Extracting FLV audio is trivial if the encoding is MP3, but not so if NellyMoser ASAO audio codec was used.
It has always been said that "FLV is an ‘end’ format, highly compressed, why would you want to get the compressed video/audio out, use the original source". While there may be other legit reasons for wanting this, for FCS/FMS created FLV files, the original audio source is in NellyMoser format!
The root of the problem is that there are not a lot of applications that can decode the NellyMoser codec. Flash and Flash Player can, though. Our solution was creating a tool that will convert FCS created FLVs to Flash importable FLVs and using Flash to do the conversion.
Though I haven’t tried, another solution was to capture Flash Players decoded audio output on its way to the sound card.
Now, all these trouble are going away because Adobe will make an application that can extract FLV audio available on Adobe Labs site ‘soon’. Here’s what Steve Wolkoff of Adobe posted on FlashComm list: "I’m waiting to find out the next window where we can get these tools up. It should be in the near future (I know that’s way too vague to be of much use, but I really can’t predict more accurately. It should be "soon")". Asa Whillock of Adobe wrote "it’s on the way – we’d rather do things right then do things too quickly." on the same list.
That’s good news indeed! Finally, extracting FLV audio will have a final solution, soon.