I managed to make it work. My mistake was to build fbturbo, without libump. I rebuilt libump, and fbturbo, and now it work. I think that was the problem. Still very interesting that it worked at all in some way (it was decoding few frames, and then crashing).
I have used the image from the wiki - xubuntu-xenial-20160421-longsleep-pine64-8GB
on a tested sd card. also ran the scripts from tkaiser's post.
on the bottom line I'm not sure what I should do for running video :-)
I have installed VLC player and the image is lagging (frame is changing every few seconds, sound is good).
will try the videos from libde265.org but since the network is so slow, it will take some time.
Install YouTube App on Android or Remix OS and it plays videos in 1080p much better.
So, I tried few other videos. I tested the sample h265 videos from the link longsleep provided. And they all play very well under Linux with mplayer. the 4k @ 60fps doesn't play very well, it is just too slow. Either to decode or to display. 4k @ 24fps, and full hd are playing just fine. Same with h264.
Still many h264 videos I downloaded, i.e. from youtube, often make the kernel crash, corrupt memory, or crash the driver and makes the overlay stay on screen. Only solution is to reboot or repower the board.
Yeah it is not very resilient against errors or maybe even varios encoding parameters. I suggest using publicly available test Videos and add issues for libcedrus and get involved with development. There are way too few people working or helping with that.