible to adjust the controls for this device using v4l2-ctl.
Here is a comparison using someone's Wii: