Adobe FLVCheck tool is available at Adobe labs (Windows only)…
"The Adobe FLVCheck tool allows you to modify FLV files that are
created by non-Adobe technology so that they conform to the Adobe FLV
file specification. Malformed messages inside the FLV file have been
found to disrupt the quality of service when watching Flash Video over
the Macromedia Flash Media Server. To ensure your FLV files are
properly formed, use this FLVCheck tool to check the FLV files before
you let others see them."
Seems targeted to fix FLVs for FMS use, nevertheless may come in handy other times too.