How to convert MIDI to MP3 in your browser

The quickest free way to convert a MIDI file to MP3 is to open midee, drop in the .mid file, open Export, switch to the Audio tab, and click Start. The browser renders the piece with a sampled instrument, encodes it to a 192 kbps MP3, and saves it to your Downloads folder. Nothing leaves your machine. There is no account, no queue, and no watermark or paid tier.

This guide covers the conversion step by step, explains what a MIDI-to-MP3 conversion actually does, lists the choices that change how the result sounds, and is honest about what the browser route cannot do. If you want lossless audio instead, see MIDI to WAV. If you want a video with a scrolling piano roll, see MIDI to MP4.

What a MIDI to MP3 conversion actually does

A .mid file contains no sound. It stores instructions: which note to play, when, how hard, for how long, plus tempo changes and pedal events. An MP3 stores sound. Converting between them means performing the MIDI with an instrument and recording the result. The instrument is the whole story. The same MIDI rendered through a cheap General MIDI synth and through a sampled grand piano are two different recordings.

midee performs the file with multi-sampled instruments (real recordings of each note, layered by velocity), so a piano MIDI comes out sounding like a piano rather than a 1990s sound card. That is also why the instrument picker is the most important setting on this page.

Convert a MIDI file to MP3 in six steps

1. Open midee in any current browser. Chrome, Edge, Firefox, and Safari all work, on desktop and on mobile.
2. Drag your .mid or .midi file onto the page, or click to browse.
3. Press play and listen. Pick an instrument from the toolbar. Piano is the default. Upright, Digital, Rhodes, Guitar, Violin, Flute, Marimba, Bells, Strings, Pad, Pluck, and Bass are also available.
4. Mute any tracks you do not want in the recording. Muted tracks are left out of the MP3.
5. Click Export, choose the Audio tab, and make sure MP3 is selected.
6. Click Start. A progress bar shows the render. The file saves as yourfile.mp3 when it finishes.

The render runs faster than real time, so a typical song takes a fraction of its own length. You can keep the tab in the background while it works.

What you get

192 kbps CBR is the point where MP3 artefacts stop being audible for most listeners on most material. It keeps a three-minute track around 4 MB, which is small enough to email or attach to a message. If you need the full-quality master, export WAV instead and encode MP3 later in your own tool.

Settings that change the result

Instrument. This is the sound of the recording. Choose it while previewing, before you export. Every track in the file is played with the same instrument. midee does not read General MIDI program changes, so a multi-instrument arrangement (piano plus strings plus bass) will be rendered entirely on whichever instrument you pick.

Track mutes. Use the track panel to silence parts you do not want. This is how to export a single hand, drop a click track, or remove a percussion track. Percussion tracks are not filtered automatically, and drum notes will sound as pitched notes on the chosen instrument, so mute them if the file has any.

Volume. The master volume slider is baked into the render. If your export sounds quiet, raise it before exporting rather than normalising afterwards.

Sustain pedal. Pedal events (controller 64) in the file are honoured. Notes held by the pedal ring out for their full pedalled length, which is what makes piano MIDI sound like a performance rather than a sequence.

Transpose. A transposition set in the app is applied to the render, so the MP3 is in the key you hear. The playback speed control is not applied; the export always runs at the file's own tempo.

How midee converts MIDI to MP3 under the hood

The pipeline is entirely client-side JavaScript and Web Audio:

1. The file is parsed with @tonejs/midi into notes, tempo map, and pedal intervals.
2. The instrument's sample set is decoded once and cached.
3. A Web Audio OfflineAudioContext renders the whole piece at 44.1 kHz, faster than real time. It does not play through your speakers and does not depend on your audio device.
4. The rendered buffer is trimmed to the MIDI's duration and encoded to MP3 in the browser by the LAME encoder compiled to JavaScript. The encoder is loaded only when you pick MP3, so it does not slow down the app for anyone else.
5. The bytes are wrapped in a blob and downloaded.

There is no upload and no server. You can disconnect from the network after the app has loaded and the export still completes. The same offline renderer produces the audio track for MP4 exports, so the MP3 you get here is the same audio you would hear in a video export.

When to use MP3, WAV, or MP4

Limitations to know before you start

• One instrument per export. The whole file is played with the instrument you choose. There is no per-track instrument assignment yet.
• No General MIDI bank. midee ships a curated set of 13 instruments rather than the 128 GM programs. Orchestral or band arrangements will not sound like a GM playback.
• Percussion is not filtered. Mute drum tracks manually.
• 192 kbps is the only MP3 bitrate. For other bitrates, export WAV and encode elsewhere.
• Large files. Very long MIDI files (an hour or more) will render, but the in-memory audio buffer grows with length. If a browser tab runs out of memory, split the MIDI first.

Frequently asked questions

Is the MIDI to MP3 converter really free? Yes. midee is open source. There is no paid tier, no signup, and no watermark or audio tag in the output.

Does it upload my MIDI file? No. Parsing, rendering, and MP3 encoding all run inside your browser tab. Nothing is sent to a server.

Which browsers work? All current desktop and mobile browsers. Unlike video export, MP3 export needs no WebCodecs support, so it also works in Firefox and older Safari versions.

Why does my MP3 sound like a piano when the MIDI has other instruments? Because midee renders every track with the single instrument you select. Choose the instrument that fits the lead part, or mute the tracks that do not suit it.

Can I convert MP3 to MIDI? No. That is transcription, a different and much harder problem. midee only goes from MIDI to audio.

How long does a conversion take? Faster than real time. A short piece finishes in a few seconds, and even long pieces render in a fraction of their playing time. There is no queue.

Can I convert several MIDI files at once? Not in one click. Open and export each file in turn. Batch export is not available.

Does it work offline? The export itself makes no network requests. You do need a connection to load the app and the instrument's sample set, so open the app and preview the instrument first, then you can disconnect and export.

Try it

Open midee, drop in a .mid file, pick an instrument, and export from the Audio tab. If you need the lossless version, the MIDI to WAV page covers the same workflow. For every format midee can produce, see the MIDI converter overview.