What happens when I upload a multi-audio video to YouTube? I livestream video game tournaments. The videos I record have two audio tracks. The first track is a low-volume game sound, combined with commentary audio. The second track is just the normalized volume game sound.

When I upload this video to YouTube, what is going to happen? Will YouTube combine both audio tracks into a single track? Will it throw out track 2?

Has anyone done this before?
Youtube will encode the primary or default audio stream.

Youtube doesn't support multiple audio streams. Neither does Vimeo.

Although, apparently, some videos like the 2012 Olympic streams did have it. Special handling by Youtube, I'm sure.