Spec Differences

This page is to describe the qualitative and quantitative differences between the Web Audio API and the MediaStream Processing API, in particular with regard to the Use Cases and Requirements established by the Audio WG.

As much as possible, this document is intended to be precise and impartial, e.g. instead of saying that one specification is more closely integrated with the WebRTC API, it should describe what the integration is, and how it works.

Differences At a Glance

This table is based on the Level 1 outlines of each spec.

API Feature	MediaStream	Web Audio
Faster than real-time processing	No	Yes
Native Effects	No	Yes
Audio primarily manipulated through <Audio> tags	Yes	No
Audio primarily manipulated through an Audio-Context	No	Yes
Can load sounds faster than playback	No	Yes
Streams/nodes can contain video & audio data	Yes	No

Differences By Example

This section lists differences between the Web Audio spec and the Media Streams Spec with side-by-side examples.

Reading Data from a Media Element

This example demonstrates how to get audio data, using an <audio> or <video> media element as a source.

Web Audio

  function init(){

    var context         = new webkitAudioContext()
      , mediaElement    = document.getElementById( 'audio-element' )
      , sourceNode      = context.createMediaElementSource( mediaElement )
      , javaScriptNode  = context.createJavaScriptNode(2048)
      , audioData       = document.getElementById( 'audio-data' )
      ;

    var processAudio = function(e){
      var channels = e.inputBuffer.numberOfChannels
        , buffer = e.inputBuffer
        ;

      for(var i=0; i< channels; i++){
        audioData.innerHTML += e.inputBuffer.getChannelData(i)[0] +', ';
      }
    };

    javaScriptNode.onaudioprocess = processAudio;

    sourceNode.connect( javaScriptNode );
    javaScriptNode.connect( context.destination );
  };

MediaStream Processing API

Specification: MediaStream Processing API

Editor: Robert O'Callahan (Mozilla)

Browser Support: Firefox nightlies

Features and Design Decisions

• Native code is deliberately minimal, relies upon JavaScript libraries to provide higher-level functionality

Web Audio API

Specification: Web Audio API

Editor: Chris Rogers (Google)

Browser Support: WebKit trunk, Chrome, Safari nightlies?

Features and Design Decisions

• Native code tries to meet needs of common functionality of platform-level audio APIs