Convert FLV to MP3 - extract audio
FLV was Flash's video container - dead as a platform, still full of archived content people want the audio out of. Wave copies the audio when it's already MP3 (a remux, seconds; see Remux vs re-encode) and re-encodes cleanly when it's AAC or Speex.
What actually changes
Flash Video files come in two eras: pre-2008 FLVs carried Sorenson Spark or VP6 video with MP3 or Speex audio, and post-2008 FLVs typically carry H.264 with AAC. Wave inspects the audio track and takes the fast path when it can. If the audio is already MP3, extraction is a bit-exact stream copy - no re-encoding, no quality loss, seconds on any laptop.
When the source is AAC or Speex, Wave decodes and re-encodes to MP3 through libmp3lame at VBR around 190 kbps. Because the video track is discarded entirely, extract runs several times faster than a full video conversion. Old FLV podcasts, tutorial videos, and Flash-era webinars are the most common inputs - often with MP3 audio already, which lands in the fast path.
FLV audio evolved with the codec choices. Flash Player 6 (2002) added MP3-in-FLV; Flash Player 8 (2005) added VP6 video and kept MP3 audio; Flash Player 9 (2007) added AAC and H.264. Before AAC arrived, tutorial-video producers writing FLV for the web nearly always paired their video with MP3 audio because MP3 was the format their editing software already used. That is why the fast-copy extract works for such a large share of FLV podcasts and lecture recordings.
Speex was the exception - a narrow-band codec designed for spoken word, used mostly in Flash-based voice-chat applications (early conferencing tools, some game voice chat) and in ripped VoIP recordings. Wave decodes Speex and re-encodes to MP3 at 192 kbps, which is well above the transparency threshold for voice content. The MP3 sounds identical to the Speex source (bandwidth-limited but clear).
Three steps.
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Step 1
Drop the FLV file onto the card.
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Step 2
Pick MP3 as the output format.
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Step 3
Convert and save the MP3.
Answers, specifically.
If my FLV already carries MP3, is it lossless?
Yes - a straight stream copy, byte-for-byte. No decode, no re-encode. That's the fast path Wave takes whenever the source audio is already MP3.
What about the Speex codec - will it decode?
Yes. Speex is bundled in Wave's wasm engine. Speex was designed for voice and has narrow bandwidth by nature; the MP3 will preserve every bit of quality the source had.
Do FLV metadata tags carry over?
Basic ID3 tags (title) are set from the FLV's onMetaData block where present. Flash-specific cue points have no MP3 equivalent and are dropped.
My FLV is a several-hour webinar. Will it fit?
Very likely yes. Audio-only output stays modest - an hour of 192 kbps MP3 is about 85 MB. Wave's per-file ceiling is 8 GB regardless.
Does this download YouTube audio?
No. Wave doesn't fetch anything from the network. If you already have a .flv file on disk, this converts it - the download itself is a separate tool.
What about F4V audio extraction - is it the same as FLV?
F4V audio is almost always AAC (Flash 9-era H.264 pipeline) rather than MP3, so the extract is a re-encode from AAC to MP3 through LAME. Use the same MP3 output option in the widget; drop the .f4v and it converts.
Which era of FLV had the higher-quality audio?
Post-2007 FLVs with AAC audio are typically the highest-quality (128-192 kbps AAC). Pre-2007 FLVs used MP3 at variable bitrates depending on the encoder - anywhere from 64 kbps (small file size) to 320 kbps (music-focused). The MP3 output preserves whichever quality the source had.
Can I extract a podcast that was distributed as an FLV?
Yes. Some podcast platforms in the mid-2000s (Odeo, some corporate feeds) distributed episodes as FLV rather than MP3. Wave extracts the audio into a portable MP3 you can put in any podcast app or podcatcher, at similar file size to a native podcast MP3.