User Guide
Add any video file
MP4, MOV, MKV, AVI, WebM, WMV and FLV all work. The container does not matter — FFmpeg identifies what is inside rather than trusting the file extension.
Let the engine load once
Roughly 30 MB on first use, cached afterwards. Every later conversion in the same browser starts instantly.
Convert
The video is discarded and the audio re-encoded to MP3 at LAME quality V2 (~200 kbps average). Whatever codec the source used — AAC, AC-3, Vorbis, Opus, PCM — the output is a standard MP3.
Note what happens to surround sound
If the source carries 5.1 audio, as many MKV and AVI files do, it is downmixed to stereo. That is a real change, and it is the one case where checking the result matters.
Download
The MP3 works in every player, on every device, with no codec support to worry about.
Need something else?
For WAV, AAC or OGG output use the Video to Audio Converter. To convert between existing audio formats, use the Audio Converter.
About the Video to MP3 Converter
This tool pulls the audio out of a video in any common format and returns an MP3. Where the MP4 to MP3 Converter handles the single most common case, this one is built for the awkward files: the MKV with a DTS track, the old AVI, the WebM download, the WMV from a corporate archive.
Why the file extension does not matter
A video file has two independent properties: the container that wraps it, and the codecs inside. The extension tells you only the first. An .mkv might hold AAC, AC-3, DTS, FLAC, Opus or uncompressed PCM; an .avi might hold MP3 or AC-3; a .webm holds Vorbis or Opus. The MDN media container guide sets out which containers permit which codecs.
FFmpeg reads the actual stream headers rather than trusting the extension, decodes whatever it finds, and re-encodes to MP3. That is why this page can accept a list of formats that would otherwise each need their own converter.
| Source | Audio usually inside | Converts? |
|---|---|---|
| MP4 / M4V | AAC | Yes |
| MKV | AAC, AC-3, DTS, FLAC, Opus | Yes |
| AVI | MP3, AC-3, PCM | Yes |
| MOV | AAC, PCM | Yes |
| WebM | Vorbis, Opus | Yes |
| WMV / FLV | WMA, AAC, MP3 | Yes |
Two things that change, and are worth knowing
Surround becomes stereo. MKV and AVI files frequently carry 5.1 or 7.1 audio. MP3 cannot represent those channel layouts in any player you would actually use, so the audio is downmixed to two channels. Dialogue normally survives well; distinct rear-channel effects are folded into the mix.
Only the first audio track is kept. A film in MKV may carry several language tracks and a commentary. The conversion takes the first one. If you need a specific track, reorder or extract it with a desktop tool first.
Generation loss, honestly
Nearly every source here is already lossy — AAC, AC-3, Vorbis and Opus all discard information at encoding time. Re-encoding to MP3 adds a second pass, and because these codecs make different decisions about what to throw away, the losses do not cancel. The MDN audio codec reference covers how each behaves.
At V2 the result is inaudible for speech and for music on ordinary equipment. The exception is a source that was already heavily compressed — a low-bitrate web stream, say — where the second pass has audible artefacts to work with and can make them worse.
Size and speed
Around 1.5 MB per minute at V2, regardless of how large the video was. A two hour film yields roughly 180 MB of audio whether the source was 700 MB or 8 GB — the video track, which is nearly all of it, is discarded rather than converted.
That discarding is also why this is fast. No frame is ever decoded, so extraction typically runs many times faster than real time.
Privacy and limits
The extraction runs through a WebAssembly build of FFmpeg loaded into the browser tab on first use (about 30 MB, cached afterwards). Nothing is transmitted — there is no upload step and no copy of your file on any server. Because a single-threaded WebAssembly module addresses only about 2 GB of memory, files over 300 MB are rejected and anything above 60 MB warns that it will be slow.
Frequently Asked Questions
Which video formats can I use?
MP4, MOV, MKV, AVI, WebM, WMV and FLV among others. FFmpeg reads the actual stream headers rather than trusting the file extension, so it identifies and decodes whatever audio codec is inside regardless of the wrapper.
What happens to 5.1 surround sound?
It is downmixed to stereo, because MP3 cannot carry those channel layouts in any player you would realistically use. Dialogue normally survives the fold-down well; effects that were distinct to the rear channels get mixed in with everything else.
My film has several language tracks. Which one do I get?
The first one in the file. If you need a specific language or a commentary track, reorder or extract it with a desktop tool before converting.
How does this differ from the MP4 to MP3 Converter?
The encoder is the same. This page is aimed at the awkward containers — MKV with DTS, old AVI files, WebM downloads, WMV archives — while the MP4 page covers the single most common case and also accepts audio files as input.
Will the audio sound worse than the original?
Marginally. Almost every video soundtrack is already lossy, and re-encoding to MP3 adds a second generation whose losses do not cancel out. At V2 this is inaudible for speech and for music on normal equipment, though a heavily compressed source can degrade more noticeably.
How big will the MP3 be?
About 1.5 MB per minute. A two hour film gives roughly 180 MB of audio whether the video was 700 MB or 8 GB, because the picture is discarded rather than converted.
Is the video sent anywhere for processing?
No. The extraction happens inside your browser through a WebAssembly build of FFmpeg. Your file never leaves the device, which is why there is no upload wait even for a large video.
Why is audio extraction so much faster than video conversion?
Because no frame is ever decoded. The video stream — which is almost all of the file — is discarded outright, leaving only the comparatively tiny audio stream to process.
