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10/21/2019: Control a YouTube Video Player with midi messages. To demonstrate, click here and press the Play button. Assign videos to midi notes on the Custom Mappings screen.
  • Mix original tracks from Post Malone, Queen, The Beatles, Led Zeppelin and Pink Floyd. For non-commercial educational use only.
  • Output Audio from our Midi player (or any other audio source) to MP3 or WAV files.
  • Import Audio files, and map them to Midi notes. Includes 11 two-bar Drum Loops.
According to ClassicalArchives.com (the largest classical music site in the world):
"OnlineMidi.com is the ONLY Online Midi Editor."

Hear what it can do:

Complete Control: View and edit the exact Pitch, Velocity, and Duration of every Midi Event. Create glides and stereo pans with pitch bends and controllers. 11 Drum Loops synch to any tempo. Unlimited Tracks: Each Track can be assigned to a different Instrument and Midi Channel; and contain 3-band EQ, Reverb, ADSR Envelopes for Amplitude, Low-pass Filters, & LFO Modulators. Midi Player: You may start playing at any position in the song, and Solo and Mute any Tracks. The event list will scroll to show the next event that will be played.
Easy Note Entry: Notes are added by clicking keys on a virtual synth keyboard. The Step By setting selects the default time distance between notes. Copy Range: Select the Start and End of a Range of notes, and click Copy Range to copy those notes to the same Track, or to any other Track. Edit Range: You may Delete, Transpose, Insert Blank Space, Change Durations, or Change Velocities for the notes in the selected time Range.
Split or Double the Tempo: You may match the Tempo of any Drum Sample, without altering the pitch. For example, if your Midi File is 240 bps, splitting the Tempo will cause all Durations to be split in half, so the Tempo will become 120 bps. Download Midi File: After you create a new Midi File, or edit an existing Midi File, you may Download the Midi File to your computer. Create Unique URL's: This will allow anyone to automatically load your midi files. You can post those URL's on your social network pages, to share your songs with the world.
Microtonal Music: 'Normal' music contains 12 chromatic tones in each octave, and each tone is separated by 1/2 step. OnlineMidi.com allows your sound card or synth to play 48 Microtones per octave, each separated by 1/8 step. You don't have to create custom scales (which can't be transposed), or make any other modifications to your synth. Click the [Microtonal] button on any Track, and add plus signs to raise a pitch by 1/8 steps. For example, G++ is 1/4 step higher than G. The three possible microtones for each note (+, ++, and +++) are sent to three separate midi channels that are raised in pitch by 1/8, 1/4, and 3/8 steps. Click here to see a complete description of the Microtonal features.

The Patterns feature will change the way that you create music.
Imagine entering just two notes, and your entire bass track is created.
And then enter three more notes, and your rhythm guitar track is done.
Patterns are used to create new notes for your entire song (or a time range), which have the same relative position with the chords and keys that you enter. This is exemplified below.
Here are the chord and key changes for Giant Steps by John Coltrane:

Chords BM7  D7GM7 Bb7EbM7    Am7 D7GM7 Bb7EbM7 F#7BM7    
KeysB    G    EbG    Eb     B
PatternB D# D F#G B Bb DEb G Ab BbA C D F#G B Bb DEb G F# A#B D# E F#
If a Pattern of notes was entered as C E F G (relative to the key of C), then the Pattern shown above would be rendered. The four notes are treated as their relative position of 1 3 4 5. This is different than simply transposing, which would cause the Am7 chord to be rendered as A C# instead of A C
This example would be created from the following pattern: C E G A

PatternC E G AE G# B CA C E F#F A C DF# A# C# DG B D E
You will notice that the root, 3rd, and 5th will always match the Chord; but the 6th (which is A in the key of C) is affected by the Key.