This is an unofficial, uncomplete and (pretty sure) wrong documentation of the RESTful service which powers the League of Legends spectator mode.
This documentation is desgined to be community driven and should be extended by everyone. If you find things missing, add them please!
Riot's spectator mode works by requesting replay data via HTTP form a service. The data is split in chunks which usually contain about 30 seconds of gameplay. Additionally there are key frames which seem to contain more information than a single chunk. They seem to be used to support skipping back in time or for spectators that join the game later.