[Hidden-tech] add second audio channel to video on mac

[Jeff Brand]

FFmpeg can definitely do what you need.

https://medium.com/@jmarhee/adding-an-additional-audio-track-to-a-video-with-ffmpeg-75502b00d2fb

The first example on the page linked above should do what you want, though you'll want to make sure the alternate track is in the proper format (possibly AAC) before adding it.

Here's another article that adds metadata for the language - probably useful for supporting players:
https://medium.com/av-transcode/how-to-add-multiple-audio-tracks-to-a-single-video-using-ffmpeg-open-source-tool-27bff8cca30

I would imagine that the pro video editing tools would support this as well but I'm not familiar with them.