Question about hevc_v4l2m2m and pi4

Can someone explain about the support of the hevc_v4l2m2m codec. I know it depends of HEVC/H.265 stateless support for V4L2 in the kernel. But with kernel 5.10 or 5.11 rc and dtoverlay=rpivid-v4l2 in config.txt, i have no support. ( but ffplay -vcodec h264_v4l2m2m is functional)
ffplay -decoders have the support.

   ffmpeg -decoders | grep v4l2

    V..... h264_v4l2m2m         V4L2 mem2mem H.264 decoder wrapper (codec h264)
    V..... hevc_v4l2m2m         V4L2 mem2mem HEVC decoder wrapper (codec hevc)


  ffplay -vcodec hevc_v4l2m2m -i jellyfish-120-mbps-4k-uhd-hevc-10bit.mkv 
  HANDLER_NAME    : hevc@GPAC0.5.2-DEV-rev565-g71748d7-ab-suite
  [hevc_v4l2m2m @ 0xffff7401c4b0] Could not find a valid device
  [hevc_v4l2m2m @ 0xffff7401c4b0] can't configure decoder
  Failed to open file 'jellyfish-120-mbps-4k-uhd-hevc-10bit.mkv' or configure filtergraph


> v4l2-ctl --list-formats-out -d 10
> 	Type: Video Output Multiplanar
> 	[0]: 'H264' (H.264, compressed)
> 	[1]: 'MJPG' (Motion-JPEG, compressed)

It looks like you are doing everything right according to the guides I have seen except what I have seen is people were compiling a patched ffmpeg to make x265 work.

I have been playing around with kodi 19 that is compiled from popcornmix’s tree he maintains. He is a maintainer for the Raspberry Pi kernel and also contributes to Kodi. His Kodi tree is compiled using ffmpeg source from Kodi.

This Kodi can not be run from from within a DE. One would have to exit the DE with a CTRL-ALT-F3 to get to a terminal login prompt then run Kodi. It plays x265 nicely. The pics below show the video stats. It will not show the video it’s self as it is playing in a terminal and a desktop gui app will not see it.

jellyfish-120-mbps-4k-uhd-hevc-10bit.mkv with HW decoding:

Here is another UHD from a NASA stream I captured off my satellite dish with the frame rate at 60 FPS with HW decoding.

It seems that hevc_v4l2m2m is the statefull interface cf.
and the patched ffmpeg is here :