.mid File Extension

What kind of file is a .mid?

A .mid file is usually a Standard MIDI File (SMF). It stores timed musical instructions such as notes, channels, tempo changes, controller movements, track names, and lyrics. It does not contain a recorded waveform, so a synthesizer, sound bank, or virtual instrument must turn those instructions into sound.¹

The commonly used MIME types are audio/midi and audio/x-midi, although neither currently appears as a registered standards-tree type in IANA's audio registry.² A normal SMF begins with the ASCII signature MThd, or hexadecimal bytes 4D 54 68 64. Track chunks begin with MTrk. Check that structure instead of trusting the filename alone.³

How do I open a .mid on my computer?

Use a digital audio workstation, notation editor, sequencer, or dedicated MIDI player that includes or controls a synthesizer:

• On macOS, Logic Pro opens, imports, and exports SMF formats 0 and 1, and can assign software instruments when it opens a file.⁴
• On Windows, macOS, and Linux, MuseScore can import MIDI for notation and editing.⁵
• Ableton Live on Windows and macOS imports .mid files in SMF formats 0, 1, and 2, though it exports format 0 only.⁶

A web browser's audio player is generally not enough. MIDI browser APIs provide access to connected MIDI devices, but do not supply a built-in synthesizer or sound bank.⁷

Poly support for .mid

Poly stores, syncs, shares, versions, and finds .mid files by name. It does not currently infer MIDI from this suffix, preview the performance, extract events or lyrics, create a transcript, or make the musical content available to the Poly agent.

Download the file and open it in a MIDI-capable application. If you also need playback, content-aware audio search, transcription, or agent listening in Poly, render a separate audio copy and keep the .mid original for editable performance data.

History of .mid

MIDI 1.0 was introduced in 1983 so electronic instruments could exchange performance messages. Sequencers still used incompatible project formats, so the MIDI Manufacturers Association adopted the Standard MIDI File format in 1988 for portable, time-stamped performances.³⁸

The .mid suffix became the familiar short spelling. Standard MIDI Files can use three organizations: format 0 stores one track, format 1 stores simultaneous tracks, and the rarely used format 2 stores independent sequences.⁶

Working with .mid and alternatives

Choose the output according to what must remain editable:

Rendering MIDI to audio is not a simple container conversion. The result depends on the selected instruments, sound bank, effects, and support for controller or System Exclusive data. Listen to the complete render before relying on it. Converting recorded audio back to MIDI is a transcription task and cannot recover the original instructions exactly.