Blender Git Loki

Make encoded video fps correct with ffmpeg < 4.4

Before the FFmpeg commit: github.com/FFmpeg/FFmpeg/commit/1c0885334dda9ee8652e60c586fa2e3674056586
FFmpeg would use deprecated variables to calculate the video fps.

We don't use these deprecated variables anymore, so ensure that the
duration is correct in ffmpeg versions without this fix.

Reviewed By: Sergey, Richard Antalik

Differential Revision: https://developer.blender.org/D11417