How to convert mkv video to mp3 — free, no upload
- Step 1Open the converter — Go to Video → MP3 — the same engine handles MKV. FFmpeg-WASM loads once into the page, then runs offline. No account is needed inside the free 50 MB / 30-minute limit.
- Step 2Drop your MKV — Drag the
.mkvonto the dropzone. It's read locally; FFmpeg probes it and shows the detected duration, sample rate, and channels. Nothing uploads. The extension tells FFmpeg to use the Matroska demuxer. - Step 3Pick the bitrate — Use the Bitrate dropdown (the only control): 320 kbps for a music/film MKV, 192 kbps default, 128 kbps for talk content, down to 64 kbps for voice. There's no track-selector or codec choice — it's audio-out-to-MP3.
- Step 4Convert — Click the action button. FFmpeg decodes the MKV's default audio track (whatever codec it is) and re-encodes MP3 with
libmp3lame. Video and subtitle tracks are discarded. Large MKVs take a few minutes because the WASM audio path is single-threaded. - Step 5Check the right track came out — The result panel shows output size and engine. If your MKV has multiple audio tracks (e.g. English + commentary), confirm the default track is the one you wanted — this tool takes
-map 0:a(the first/default), with no picker. - Step 6Download or refine — Save the MP3. If the MKV's audio was loud/quiet, normalise with the loudness normalizer. If you only wanted a scene, trim with the audio trimmer. For a lossless film-score extract, use video-to-wav instead.
MKV audio codec → MP3 conversion behaviour
MKV can carry almost any codec. FFmpeg decodes whatever it finds and re-encodes to MP3. Every path is a single re-encode generation.
| MKV audio codec | Decoded by FFmpeg? | Result |
|---|---|---|
| AAC | Yes | AAC → MP3, one lossy generation (common for ripped MP4-source MKVs) |
| AC3 / E-AC3 (Dolby) | Yes | AC3 → MP3; 5.1 is downmixed by the decoder to stereo for MP3 |
| Opus | Yes | Opus → MP3 re-encode; useful for players that reject Opus |
| Vorbis | Yes | Vorbis → MP3 re-encode |
| FLAC (lossless) | Yes | FLAC → MP3 adds the only generation; prefer video-to-wav for an archive |
| DTS | Usually | Decoded where the WASM build supports it; if not, the job errors — try the AC3/AAC track instead if the MKV has one |
What the MKV conversion keeps and drops
Exactly what FFmpeg's command does to each part of a multi-track MKV.
| MKV component | Behaviour | FFmpeg reason |
|---|---|---|
| Video track (H.264/H.265/VP9) | Dropped | Output is MP3; only audio is mapped |
| Default audio track | Decoded → MP3 | -map 0:a selects the first/default audio stream |
| Additional audio tracks | Ignored | No track-picker UI; only the default track is taken |
| Subtitle tracks | Dropped | Not mapped — MP3 can't carry subtitles |
| Chapters / tags | Tags carried; chapters dropped | -map_metadata 0 copies tags; MP3 has no chapter equivalent here |
| Embedded cover / poster | Carried if present | -disposition:v:0 attached_pic re-attaches a still as MP3 art |
Cookbook
MKV-to-MP3 jobs across codecs and track layouts, with the bitrate chosen and the FFmpeg command that runs locally. The default/first audio track is always the one converted.
AC3 (Dolby) MKV → stereo MP3
A film MKV with a 5.1 AC3 track. You want a stereo MP3 of the audio. FFmpeg's AC3 decoder downmixes 5.1 to stereo as part of the decode.
Source: movie.mkv (AC3 5.1, H.265 video, subs) Bitrate dropdown: 192 kbps · default FFmpeg (in-browser): -i movie.mkv -map_metadata 0 -map 0:a -map 0:v? -c:v copy \ -disposition:v:0 attached_pic -id3v2_version 3 \ -c:a libmp3lame -b:a 192k movie.mp3 Output: movie.mp3 (stereo downmix of the 5.1 source) Video + subtitle tracks discarded.
