I want .flv video. Why do you tell me to use .f4v?
FLV isn't just a file extension — it's a container format used by older Flash Video codecs (H.263 and VP6), which is officially deprecated for H.264 content. If you want H.264 content playable in Flash, you typically want to use a MP4 container format, not FLV. Call it ".f4v" if you like.
It is possible to place H.264 and AAC streams into the traditional FLV file, but Adobe strongly encourages everyone to embrace the new standard file format.