MIDI to MP3 Converter — Convert MIDI Music Online Free

This audio synthesis tool converts MIDI (Musical Instrument Digital Interface) files into playable MP3 audio using browser-based sound generation. Unlike standard audio formats, MIDI files contain no actual sound data — they store musical instructions including note pitches, velocities, durations, tempo changes, and instrument program numbers. Converting MIDI to audio requires a synthesizer to interpret these instructions and generate corresponding waveforms.

The converter uses the Web Audio API's OscillatorNode and GainNode to synthesize each MIDI note with a piano-like timbre. The tool first parses the MIDI file structure, extracting header chunks (format type, track count, timing resolution) and track chunks containing the sequence of note-on, note-off, and control change events. Timing calculations convert MIDI ticks to real-time seconds using the file's tempo map, handling tempo changes that may occur throughout the piece.

Audio synthesis runs through an OfflineAudioContext for non-real-time rendering, producing a complete PCM audio buffer. This buffer is then encoded to MP3 format using the lamejs encoder library, which implements the LAME MP3 encoding algorithm in pure JavaScript. The resulting MP3 file preserves the musical arrangement at configurable quality levels while being universally playable on all devices and platforms.