FLAC-in-MKV: go WAV for the archive, MP3 for portable
A high-quality MKV holds a lossless FLAC soundtrack. To preserve it, extract WAV; only convert to MP3 when you want a small portable copy.
Source: concert.mkv (FLAC 48kHz stereo — lossless) Archive (no loss): video-to-wav -> concert.wav (uncompressed PCM) Portable (one generation): Video -> MP3 320k -> concert.mp3 (~144 MB/hour)
Opus-in-MKV → MP3 for an old player
An MKV uses Opus audio. Your car stereo and an old DAW won't play Opus, so you convert to MP3 for compatibility.
Source: clip.mkv (Opus 48kHz stereo) Bitrate dropdown: 256 kbps FFmpeg decodes Opus -> PCM -> libmp3lame 256k Output: clip.mp3 (plays in legacy hardware/software)
Multi-track MKV — the default track wins
An MKV has English (default), Spanish, and director commentary audio tracks. This tool takes -map 0:a, the default track. If you need a non-default track, that's a different workflow.
Source: show.mkv Track 1: English (default) <-- this is converted Track 2: Spanish Track 3: Commentary Video -> MP3 outputs the English track only (no picker in UI). To target a specific track, you'd need explicit stream mapping outside this tool's single-dropdown interface.
Feature-length MKV on Pro+Media
A 2-hour film MKV is several gigabytes. Pro+Media streams it (100 GB cap, unlimited duration). 128 kbps is plenty if it's dialogue-heavy.
Source: feature.mkv (5.2 GB, AC3, 2:05:00) Tier: Pro+Media (100 GB, unlimited duration) Bitrate dropdown: 128 kbps · podcast Output: feature.mp3 (~120 MB, 2:05:00) Processing is CPU-bound and local — minutes, no upload.
Edge cases and what actually happens
MKV has multiple audio tracks — wrong one extracted
First track usedMKVs frequently carry several audio tracks (languages, commentary). This tool uses -map 0:a, which takes the default/first stream — there is no track-picker in the UI. If the output isn't the track you wanted, the MKV's track order/default flag determined it. Selecting a specific non-default track requires explicit stream mapping outside this single-dropdown tool.
DTS audio track can't be decoded
Possible rejectDTS support depends on the FFmpeg-WASM build. If the DTS decoder isn't included, the job errors on that track. Workaround: if the MKV also carries an AAC or AC3 track (many do), and it's the default, that will convert fine — otherwise the DTS-only MKV can't be converted here.
FLAC source loses quality going to MP3
ExpectedA lossless FLAC track in an MKV is decoded and re-encoded to lossy MP3 — one generation of loss. That's inherent to MP3. For an archive, use the video-to-wav extractor to keep uncompressed PCM, and only make an MP3 for portable listening.
5.1 surround MKV — what happens to the extra channels
DownmixedMP3 is typically stereo. FFmpeg's decoder downmixes a 5.1 AC3/AAC track to stereo during decode, so center/surround/LFE content is folded in. The result is a normal stereo MP3 — the discrete surround channels are not preserved (MP3 isn't the format for that).
MKV exceeds free 50 MB / 30-minute limit
Tier limitFilm and concert MKVs almost always exceed the Free cap. Pro lifts it to 200 MB / 120 minutes; Pro+Media to 100 GB / unlimited duration. Size and duration are independent checks — a long-but-small file can still hit the 30-minute Free limit.
Subtitle and chapter info is lost
By designSubtitles aren't mapped (MP3 can't carry them) and chapter markers are dropped — -map_metadata 0 carries general tags but not Matroska chapters into an MP3 in this path. If you need chapters, MP3 isn't the right target format.
Corrupted MKV / index missing
RejectA partially-downloaded or corrupt MKV missing its cues/index can fail to demux. FFmpeg reports a read error. Re-download or repair the container; this tool can't reconstruct missing structural data.
