Free converter · Extract audio
Convert MKV to MP3
Short answer
Drop your MKV file into the converter below and download the MP3 file. It runs in your browser with FFmpeg, for files up to 100 MB; nothing is uploaded. Only the sound is kept: the video track is dropped and the audio is saved as MP3 audio at about 128 kbps, keeping the source's sample rate.
Maximum file size: 100 MB. The first conversion loads a ~30 MB converter engine, once per visit. Nothing is uploaded - conversion runs on your device.
Extract audio from MKV into MP3. · Extract audio · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- MKV often holds several audio tracks. FFmpeg's default selects the audio stream with the most channels, which is not always the first track.
- Measured: an MKV with a stereo track first and a 6-channel track second gave an MP3 of the 6-channel track, mixed down to stereo.
- The output is 128 kbps MP3: 161,236 bytes for 10 seconds.
- To pick a track yourself, use ffmpeg with -map 0:a:N.
Measured: the multi-track gotcha
Measured on the soundtrack of a 10 second excerpt of Big Buck Bunny (animated film; (c) Blender Foundation, CC BY 3.0), stereo, 48 kHz, using the same ffmpeg arguments this converter passes to its WebAssembly build, run with ffmpeg 6.1.1. Results describe this file.
We built an MKV with track 1 stereo AAC and track 2 6-channel AAC and converted it with the converter's arguments (-vn, no stream mapping).
| Check | Result |
|---|---|
| Streams in the MKV | video, stereo audio (track 1), 6-channel audio (track 2) |
| Stream ffmpeg chose | Track 2, the 6-channel one |
| Output | MP3, 128 kbps, 2 channels, 161,236 bytes |
FFmpeg's documentation states the rule: for audio, the default selection is the stream with the most channels. If your MKV has a main surround track and a stereo commentary track, you get the surround one.
MKV vs MP3
| MKV | MP3 | |
|---|---|---|
| Full name | Matroska | MPEG-1 Audio Layer III |
| What is inside | Almost any codec, plus several audio and subtitle tracks | MP3 audio |
| Compression | Depends on the codec inside | Lossy |
| Best for | Archiving and playback in desktop players; most social platforms do not list it | Music and podcasts that must play on every device |
What you get
MP3 audio at about 128 kbps, keeping the source's sample rate. Extract audio from MKV into MP3.
Choose the track
- List the tracks:
ffprobe -hide_banner in.mkvand read the Stream lines. - Pick the second audio track:
ffmpeg -i in.mkv -map 0:a:1 -vn -codec:a libmp3lame -qscale:a 2 out.mp3. - Language tags help:
ffprobe -v error -show_entries stream=index:stream_tags=language -of csv=p=0 in.mkv.
What this converter cannot do for you
It has no track picker; it converts the stream ffmpeg selects. If the wrong language comes out, use the terminal command above or remux the MKV to MP4 and check the order.
Questions people ask
Is this MKV to MP3 converter free and private?
Yes. It is free, needs no account and runs entirely in your browser, so the file never leaves your device.
Will converting MKV to MP3 reduce quality?
The audio is re-encoded to MP3, a lossy format, so there is a small loss compared with the original track.
Is there a file size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit; larger files are better handled by a desktop app such as HandBrake or FFmpeg.
Which audio track does MKV to MP3 convert?
The one with the most channels, per ffmpeg's default stream selection, not necessarily the first.
How do I choose another track?
Use ffmpeg with -map 0:a:N, where N counts audio tracks from zero.
What is the MP3 quality?
128 kbps, constant bitrate, with this converter's defaults.
Does it keep surround sound?
No, MP3 output is mixed down to stereo.
More converters
Sources and how we checked
- MDN: Media container formats
- MDN: Web audio codec guide
- MDN: Image file type and format guide
- FFmpeg documentation: stream copy
- FFmpeg Documentation: ffmpeg (stream selection, -map, -c copy) (read 2026-10-08)
- FFmpeg Wiki: Encode/MP3 (libmp3lame quality and bitrate) (read 2026-10-08)
- Blender Foundation: Big Buck Bunny (CC BY 3.0), the clip used for the measurements (read 2026-10-08)
Reviewed October 8, 2026. What the converter writes was measured with ffprobe on the same FFmpeg build your browser downloads; format descriptions follow MDN's media guides.