Ayush Mittal authored Feb 23, 2020 and Alexandru Băluț committed Mar 05, 2020

The method is applied to the project video framerate, to the audio rate,
and to the audio channels number. In addition, in the Render dialog it's
applied to the muxer and to the encoder(s).

- The audio widgets should always succeed as we don't allow custom
  values.

- The muxer is allowed to fail as it means it's missing from the current
  system, and maybe the user wants to render using a different one.

- Similarly, we pick the first available encoder if the preferred one
  cannot be found.

- The video framerate is allowed to fail as we allow setting a custom
  framerate.

Fixes #2425