Scripting in Javascript / QML.

ES7; qml : property real, etc.

setting the path to a file is possible

Editing code

if there are compilation errors, the edited script won’t be saved.

General syntax

Every script must contain

import Score 1.0

somewhere at the top.

A script defines a javascript object, with :

  • Input and output ports
  • Callbacks that are called either regularly on every tick, or on special events (start, stop, pause, resume).

The smallest valid empty script looks like this:

import Score 1.0
Script {
  tick: function(token, state) { }

The tick function’s two arguments give both timing and contextual information useful for writing algorithms.

Please read the Timing page to understand the timing concepts used in ossia score, in particular how model, physical and musical dates relate to each other.

Token object

Important note: due to the way numbers work in Javascript (that is, double-precision floating point numbers), and due to the timing units, scripts can only be expected to be accurate for representing durations no greater than 147 days.

That is, if a time interval lasts a year, after 147 days the timing values returned by prev_date, date, … may not be accurate anymore. This limit is pushed back to the hard limit of 414 years when using the C++ integer-based API instead.

Note that this does not affect for instance, scores with normal durations which would loop back to the beginning - permanently running installations are safe.


  • previous_date: the model date at which the tick starts.
  • date: the model date at which the tick ends
  • parent_duration: the nominal model duration of the closest parent interval.
  • offset: the model date at which we must start reading from our input.
  • speed: current speed (a multiplicative factor).
  • tempo: current tempo.

  • musical_start_last_signature: what is the position in quarter notes of the closest previous musical signature change to previous_date.
  • musical_start_last_bar: what is the position in quarter notes of the closest previous bar change to previous_date.
  • musical_start_position: what is the position of previous_date in quarter notes.
  • musical_end_last_bar: what is the position in quarter notes of the closest previous musical signature change to date.
  • musical_end_position: what is the position of date in quarter notes.

  • signature_upper: 6 in “6/8”, at the start of the tick.
  • signature_lower: 8 in “6/8”, at the start of the tick.


  • logical_read_duration(): how long are we reading from the model data.

  • physical_start(ratio): at which sample in the output must we start to write.
  • physical_read_duration(ratio): how many samples are we reading from the input ports.
  • physical_write_duration(ratio): how many samples are we writing to the output ports.
  • to_physical_time_in_tick(time, ratio): convert a model time into a physical time.
  • from_physical_time_in_tick(time, ratio): convert a time in physical dates, to a time in model dates.

  • in_range(time): check that the model time given is indeed in the range of this tick.

  • position(): where are we in relation to our parent interval. 0 is the beginning, 1 is the nominal duration. If an interval has a greater max, or is infinite, this will go beyond 1.
  • forward(): is the time going forward in this tick (speed > 0).
  • backward(): is the time going backward in this tick (speed < 0).
  • paused(): is the time going anywhere in this tick (speed == 0). Note that there is a difference between setting the speed to zero, and pressing the “pause” button - in the first case, processes will still keep being executed, just with no duration.
  • get_quantification_date(quant): get a model date if there is a quantification date for the requested quantification in this tick. -1 is returned if there isn’t any.

  • get_physical_quantification_date(quant, ratio): get a physical date if there is a quantification date for the requested quantification in this tick. -1 is returned if there isn’t any.

State object

The state object contains global properties relevant for the whole score execution.


  • sample_rate: explicit.
  • buffer_size: explicit.
  • model_to_physical: the ratio to pass to the token functions going from model to physical dates.
  • physical_to_model: the ratio to pass to the token functions going from physical to model dates.
  • physical_date: how many samples have elapsed since the score has started playing.
  • start_date_ns: the date in nanoseconds when the score started playing.
  • current_date_ns: the current date in nanoseconds.

Example of a value mapper

// Necessary for the Script object. 
// It is also possible to import QtQml 2.15
import Score 1.0

// Create our script object
Script {
  // Define the inputs & outputs - they are sub-objects of the script object
  ValueInlet { id: in1 }
  ValueOutlet { id: out1 }
  FloatSlider { id: slider; min: 10; max: 100; }

  // QML syntax for defining a floating-point constant
  readonly property real my_constant: 1.234

  // This function is called on each tick.
  tick: function(token, state) {
    // has a message been received ? 
    if (typeof in1.value !== 'undefined') {
      // print it in the console

      // transform it with some math operations.
      var newValue = in1.value + slider.value * Math.random() + my_constant;

      // write it in the output
      out1.value = newValue;

  start: function() { console.log("I am called on start"); }
  stop: function() { console.log("I am called on stop"); }
  pause: function() { console.log("I am called on pause"); }
  resume: function() { console.log("I am called on resume"); }

Note: it is also possible to access the list of messages with their precise timing, with values.

Example of an audio generator

import Score 1.0

Script {
  // Declare our inputs & outputs
  FloatSlider { id: in1; min: 20; max: 800; init: 440; objectName: "Frequency" }
  AudioOutlet { id: out1 }
  // Index to keep track of the phase
  property real phase: 0;

  tick: function(token, state) {
    var arr = [ ];

    // How many samples we must write
    var n = token.physical_write_duration(state.model_to_physical);
    if(n > 0) {
      // Computer the sin() coefficient
      var freq = in1.value;

      // Notice how we get sample_rate from state.
      var phi = 2 * Math.PI * freq / state.sample_rate;

      // Where we must start to write samples
      var i0 = token.physical_start(state.model_to_physical);

      // Fill our array
      for(var s = 0; s < n; s++) {
        phase += phi;
        var sample = Math.sin(phase);
        sample = freq > 0 ? sample : 0;
        arr[i0 + s] = 0.3 * sample;

    // Write two audio channels, which will give stereo output by default in score.
    out1.setChannel(0, arr);
    out1.setChannel(1, arr);

Example of a MIDI transposer

See the user library: Presets/JS/transpose.qml

Port types

Properties common to all ports

FloatSlider {
    id: myVariableName  // <- how you refer to it in the javascript Code
    objectName: "The name shown in the score UI"
    address: "foo:/bar/baz" // <- default address used when the object is created


Create an audio input:

AudioInlet { 
    id: in    


var left =;
var right =;

console.log(left[0]); // print the first sample of the first channel 

for (var value in left) { ... }

Create an audio output:

AudioOutlet { 
    id: out

// set the data of channel 0 to the following: 
out.setChannel(0, [0.1, 0.0, 0.2, 0.0, -0.1, 0.0]);


Create a MIDI input:

MidiInlet { 
    id: in    


var messages = in.messages();
for (var message in messages) { 
    // Print the MIDI bytes
    console.log(message[0], message[1], message[2]);

Create a MIDI output:

MidiOutlet { 
    id: out

// push a new message
out.add([144, 64, 127]);

// set & replace all the messages to be pushed
    [144, 64, 127], 
    [144, 68, 127], 
    [127, 30, 0]



ValueInlet {
    id: in


// Print the latest message received

// Iterate through all the messages received for this tick, with their timestamp
for (var message in in.values) { 
    console.log(message.timestamp, message.value);


ValueOutlet { 
    id: out

// Use either

// or 
out.addValue(timestamp, 1.234);


Controls behave exactly like ValueInlet but show up as actual UI controls. They have as such relevant properties: min, max, etc.

FloatSlider { 
    min: 0.0
    max: 1.0
    init: 0.5
IntSlider { 
    min: 0 
    max: 127
    init: 0
Enum { 
    choices: ["foo", "bar", "baz"]
    index: 2
Toggle { 
    checked: true
LineEdit { 
    text: "Hello world"