There are 3 repositories under v4l2-m2m topic.
Bootable 64-bit Gentoo image for the Raspberry Pi4B, 3B & 3B+, with Linux 5.4, OpenRC, Xfce4, VC4/V3D, camera and h/w codec support, weekly-autobuild binhost
Fmp4streamer streams your V4L2 camera directly to any browser and media player as MP4 (H264).