Commercial product: Moyea FLV Editor Ultimate $49.95 with trial version.
You can trim FLV, merge FLV, split
FLV, replace FLV audio, add metadata
and cue point，save project file for
future editing, transform MP3 to
lossless FLV, etc. It generates HTML/
SWF (with various player skins,
special effects, and preloaders) for
uploading to website and blog.
You can import MP3 and FLV files
encoded with H.264, H.263, Flash 8,
Flash 8 with alpha, Sorenson Spark,
Nellymoser, etc. and export FLV, SWF,
and HTML without any loss of quality.
You can take it as an FLV joiner, FLV
splitter, FLV cutter, FLV trimmer, FLV
to lossless SWF converter, and MP3 to
lossless FLV converter.