On Thursday, May 26, 2022, Phyllis Smith via Cin <cin@lists.cinelerra-gg.org> wrote:

Checked these 2 into GIT after testing.  About the following:

Instead "h264_vaapi.mkv" gives me error and no rendering.

Error message popup:
"error rendering data"

On terminal:
FFMPEG::encode_activate: write header failed /home/paz/vaapi_test.mkv
  err: Invalid data found when processing input
Render::render_single: Session finished.

I added a message to the format to state that the mkv "only works on computer that has vaapi capable software and hardware".  I got the same error message as Andrew on my AMD laptop that does not handle vaapi, but an old HP laptop has it working.  Not exactly sure that is the correct reason but it is all I could think of.  Correct me if I am wrong.

may be mkv muxer in ffmpeg more strict (or buggy)? 

if you try to re-mux vaapi-encoded h264 mp4 into mkv with ffmpeg -i file.mp4 -c:v copy (..other params) file.mkv - does it work?