Muxing a file simply means to extract individual streams out of existing container files or mix existing streams together into a new container file. For MP4, this can be done with ffmpeg and the -c copy switch. If you don't want to write command line inputs, XMedia Recode is a good, free GUI for ffmpeg. There's a documentation on the website, simply select Direct Stream Copy to avoid reencoding the individual streams.

Muxing a file simply means to extract individual streams out of existing container files or mix existing streams together into a new container file. For MP4, this can be done with ffmpeg and the -c copy switch. If you don't want to write command line inputs, XMedia Recode is a good, free GUI for ffmpeg (only available for Windows). There's a documentation on the website, simply select Direct Stream Copy to avoid reencoding the individual streams.