FLV to MP3 Converter

Extract the audio from FLV files and save it as MP3. MP3 sound is copied without quality loss and other sound is converted at the bitrate you choose. Your files stay in your browser.

MP3 quality

MP3 sound is copied as it is. Other sound is converted at 192 kbps for stereo and 128 kbps for mono.

Extract the audio from an FLV file

FLV is the Flash Video format. Websites used it for video until Adobe ended support for Flash Player on 31 December 2020, so most FLV files today are old downloads, lecture archives, screen recordings and game clips. Often only the sound matters: a talk, a song or an interview.

This converter opens the FLV in your browser, checks which sound format is inside and saves it as an MP3 file. If the sound is already MP3, it is copied as it is. If it is anything else, it is converted at the bitrate you choose. The video is left out and nothing is uploaded.

What happens to each kind of FLV sound

An FLV file can hold sound in several formats. The converter reads the format first and picks the safest way to reach an MP3 file.

Sound inside the FLVWhat the converter doesEffect on quality
MP3Copies the sound into an .mp3 file without decoding it.None. The audio is identical to the original.
AACConverts it to MP3, or saves it untouched as .m4a when you turn on Keep AAC audio as M4A.Converting to MP3 encodes the sound a second time. Use 192 kbps or more for music, or keep the M4A.
Nellymoser, ADPCM, G.711Decodes the sound and converts it to MP3.These Flash-era voice formats were low quality to begin with. A higher bitrate does not improve them.
PCMConverts it to MP3.The small loss that every MP3 has.
No sound trackStops and tells you before it converts anything.There is nothing to extract.

Which bitrate to choose

A higher bitrate makes a bigger file. It cannot add detail that the FLV does not have. The table shows the space that ten minutes of sound takes.

BitrateGood forTen minutes takes
128 kbpsSpeech, lectures and podcasts.9.60 MB
192 kbpsMusic and mixed sound. This is the default for stereo.14.4 MB
256 kbpsMusic on good headphones or speakers.19.2 MB
320 kbpsThe highest quality MP3 allows.24.0 MB

Match source picks 192 kbps for stereo and 128 kbps for mono. Voice recorded at 16 kHz or lower gets 64 kbps. MP3 also limits the bitrate for low sample rates: below 32 kHz the top is 160 kbps.

Convert FLV to MP3 with ffmpeg

The converter runs ffmpeg for you. If you prefer the command line, these are the commands it uses. Replace the file names with your own.

FLV with MP3 sound, copied without re-encoding:

ffmpeg -y -i input.flv -map 0:a:0 -c:a copy -id3v2_version 3 output.mp3

FLV with AAC or other sound, converted at 192 kbps:

ffmpeg -y -i input.flv -map 0:a:0 -c:a libmp3lame -b:a 192k -id3v2_version 3 output.mp3
  • -map 0:a:0 picks the first sound track and leaves the video out.
  • -c:a copy copies the sound as it is.
  • -c:a libmp3lame -b:a 192k encodes the sound as MP3 at 192 kbps.
  • -id3v2_version 3 writes tags that older players can read.

Limits to know about

File size

The FLV is read in pieces, so a 5.1 GB file did not fill the memory in our test. The MP3 is built in memory: a 1.3 GB result worked and a 2.6 GB one ran out of memory. Only many hours of sound at a high bitrate come near that.

Speed

On an Apple M1 Mac, one hour of AAC sound became a 192 kbps MP3 in about 25 seconds, and nine hours took about six minutes. Copying MP3 sound takes under a second per hour. Older laptops and phones are slower, and the first conversion also downloads the converter.

Links and online videos

The converter works on files you already have. It cannot fetch an FLV from a web address. Save the file to your computer first, then add it here.

How the FLV to MP3 converter works

This converter runs ffmpeg in your browser through WebAssembly. When you add a file, it reads the start and the end of the FLV to find the sound format, the sample rate and the length. It does not need to read the whole file for that.

