Okay - I don't do much with mp4 and most often when I encounter it I transcode it to something I'm more comfortable with. One day I'll figure out when and why I might want to get comfy with it.

Even so why can't you just open the file in an editing program that supports your file type and remov/mute audio and render it out as same file type with minimal loss but no more audio? Before rendering you can slice or dice or add different video and/or different sound.

Just trying to learn why that wouldn't be a simple solution.