After I get MP4 dedup working, FLV files are the next step. Some resources that showed up:Adobe’s Flash Video File format Spec – Use is dubious. Some FLV files I have are ‘traditional’ FLV, which is not mentioned here. The newer filetype is a derivation of MP4, so dedup is already covered by MP4dedup.
Open Source Flash’s FLV header page – Again, use is dubious. My test FLV file has “Metadata Injector (c) Youtube” in the file (or similar, I’m not looking at the hex right now). I see no mention of custom metadata except for “AMF” fields, with link to dead pages.
Gnash’s page on AMF – Googling “AMF” turned up this page, which at least has some discussion on what AMF is.