open mp4 file with quicktime player.
open audio files with quicktime player(if in .wav format encode to .aac first)
click on Edit\copy for audio files.
Then click on File\Edit\add to movie on main video file
And the file extension changes form .mp4 to .mov
It will have multiple audio tracks.
You could switch between audio tracks with just two mouse clicks in itunes
while the video is playing.
And the same file would playback on my ipod.
No need to re-encode the video.
Just encode the audio tracks to aac before you add them to the movie
and it will save with direct stream copy.(one hour movie should save in a few seconds)
Please include vocals only track
I'm guessing you're try to play your video on a PC computer? If you're using Vista you will have a slight audio sync issue if you play an m4v file on your computer using QuickTime. You will still be able to play on your iPod without any issues, but some computer operating systems can have audio sync issues. Once Microsoft releases WMP 12, which will be a free download, the problem will go away. In the mean time we have a work around in our Tutorials that will solve your issue. If you need help just let us know.