Feature Request: Add remuxing

[Noodlez1232]

It'd be very nice to be able to remux (or run any sort of ffmpeg command) after downloading a video, before it gets sent through all the post-processing stuff. The post-processing command is pretty limited in use, since it doesn't give the file name of the downloaded video.

I know it uses ffmpeg to integrate the thumbnail and other info directly into the video, it'd be nice if we could tap into that in the settings to perhaps remux the videos to .mkv or .mp4. Maybe a "ffmpeg extra flags" setting?

[Inrixia]

postProcessingCommand has full access to filePathFormatting as descriped in the wiki

So you can just use that to do whatever you wanted.?