Open and play a MIDI file in your browser
Drop a .mid file on the player above and it shows every part, the piano roll, the tempo map and the controller data, then plays the notes back. There is nothing to install, and the file is read on your own computer rather than uploaded.
It is built for the moment before a MIDI file goes anywhere: checking an export before you send it to an orchestrator, opening a sketch from a collaborator who uses a different DAW, or finding out why a part imports at the wrong tempo.
What a MIDI file contains, and what it does not
A Standard MIDI File is a list of timed instructions. It records which notes start and stop, how hard each one is played, controller moves such as the mod wheel, program numbers, and the tempo and time signature map. It can also carry track names and markers.
It contains no audio at all. The sound comes from whatever instrument receives the instructions, which is why the same file sounds completely different in two templates.
Why it sounds different from your DAW
The preview here uses a simple synth, with one basic tone per General MIDI instrument family and synthesised drums on channel 10. It is there to check pitches and timing, not to judge orchestration.
In your template, the same notes trigger sampled instruments shaped by keyswitches and continuous controllers. The preview plays notes and velocities only. Keyswitch notes therefore sound as very low or very high pitches, which makes them easy to spot on the roll.
Format 0 and format 1
Format 1 files keep each instrument on its own track, with a shared tempo map. Format 0 files merge everything onto one track and separate the instruments by MIDI channel.
This viewer splits a format 0 file into one part per channel, so both formats read as a list of instruments. Format 1 is the better choice for orchestral work, because track names survive the export.
Reading the controller lane
Pick a part and a controller under the roll to see its data as a line over time. CC1 usually drives dynamics in orchestral libraries, CC11 expression, CC64 the sustain pedal, and CC21 vibrato in many string libraries. Pitch bend is drawn around a centre line.
A flat lane on a sustained part often explains a lifeless mockup. The guide to MIDI CC1, CC11 and the controllers beyond them covers what each one does.
Exporting a clean MIDI file
Export a Standard MIDI File, format 1 where your DAW offers the choice, from the start of the project rather than from a selected region. That keeps the tempo map and bar numbers aligned with the session.
Name every track before exporting. The names carry into the file, and they are how an orchestrator, a notation program or a range checker knows which part is which. The instrument range checker reads those names to match each part to an instrument.
For the programming side, the orchestral mockup guide covers how controllers, velocity and timing turn MIDI into a believable performance.