Emmy Huang announced the release of SWF version 9 specs, which includes FLV specs, yesterday.

Changes in the SWF specifications from version 8 are relatively minor compared to contents of the new AS3 actionscripts tag: DoABC. ABC (Actionscript ByteCode) format was made available earlier.

As with SWF 8 specs, you need to agree to the license terms, which mainly prohibits you make use of the information to write your own Flash/SWF player. Also the specs does not include information about AMF3 for FLV files.