Hi, I can only answer on the last part: Qt6 Multimedia module currently uses ffmpeg as backend on all platform except for embedded Linux which might be your case. I suggest you take a look at GStreamer chapter in the Qt Multimedia documentation. There might be stuff in there that could be of interest. Hope it helps

There already a camera application(qtcam) integrated qtquick and v4l2, please try clone the source from the below link, https://github.com/econsysqtcam/qtcam.git Application available in launchpad also for ubuntu 12.04 & 14.04