flv converter - transcodiert (!) nach mp4 oder avi
FLVTool2 can calculate a lot of meta data and insert a onMetaData tag. It can cut FLV files and add cue Points
Perian is a free plugin that enables QuickTime to play almost every popular video format.
LiVES is a Free, Open Source video editor *and* a VJ tool.
MediaPipe is a flexible framework to manipulate media on MacOS X. It allows you to build decoding, filtering, encoding and even streaming pipelines that correspond exactly to your needs.