Multiplexing Audio and Video
You will need to use the Nandub program for this guide. If you installed Gordian Knot already, you should already have this installed in the directory where you have Gordian Knot installed.
First open your avi movie. Then from the video tab select direct stream copy.

Next go to the audio tab and select direct stream copy and also load the mp3 audio file for the movie by selecting

Select direct stream copy and also load the mp3 audio file for the movie by selecting (VBR) MP3 Audio. When you select it, it will allow you to load your MP3 file.
Now all we have to do is save the movie. So save your movie and in a few minutes, your movie will be muliplexed with the audio.