Copy pasta is probably less useful for this.

Having done some amount of work on this, I will say that a developer will need an understanding of:

- Makefiles + Autotools build system

- C, C++, and Objective-C

- setting appropriate compiler & linker flags

- Apple frameworks, especially AVFoundation

- general low-level video & audio data

- some amount of cross platform understanding, although this is for a single platform

It took me at least the equivalent of 1 full time week (maybe a few days more) to figure out GEM's build system and add a basic AVFoundationVideo player. Even then, I started by adapting a class from OpenFrameworks, then later rewrote it once I unerstood more of what's going on. I think camera capture and recording will be more difficult.