I'm a big fan of listening to humorous commentary tracks along with my favorite movies. Currently the only way to do this is to start one program with the commentary audio file, and another program with the video file, and use audio cues from both tracks to line them up using the seek bars of each interface while you're watching. It's... an experience. Especially frustrating if you need to pause for a second...
This tool allows you to create a new audio track in the video file containing the commentary track merged with an existing audio track from the video. It also allows you to adjust the offset of the commentary track, so you can line it up with the audio in the movie at arbitrary points in case they are not already in sync. The script tries to do this automatically using subtitles and audio analysis, followed by an optional 'fine-tuning' step if you really want it dialed in to the millisecond.
I hope this is useful to anyone else who wants to enjoy these "riff tracks" more easily :)