FLV (Flash Video) files, when converted to Video Symbols in a SWF file, don’t have any audio. The audio is converted to a streaming sound (and mixed with existing sounds if necessary), which can easily be extracted with ASV.
So in order to extract the audio of a FLV, you would import the FLV to a FLA, create enough empty frames, export the SWF. And then ASV can extract the audio from the SWF*.
Well, this didn’t work for FCS created FLV files. Most of the time they would have the sound in 8k NellyMoser format, which is not supported by SWF format (which is not relevant here though), and Flash just wouldn’t import them as they are. Another consideration was that they may contain hours of audio for which the 16K frame limit of a SWF file might become the practical limit.
We have just released ASVFAF, a free add-on tool for ASV. (Legal users can download the tool from their download page).
ASVFAF, converts FLV files to Flash importable audio FLV files and optionally creates many files containing selected length of audio, and again optionally creates MX or MX 2004 1 fps FLA files with appropriate length of empty frames.
Is this a shameless advertisement? Not to make it sound so, I’m offering 3 copies of the tool free to whoever requests it in the comments to this post. Normally, ASVFAF requires ASV installed but this special version will be able to run standalone.
* Another alternative might be using FLV2SWF, but it costs 199.99 EURO.