4. Load and decode audio files (AudioBufferSourceNode)

18 May 2015

Loading audio files

uses AudioBuffer for short to medium-length sounds
XMLHttpRequest is used to fetch sound files
audio files can be in any format supported by the audio element (eg. wav, mp3, aac, varies on different browsers as well)
var request = new XMLHttpRequest();
request.open('GET', url, true);
request.responseType = 'arraybuffer'; - as audio file data is binary, responseType is set to arraybuffer

Decoding audio files

decodeAudioData
decodes audio file data contained in ArrayBuffer, loaded from an XMLHttpRequest request.response attribute
audioData: ArrayButter containing audio file data
successCallbackis invoked when decoding is finished, representing the decoded PCM audio data
errorCallback is invoked if there is an erro decoding the audio file data
decoded PCM audio data is represented as an AudioBuffer
asynchronously decodes the audio file

Playing sounds

playSound() - called every time a key is pressed or mouse is clicked
start(time) - function to schedule precise sound playback for games and applications

ArrayBuffer

a generic fixed-length container for binary data (bytes)

Codec support

audio coding formats supported by the audio element, on various browsers
Google Chrome: ogg, vorbis, wav, pcm, mp3, aac, opus
Internet Explorer: mp3, aac
Mozilla Firefox: ogg, vorbis, wav, pcm, mp3, aac, opus
Opera: ogg, vorbis, wav, pcm, mp3, aac, opus
Safari: wav, pcm, mp3, aac

One-shot behaviour

an AudioBufferSourceNode acts one-shot, only executes once when called
create new one once it has been .start() and .stop()

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