Merging two audio files for commentary track

[The_Flash]

I have an audio commentary track that I want to add to a DVD. It is not part of the actual retail DVD. This audio file is strictly commentary and contains no dialogue or sound from the actual movie. Is it possible to overlay this commentary onto the DVD's original audio track?

I understand I may need to reduce the volume of the original track before adding the commentary, and I do understand decoding and recoding to AC3, and how to rebuild the DVD once completed. I just have no idea which program to use or how to go about merging the above mentioned. I've considered creating a new audio track with the commentary as the right channel and original audio as the left, but that seems kind of lame. I'd like to do this the right way.

Any assistance, tricks, or ideas would be greatly appreciated.

Incase anyone is curious, the track in question is Mike Nelson's (formerly of MST3K) riff commentary from http://www.rifftrax.com. It's a cool idea they have going, but I'd rather integrate the audio into the DVD rather than play it separately off CD.

[anonymez]

you could use an audio editing app such as the freeware audacity (dunno if it accepts ac3 input though, may have to encode to lpcm wav first)

or avisynth mixaudio(), which iirc allows you to specify volume for each track too

:)

[The_Flash]

Thank you for introducing me to Audacity. After tweaking the volumes of each file a little, the "Mix and Render" option worked great. Thanks for taking the time to respond and help me out.