a javascript MIDI/Audio sequencer for your browser
JavaScript HTML CSS
Latest commit b1f8415 Jun 4, 2016 @abudaan added link to qambi
Failed to load latest commit information.
api gh-pages updated Dec 23, 2014
assets added documentation for iOS, updated state of development Jan 28, 2015
css added documentation about storing audio locally plus 2 examples Feb 14, 2015
examples added Track.processMidiEvent() and an on-screen keyboard example May 30, 2016
fonts added gh-pages Dec 23, 2014
js added documentation about storing audio locally plus 2 examples Feb 14, 2015
tools added link to qambi Jun 4, 2016
README.md documentation updated Jan 4, 2015



Heartbeat is a MIDI/Audio sequencer for your browser. Heartbeat has no GUI. It is intended to be used as an engine behind your application. Heartbeat is set up very flexible so you can make any kind of application on top of it; a game, an online DAW, artistic sites, music science experiments and so on. Read more.

So far heartbeat has been used in 2 MusicFirst projects:

key features

  • create MIDI file from scratch
  • import existing MIDI files
  • save MIDI data to a file (SMF 1.0)
  • record MIDI (only in browsers that support the WebMIDI API or have the Jazz plugin installed)
  • play back MIDI via external hardware, virtual MIDI ports or included softsynths or sample player
  • quantize and fixed length functions
  • keep a history of edit actions very easily
  • set the PPQ value of a file or song
  • support for tempo and time signature changes
  • multiple songs can be loaded and played back at the same time
  • MIDI data can be shared or moved across songs, tracks and parts very easily
  • import MusicXML files (in progress)
  • volume and panning controller per track
  • volume controller per song and one master volume output with compression
  • channel effects per track: reverb, panning, autopan and more to come
  • record audio directly in your browser
  • save audio recordings as wav, mp3 or base64 file
  • transpose audio (experimental)
  • support for multiple velocity layers
  • support for control change events: sustain pedal, volume and panning
  • sustained instruments (like organ, stings, pads)
  • keyscaling for release and panning
  • configurable release duration and envelope type
  • support for .sfz format (upto a certain level)
  • instrument samples can be transposed at runtime (experimental)
  • 12 sample based instruments included for the sample player (570MB of samples)
  • 1 simple sinewave synthesizer included as fallback instrument

More documentation can be found here.