How hack into a video file as to see all the tracks?

What i mean by this is that say you download a video from youtube. The video has 3 tracks: voice, backround music, and the mp4 file. If you put this video into a viewer you see the mp4 file but also the voice and the backround music mixed together as the audio file. I'm wondering if you can in a way dissect the video file as to see all the tracks from the editing process before they were merged together and uploaded. Maybe there's an application that can do this. I'm pretty sure this is possible because i've seen other people get a hold of the most unlikely mp3s.