A .MID file is a Standard MIDI File that stores musical performance data (like notes, velocities, and timing) rather than audio samples. The extension is commonly written as .mid, with .midi being a less common alternative. Here’s a concise breakdown:

• What it is: a container for MIDI events formatted in a standardized way so software and hardware can exchange musical performance data.
• Variants: SMF (Standard MIDI File) comes in Type 0 (single track) and Type 1 (multiple tracks played together). Some tools may reference asynchronous vs synchronous track handling, but the core distinction is Type 0 vs Type 1.
• Structure: a MIDI file typically begins with a header chunk (MThd) describing the file format and timing, followed by one or more track chunks (MTrk) containing the actual MIDI events.
• Use cases: used to transfer musical data between sequencers, DAWs, keyboards, and other MIDI-capable devices; can be played back by software synthesizers or hardware sound modules.
• File extension: .mid is the most common extension; .midi is an alternative but less widely used.
• How to open/edit: compatible with most DAWs (e.g., Ableton Live, Logic Pro, FL Studio), notation software, and some media players that support MIDI playback.

If you need, I can tailor this to a specific context (e.g., how to convert a MIDI file to audio, how to inspect its contents, or how to create a MIDI file in a particular program).