Adding an additional audio channel to media?


[H]F Junkie
Feb 16, 2003
So I've purchased some Rifftrax audio from their site and want to add it to the necessary movies so that I can watch and hear their commentary. How can I go about doing this so I can just push play in plex and it's like any other movie? Ideally, I'm trying to do a nice 1080P quality video, and 5.1 surround sound, with their audio track chiming in and the gain on the other channels is lowered so their audio is what is heard more, and then when they are done talking, the movies typical audio returns to normal levels.

I've gotten to where I've extracted the movies audio tracks (5.1 I'm guessing).
I've got their audio track.
I'm using Audacity (Unless there's something better).
I'd like to add their track in and hopefully line it up nicely, then add the audio back in to the movie in a container like mkv or mp4 @ h265.

If you don't know what Rifftrax is:

Which is some of the original members of MST3K:


Staff member
Mar 3, 2018
I've actually done a quick and dirty version of this with MPV (a video player). I wanted to listen to commentary (2.0) and the original track (5.1) at the same time, so I just added " lavfi-complex = '[aid1] [aid2] amix [ao]' " to the config file, and it mixed both tracks in real time. That's just an ffmpeg command, so theoretically you could use it with some kind of encoder or maybe even Plex itself.

Anyway, you can use Staxrip to rip audio files out and put them back in without re-encoding. You can also change the container to whatever you want, and transcode the video if you wish.

Theoretically Audacity should do what you're trying to do, but the only thing that worries me is the surround format. I'm not sure if Audacity can decode/re-encode dolby encoded tracks... I can't look into it now, but I can this weekend, assuming no one else chimes in before then.
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