Plus you need to know the format of your source file to design the command correctly. How many audio tracks, is the first video track a thumbnail or the video,

Plus you need to know the format of your source file to design the command correctly. How many audio tracks, is the first video track a thumbnail or the video, are the subtitles tracks forced, etc. And in some situations ffmpeg has some warts you have to go around. Like they introduced recently a moronic change of behaviour where the first sub tracks becomes forced/default irrespective of the original forced/default flag of the source. You need to add "-default_mode infer_no_subs" to counter that.