3.2.1 • Public • Published

    Web Audio Oscilloscope

    A highly customizable oscilloscope for web Audio that supports any source supported by the browser, and renders on a HTML5 canvas.


    Try The Live Demo

    If you are using v1 and planning to move to v2 or v3, the constructor changes a little bit.


    yarn add webaudio-oscilloscope

    Or you can link this file in your HTML:

    <script src="https://unpkg.com/webaudio-oscilloscope@3.2.1/dist/index.js"></script>

    If you include the script in your HTML file, you'll get a global object called _osc. You can acces the functionalities like: _osc.Oscilloscope.

    Example use:

    First create a canvas element in your page:

    <canvas class="osc" width="120px" height="80px">
    <button class="start">Start</button>

    In your JavaScript File:

    import {Oscilloscope, createAudioContext, getUserMedia} from "webaudio-oscilloscope";
    function startOsc(){
        let ctx = createAudioContext();
        let cvs = document.querySelector(".osc");
        getUserMedia({audio: true})
                // Works with any supported source
                let src = ctx.createMediaStreamSource(stream);
                let osc = new Oscilloscope(ctx, src, cvs);

    This package has an utility function, createAudioContext to create an audio context (to avoid dealing with createAudioContext and webkitCreateAudioContext variations)

    This package also has an utility function getUSerMedia that resolves with a Media stream, or resolves with a null. This deals with the different variations and prefixed versions of the getUserMedia API.

    Since Creating Oscilloscope from mediaStream is a very common user case, There's a shorthand function for this.The above code can also be written like:

    import {MediaStreamOscilloscope} from "webaudio-oscilloscope";
    function startOsc(){
        let cvs = document.querySelector(".osc");
        navigator.mediaDevices.getUserMedia({audio: true})
                let osc = new MediaStreamOscilloscope(stream, cvs);



    import {Oscilloscope} from "webaudio-oscilloscope";
     new Oscilloscope(AudioContext, AudioSource, CanvasElement, AudioDestination, [fft, init,primer]);
    Argument Required Default Description
    audioContext true null The Audio Context to use. See MDN
    AudioSource true null The Audio Source to listen to. See MDN
    CanvasElement true null The HTML5 canvas element to render the Oscilloscope in
    Audio Destination false null The Node to pass the output to. e.g destination or any additional node
    fft false 2048 The fft size for the AnalyserNode. The larger the number the smoother the graph the more resource it will consume
    init false null Function to run on the canvas before starting to draw. Gets called only once before starting the drawing Cycle. See below for details
    primer false null The function that gets caled before every render cycle. Useful for stying the Output

    Oscilloscope from Media Stream:

    It's a common use case to create Oscilloscope from Media Stream, Hence, there's a short form.

    import {MediaStreamOscilloscope} from "webaudio-oscilloscope";
    new MediaStreamOscilloscope(mediaStream, CanvasElement, AudioDestination, [fft, init,primer]); 

    This function takes a mediaStream object instead of an audioContext and audioSource, the rest of the parameters are the same. This also produces an Oscilloscope instance.

    Oscilloscope Methods:


    Starts the oscilloscope. Does not take any arguments. Running start on an already running Oscilloscope does not have any effect.


    Pauses the Oscilloscope on the last frame. Paused Oscilloscope can be started using the start() method. Does not take any arguments. This does not affect the media source. Just pauses the Oscilloscope.


    Resets the oscilloscope canvas. Does not take any arguments. Reset oscilloscope can be started using the start() function. Does not affect the media source.

    Changing the look and feel:

    This directly relate to the highly customizable claim in the title. If you know your way around HTML5 Canvas, You'll feel at home.

    The Oscilloscope can be customized by using, the init and primer arguments in the constructor. If you need one of the two, just pass null for the other one. It will be ignored.

    init() [Function]:

    If you want to change the colors or line width of the oscilloscope, use a custom init function. Oscilloscope background is filled with the fillStyle property of the canvas 2d context, and strokeStyle property affetcs the graph color.

    You can create a function like the one below and pass it in the constructor. In fact this is the default init function. You can do stuff like setting the default fill and stroke colors,setting line width etc. For example, to set the fill and stroke style of the canvas:

    function customInit(context, width, height){
        ctx.fillStyle   = "#000";
        ctx.strokeStyle = "#0f0";
    // Then Initiate the Oscilloscope like this:
    new Oscilloscope(AudioContext, AudioSource, CanvasElement, AudioDestination, 2042, customInit);

    primer() [Function]:

    This function gets called before every render. If you need to draw anything (a graph or maybe some values), you can do it here. For example: the default primer function fills the background with the default fill color(black):

    function customPrimer(ctx, width, height){
    // Then Initiate the Oscilloscope like this:
    new Oscilloscope(AudioContext, AudioSource, CanvasElement, AudioDestination, 2042, null, customPrimer);

    For example: If you want to render your oscilloscope on a graph, try this primer function:

    function fancyGraph(ctx,width,height){
        let backstrokeStyle = ctx.strokeStyle;
        ctx.strokeStyle = "#444";
        for(let i=0; i<width; i+=10){
        for(let j=0; j<height; j+=10){
        ctx.strokeStyle = backstrokeStyle;
    // Then Initiate the Oscilloscope like this:
    new Oscilloscope(AudioContext, AudioSource, CanvasElement, AudioDestination, 2042, null, fancyGraph);

    both The function exacly gets 3 arguments, context (The canvas rendering context), width (the canvas width), height (the canvas height). You don't need to worry where these values will come from, just assume that they will be available in the function context.


    You can write plugin for this using the init and primer functions.


    This package is released under the MIT license Feel free to contribute.

    Made with 🖤 and JS.


    npm i webaudio-oscilloscope

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