From Adobe's F4V/FLV Technology Center :
As the de facto standard for dynamic
media on the web, Adobe Flash supports
a number of media formats. These
include two core open container
formats for delivering synchronized
audio and video streams: F4V and FLV.
F4V builds on the open standard
ISO/IEC 14496-12:2008 (MPEG-4 Part 12)
ISO base media file format and
supports H.264/AAC–based content. It
has a flexible structure and defines
specific supported codecs and
extensions, facilitating simplified
interoperability across tools,
services, and clients. FLV supports
codecs such as Sorensen Spark and On2
VP6, and encodes synchronized audio
and video streams in the same way as
they are encoded in SWF files.
So the two formats are distinct.
Another useful article is : What is the difference between Flash Video (FLV), F4V and H.264.
