Hi @rold, welcome to the forum 
Our old Companion software only has support for H264-encoded video streams. Adding support for additional / alternative encoding options requires modifying the software (some more discussion here).
If you use the latest beta release of BlueOS (instead of Companion) it should be possible to set up an MJPG or YUYV stream while in Pirate Mode, which QGC should be able to display if you use an RTSP stream (instead of UDP). Note that H264 is quite an efficient encoding, so there may be bandwidth issues when using an alternative.