On Thu, Jun 25, 2020 at 11:21:51PM +0100, Laurence Tratt wrote: > It seems this is because the Logitech C920 has been revised (mine has the > USB ID 046d:0892) and no longer supports a separate H264 mode.
This turns out to be a total red herring -- modern FFmpeg deals with the MJPEG fine and you *can* get it to work for pointlessly small resolutions on OpenBSD. Using this command: ffplay -f v4l2 -input_format mjpeg -video_size 160x90 -i /dev/video0 one can quickly map which resolutions work and which don't. There is some variation from reboot to reboot, but the approximate summary for MJPEG resolutions is roughly as follows: 160x90 Works 160x120 Works 176x144 Works 320x180 Mostly works 320x240 Sometimes works 352x288 Sometimes works 432x240 Breaks up 640x360 Breaks up 640x480 Breaks up 800x448 Breaks up 800x600 Breaks up 864x480 Breaks up 960x720 Breaks up 1024x576 Breaks up 1280x720 Breaks up 1600x896 Breaks up 1920x1080 Breaks up I can only guess as to why this might be: perhaps OpenBSD's USB stack isn't able to transfer data from the USB device? Or maybe there's a problem in uvideo.c (but I've spent several hours fiddling with it and comparing it to the Linux UVC support: I couldn't find anything obvious)? Or ...? I'm now stuck. If anyone has suggestions, I'm all ears! At a basic level, it would be interesting simply to know if anyone else uses MJPEG mode on a webcam and whether they've experienced video break-up too. Laurie
