On an Odroid C2, I used to read IP camera stream with ffmpeg without HW decoding, as it was not available yet.
After reading many threads on this forum, regarding hw decoding through ffmpeg, I decided to give a try....but without any success.
First of all, I tried to decode the Sintel.2010.720p.mkv file, and it worked well.
This is the command I used:
ffmpeg -c:v h264_v4l2m2m -i Sintel.2010.720p.mkv -an -vf fps=1 -f image2 -strftime 1 "/dev/shm/cam1_%S.jpg"
(This takes a snapshot every second from the video file)
And I got this output: