When editing the video, they give you the option to add an additional audio track. That's when I use the track I've recorded.
You can actually split the audio of the video and replace it by another track.
So you add the video track, split the audio, replace the audio with the track you've recorded directly on the computer.
The one thing you need for a good audio track on the computer is to run your sound through a pre-amp before going into the direct-in jack on the computer. So use either an amp, a powered mixer or a simple effect pad with a built-in preamp (most new ones have them).
