Addendum: I remembered that ffplay existed. Annoyingly, it still doesn't properly handle ffmpeg-generated .gif.mkv files by default, but you can do: $ ffplay

Addendum: I remembered that ffplay existed. Annoyingly, it still doesn't properly handle ffmpeg-generated .gif.mkv files by default, but you can do: $ ffplay -codec:v gif -i A.gif.mkv to force correct video codec. Also, it seems this is not a problem with the video players, but rather that ffmpeg's matroska muxer writes a incorrect video codec id of V_QUICKTIME. It works correctly with mov/.gif.mov (and possibly other container formats), and should work with mkv if you can patch in a correct codec id.