Very large MKV exhausts browser memory
Resource limitA multi-gigabyte film MKV can run the tab out of memory even within Pro+Media's 100 GB cap, because processing is local and bounded by available RAM. Use a desktop browser, close other tabs, or split the source first.
MKV with cover/poster image attachment
Carried overIf the MKV has an attached cover or poster image, -disposition:v:0 attached_pic re-attaches it as MP3 cover art. A few players misread the disposition and show a placeholder — the audio is unaffected and the art is correctly embedded.
No server conversion path
By designAudio tools are browser-only — there's no /api/v1 audio endpoint or runner. You can't POST an MKV to a JAD server to convert it. Everything runs locally via FFmpeg-WASM, which keeps your downloaded files on your device.
Frequently asked questions
Can it convert any MKV regardless of audio codec?
Almost — AAC, AC3, E-AC3, Opus, Vorbis, and FLAC all decode and re-encode to MP3 cleanly. DTS depends on whether the FFmpeg-WASM build includes the DTS decoder; if not, a DTS-only track errors. Most MKVs carry a codec that works.
Is the MKV uploaded anywhere?
No. The MKV is read locally and processed by FFmpeg 8.1 in WebAssembly. There's no upload and no server-side audio API. Your downloaded file stays on your device.
My MKV has English and Spanish audio — which one gets converted?
The default/first audio track (-map 0:a). There is no track-picker in this tool's UI — it has a single Bitrate dropdown. The track flagged as default in the MKV is the one you'll get. Choosing a specific non-default track needs explicit stream mapping outside this tool.
What happens to a 5.1 surround track?
FFmpeg's decoder downmixes 5.1 to stereo during decode, so the MP3 is a normal stereo file with the surround content folded in. MP3 doesn't preserve discrete surround channels.
Should I convert a lossless FLAC-in-MKV to MP3?
Only for a portable copy. MP3 is lossy, so a FLAC source loses one generation. For an archive, use the video-to-wav extractor to keep uncompressed PCM with no added loss.
Does it keep subtitles or chapters?
No. Subtitles aren't mapped (MP3 can't carry them) and chapter markers are dropped. General container tags are copied via -map_metadata 0, and an embedded cover image is re-attached, but MP3 isn't a format for subtitles or chapters.
How large an MKV can I convert?
Free: 50 MB / 30 minutes. Pro: 200 MB / 120 minutes. Pro+Media and Developer: up to 100 GB with unlimited duration — enough for a feature-length film. Size and duration are checked independently.
Why does converting take a few minutes on a big MKV?
The audio engine runs FFmpeg-WASM single-threaded and the work is CPU-bound. A multi-gigabyte film genuinely takes minutes to decode and re-encode. Nothing uploads — the time is local computation. A desktop browser and faster CPU help.
What bitrate should I pick for an MKV?
320 kbps for music or film soundtracks, 192 kbps (default) for general use, 128 kbps for dialogue-heavy content, 64 kbps for pure voice. All are constant-bitrate via libmp3lame; there's no VBR option.
My MKV is DTS-only and it failed — what now?
If the FFmpeg-WASM build lacks the DTS decoder, a DTS-only MKV can't be converted here. If the MKV also has an AAC or AC3 track and it's the default, that will work. Otherwise you'd need to transcode the DTS track elsewhere first.
Will tags and cover art carry into the MP3?
Yes, when present. -map_metadata 0 copies container tags into an ID3v2.3 header, and -disposition:v:0 attached_pic re-attaches an embedded cover/poster image as MP3 artwork.
Is there a way to convert MKV to MP3 on the server / via API?
No — audio tools have no /api/v1 endpoint or runner. Conversion is browser-only via FFmpeg-WASM, which is what keeps your file local. There's no server path to upload an MKV to.
Privacy first
Every JAD Audio tool runs entirely in your browser via FFmpeg (WebAssembly) and RNNoise. Your audio files never leave your device — verified by zero outbound network requests during processing.