I record game footage and commentary (A 'Let's Play') and recently been playing with recording the commentary in Audacity and adding it into the video separately so I can tweak the commentary separate from the game audio. The recording process is fine, I even figured out an easy way to synch the two up, but when I went to encode this I found my render times a *lot* higher. A 1 hr video with commentary and game audio premixed by Fraps takes a couple of hours or a little bit longer to encode into Main Concept MP4 1600x900 30fps using a two pass method and CUDA. When I added in the second audio track it was closer to 3 and a half hours. I've even tried to preconvert, with Audacity, the commentary track to AAC, so Vegas wouldn't have to convert it, and no change. How do I reduce the rendering time down?
I frequently render all audio in a project to a .wav file. I can then import the rendered file, and use it to replace all existing audio files. Initially, I simply null all of the existing files, but, once I am sure I do not need the original source files, I delete them from the system. That gives me one audio file to adjust and to go into the render process.
BTW, I have never seen an audio render take very much time, but, then again, I always render the audio and video separately for DVD Architect.