This code is kinda old (2011 as I remember) and I used it to fuzz the FLV format. It is semi-intelligent and all the testcases should be easy enough to unfuzz. Bear in mind it needs some cleanup and optimization, but I think it is actually a good place to start writing your own file format fuzzers.

It uses Haxe (http://www.haxe.org) to parse FLV, pydbg to monitor crashes and of course python.

Have fun!