video format is VP6F. I highly recommend using FFDSHOW [Wikipedia]. Make sure in the decoder configuration that VP6F and FLV1 formats are set to use the LIBAVCODEC decoder (as well as the encoder if you plan on doing any converting/editing). FFDSHOW should be anyone's first (and likely last) codec utility. It's efficient, thorough, and robust.

(I also highly recommend you DON'T install any of the various codec packs out there (ie K-LITE)... most of these contain hacked and sloppily reconstructed codecs that can slow down your system and interfere with other codecs, if they even work at all. Video codecs are the new wild frontier for PCs, and having redundant or poor codecs can take a serious hit on system performance, with multiple core-level decoders competing with each other to decode the same stream. If you already have disparate codecs installed, well, you may be SOL -- they are sometimes nigh impossible to uninstall.)