Support container type selection

[mkjustuk]

Is your feature request related to a problem? Please describe.
Feature enhancement to be able to select either mkv or mp4 as the container for the final mux

Describe the solution you'd like
A switch for dl and also for the yaml file that allows the container type to be selected (mkv or mp4).

Describe alternatives you've considered
Manually doing it with ffmpeg from the separate component files