Create unit tests based on variable FPS video

[scotts]

VideoDecoder can handle variable FPS videos in some scenarios, but doesn't handle them well in other scenarios. We should have some unit tests which use a variable FPS video. We should create a small variable FPS video and check it in. A command that can create one:

ffmpeg -i video.mp4 -vf "setpts=PTS*if((gt(N\,30))\,1\,2)+1/TB" -c:v libx264 -bf 0  var_fps_video.mp4

I think it's fine to use one of the kinds of videos FFmpeg can generate on-the-fly, such as testsrc or mandelbrot.

Everything in VideoDecoder should work in exact seeking mode. It will probably fail in approximate mode.

[XueSongTap]

Can I work on this ?

[scotts]

@XueSongTap, absolutely! Some advice on the test video we create, let's see if we can keep it under 300 KB or so.