Yes, I want to read from a video device (webcam).
I tried using MJPEG with the C920 to get the 30fps, but just to check that it wasn’t the decompression that was slowing down everything, I got a logitech Brio that can do 30 fps in YUYV thanks to USB3. Both get about 15fps, in MJPEG, and the Brio also gets 15 fps in YUYV.
Still, that’s half of what the webcam is technically capable, and other applications (such as guvcviewer) manage a solid 30 fps with the C920 and 60fps with the Brio, so there must be some acceleration possible somewhere on my hardware.