Ah, hadn't found that. Excellent.

Thanks!
-Zandr

I'm just back from a weekend at the track where I had my iPhone on the dash with the front camera pointed at me, and a GoPro in the windshield. I thought it would be amusing to catch video of my face as I dealt with the craziness of a high-hp car on a wet track. :)

It seems that no matter what I do ...

There are a number of codecs that do support an alpha channel. The "tell" is that they have a 32-bit mode.
An alternative would be to render two video files, one with the gauges and one greyscale file with the alpha channel only.

Thinking out loud, I wonder if Motion or Final Cut could import the ...

Count another user here who would love to see multiple Hero4 support over BT.

I have a Hero4 Black, and should have another one by the end of the month (assuming they ever ship the "Music" edition... sigh)

Thanks,
-Zandr