I'm newbie, sorry if my questions are too silly...

I have to demux and mux some videos (same container).
I haven't found programs to do this in batch, so I have to learn how to execute by command line.

I have downloaded FFMPEG Batch AV Converter, is this the right program? Or there are even better (and simpler)?
Is there a tutorial about mux&demux in FFMPEG Batch AV Converter?