If the sound is already MP3, the converter copies it into a new .mp3 file without decoding it, so the audio is identical to the original. If the sound is AAC or an older Flash format, it decodes the sound and encodes it again as MP3 at the bitrate you picked. The video is never touched.

Your browser reads the files and nothing is sent to a server. The first conversion downloads the ffmpeg engine, and the browser keeps it for later visits.

How to convert FLV to MP3

1

Add your FLV files

Drop up to 20 files on the page or choose them on your device. The tool reads each one and shows what sound it holds.

2

Pick the quality

Leave it on Match source to copy MP3 sound untouched. Choose 128, 192, 256 or 320 kbps to convert at a set bitrate.

3

Convert and download

Press Convert to MP3. Play the result on the page, then download each MP3 or all of them in one ZIP.

Example Usage

The sound of a lecture is converted from AAC to MP3. The video is left out.

Input
lecture.flv (101.7 MB, 20:00, AAC)
Output
lecture.mp3 (28.8 MB, 192 kbps)

Frequently Asked Questions

How do I convert FLV to MP3?
Add your FLV file to the page, leave the quality on Match source and press Convert to MP3. The tool saves the sound as an MP3 file that you can play on the page and download. You can add up to 20 files and download them together as a ZIP.
Does converting FLV to MP3 lose quality?
It depends on the sound inside the FLV. MP3 sound is copied without any change, so nothing is lost. AAC and older Flash formats have to be decoded and encoded again, which costs a little quality. Use 192 kbps or more for music, or turn on Keep AAC audio as M4A to avoid the loss.
What is an FLV file?
FLV stands for Flash Video. Adobe made the format for Flash Player, and many sites used it until Adobe ended Flash support on 31 December 2020. An FLV file holds video, usually H.264 or Sorenson Spark, together with sound in MP3, AAC or an older Flash format.
Which MP3 bitrate should I choose?
Use Match source if you are not sure. It copies MP3 sound as it is and converts other sound at 192 kbps for stereo or 128 kbps for mono. Pick 128 kbps for speech and 256 or 320 kbps for music. A higher bitrate cannot add detail that the FLV does not have.
Can I convert FLV to MP3 at 320 kbps?
Yes. Choose 320 kbps and the sound is encoded at that rate. MP3 allows it only for sound at 32 kHz or higher, so audio recorded at a lower sample rate is limited to 160 kbps. The tool tells you when that happens.
Why does the tool say my FLV has no sound?
Some FLV files hold only video, such as screen recordings made without a microphone. The tool checks the file before it starts and tells you when there is no sound track, so you do not wait for a conversion that cannot work. If you expected sound, play the file in VLC to check.
Can I paste a link or a YouTube address?
No. The converter works only on files that are on your device, because a browser tab cannot download videos from other sites. Save the FLV to your computer first and then add it here.
Is my FLV file uploaded to a server?
No. Your browser reads the file and ffmpeg runs on your device through WebAssembly. The only download is the ffmpeg engine, about 32 MB, which the browser keeps for next time.
How big can the FLV file be?
The FLV can be very large. The browser reads it in pieces instead of loading it into memory, so a 5.1 GB file converted in about 15 seconds in our test. What has to fit in memory is the MP3. A nine-hour recording at 320 kbps made a 1.3 GB MP3 in our test, while an 18-hour one, which would have been 2.6 GB, ran out of memory. For a very long recording, pick a lower bitrate.
How do I convert FLV to MP3 in VLC or with ffmpeg?
In VLC, open Media, choose Convert / Save, add the file, pick the Audio - MP3 profile, set a destination and press Start. With ffmpeg, run the command shown on this page. This tool does the same job without installing anything.

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The FLV to MP3 Converter is maintained by CodeItBro. We aim to provide the best free developer tools on the web. If you have feedback or suggestions, please visit our contact page.

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