How to extract image from single-frame h264 mkv file?

Question

ffmpeg -i IMG_9353.JPG -pix_fmt yuv420p -y qqq.y4m
x264 qqq.y4m --preset placebo --tune stillimage --crf 33 -o qqq.mkv

How to extract the picture now? qqq.mkv is non-empty, size depends on "crf" option, but all players (mplayer -vo pnm, ffmpeg -i qqq.mkv -y qqq.ppm, vlc) consider the video as empty and does not show anything at all (not produce any output files).

Answer 1

Gstreamer works in this case

gst-launch filesrc location=qqq.mkv ! decodebin ! pnmenc  ! multifilesink location=r.ppm

If it fails, freezes or fails to produce files with "pnmenc" you can use "pngenc", "y4menc", "jpegenc" and other image codecs for saving.