mixing in new music in a DVD->MP4 rip

[brett]

I've been doing P90X this winter. I've got the DVDs, but I ripped them to MP4 (AVC with 2.0 AAC audio) so I could play them on my phone, iPod, Roku box, and PS3.

I figured while I was doing that I wanted to change the boring background music. This should be easy because the DVDs have a separate 2.0 AC3 audio track without the music, so I can just take that track and mix new music in.

So I've already ripped all 13 DVDs with Handbrake into AVC with a 2.0 AAC track and the 192k 2.0 AC3 track (with no audio).

I'm making playlists in WinAmp for the music I want for each DVD. I can use the WinAmp diskwriter plugin to save the whole playlist as a single audio file.

I can then use SoundForge (or something else, who knows) to mix the new music with the original AC3 track. But I don't need to use something fancy as long as I can mix two tracks together and set a delay for when the music starts.

I then need to encode the new track into 2.0 AAC. Then I can use MP4Box or something to remux the new AAC as the primary audio track.

I'm just wondering if there's something I'm not thinking of. I'll bet there is a tool out there that can make this a lot simpler. I haven't really kept up with this stuff for the past few years.

Thanks!