Extract audio
Save just the sound of a video.
Drop a video and keep its audio as an M4A, or choose Opus, FLAC or WAV. It happens on your device, so a private recording stays private.
There is no MP3 option: browsers can't make MP3 files, and we don't include a converter that would.
Drop a video here.
Drop a video here.Choose a video.
MP4MOVWEBMMKVNothing leaves this device.
Several files of one kind convert together.
How it works
Drop the video, choose the audio file.
1
Drop the video
A lecture, an interview or a concert recording. MP4, MOV, MKV and WebM are read.
2
Just the sound, M4A
Just the sound is selected and writes M4A. Open Custom for Opus, which makes smaller files, or FLAC and WAV, which keep everything but are large.
3
Save
The sound is saved as its own file, named after the video. The video is not changed.
Measured examples
Copied, not converted.
Four generated clips: one with AAC sound, one with Opus sound in a Matroska file, one with Dolby Digital sound and one with no sound at all.
| Test file | Size | Change | Time | Result |
|---|---|---|---|---|
| 20 s clip, 1080pChrome | 30 MB → 327 kB | 99 percent smaller | 190 ms | Sound stream identical · Copied, no quality lost |
| 20 s clip, 1080pWebKit | 30 MB → 327 kB | 99 percent smaller | 1.8 s | Sound stream identical · Copied, no quality lost |
| 10 s clip, AC-3 soundChrome | 2 MB | Refused: could not open the file | 90 ms | |
| 10 s clip, Opus soundChrome | 1.9 MB → 140 kB | 93 percent smaller | 400 ms | |
| 10 s clip, no soundChrome | 9.4 MB | Refused: could not open the file | 70 ms |
Measured on November 7, 2026 in Google Chrome 157, WebKit (Playwright build, not Safari) 26, on Apple M1 Pro. Times run from pressing Convert to the result being ready, with the page already loaded. Likeness is PSNR against the original: higher is closer, and above 40 dB the difference is hard to see. WebKit here is Playwright's build, which is not Safari. Every test file was generated for these measurements, none is anyone else's work, and each is described on the About page.
The AAC sound of a 30 MB MP4 was copied out in 189 milliseconds in Chrome and 1817 in WebKit, byte for byte, leaving a 327 kB file. The Opus sound had to be converted to AAC. A clip with no sound track, and one with Dolby Digital sound, were both refused.
Facts
What you get.
AAC sound
Copied out of the video untouched: instant, with no loss. We compared the decoded samples to prove it.
Other sound
Converted to AAC with a 192 kb/s budget. Simple sound uses less: our Opus test came out at 109 kb/s.
No MP3
Browsers cannot write MP3 and we do not ship a converter that would. M4A is the substitute that plays almost everywhere.
Length
Matched to within 40 milliseconds in our tests.
Good to know
Copying versus converting the sound.
Whether the sound is copied or re-encoded decides how fast this is and whether anything is lost.
When it is only a copy
Most phone, camera and screen recordings carry AAC sound. Choosing M4A copies it out of the video untouched: instant, no loss. The same applies to Opus in a WebM, FLAC in a FLAC-based video, and plain PCM to WAV.
When the sound is a different codec it is re-encoded, at 192 kilobits per second for M4A, which is clear for nearly everything.
Which format to take
M4A plays on phones, computers and most players of the last decade, although some old car stereos and MP3 players only know MP3. Opus is smaller at the same quality and plays in current browsers and Android; older devices may not play it. WAV and FLAC are for editing and archiving.
Choosing FLAC or WAV for a lossy source does not bring detail back. It only makes the file several times larger.
The MP3 question
Flex Convert does not write MP3. Browsers have no MP3 encoder, and the common open ones come with licence conditions we do not accept for a commercial site. M4A at 192 kb/s is the practical substitute: smaller than MP3 at the same quality, and playable almost everywhere.
When it will not work
Sound in a codec the browser cannot decode, such as Dolby Digital, cannot be re-encoded. A video with no sound track has nothing to extract. Take sound only from recordings you made or have the right to use.
Lectures, talks and clips
Sound-only copies suit what you listen to rather than watch: a recorded lecture, a webinar, a concert you filmed. An hour at 192 kilobits per second is about 86 MB as a re-encode. When the original sound is AAC and gets copied, the file is only as big as the sound inside the video was, often smaller.
If something goes wrong
When it does not work.
Both ways of having nothing to extract end in the same message.
Couldn't open this file
Why: The video has no sound track, or its sound is Dolby Digital or DTS, which a browser cannot decode. We tried both, and the page shows the same general message for each; it has no more specific one yet.
What to do: Check in a player that the video has sound. For Dolby Digital or DTS, use a desktop tool that includes those decoders.