So I had recorded my son playing keyboard for a recital. The audio was recorded via MIDI into GarageBand into QuickTime Player. The video was off my iPhone via EpocCam over USB also into QuickTime Player. I was able to get the audio routing setup via a Multi-Output Device I configured in Audio MIDI Setup.

The video had a slight delay which I didn’t quite notice till after I’d recorded it.

I basically wrote a quick script to generate variations of the recorded movies with delays from 50ms to 500ms in 50ms increments and then just watched each of them to see which appeared most correct for his hands playing the keys and the sound of the notes. It was slightly over 200ms and less than 250ms. 210ms seemed the best.

I have now learned the importance of a clapperboard.

(Originally I was going to record the audio in GarageBand and the video on my phone and join them later, but I was learning as I went and I wanted to see if I could record the two streams together.)