Hi!
I’m new to Vegas- But do this a lot…
Right click either the video or audio track.
Go to “Group” …. then select “Remove From”
… Then it separates the audio from the video, and you can delete it by itself.
I am using Vegas 10 …. Not sure how different the other versions are from this one.
I cannot help with the format, as this is something I need to know, too 🙁 … Lol