Unofficial AirPlay Protocol Specification
Clément Vasseur (via Frederic Jacobs):
This document describes these protocols, as implemented in Apple TV software version 5.0, iOS 5.1 and iTunes 10.6. They are based on well-known standard networking protocols such as Multicast DNS, HTTP, RTSP, RTP or NTP, with custom extensions.
All these information have been gathered by using various techniques of reverse engineering, so they might be somewhat inaccurate and incomplete.
[...] Link. Nice reference; built mostly on standards. [...]