AudioBufferSourceNode

AudioBufferSourceNode 没有输入却有一个输出. The number of channels in the output corresponds to the number of channels of the AudioBuffer that is set to the AudioBufferSourceNode.buffer property. If there is no buffer set—that is, if the attribute's value is NULL—the output contains one channel consisting of silence. An AudioBufferSourceNode 只能被播放一次; 也就是说,  AudioBufferSourceNode.start() 只允许执行一次. 如果声音需要再播放一次, 那么就需要再创建一个 AudioBufferSourceNode . Those nodes are cheap to create, and AudioBuffers can be reused across plays. It is often said that AudioBufferSourceNodes have to be used in a "fire and forget" fashion: once it has been started, all references to the node can be dropped, and it will be garbage-collected automatically.

多次调用 AudioBufferSourceNode.stop() 是允许的. 最近一次的调用将替换上一次的调用, granted the AudioBufferSourceNode has not already reached the end of the buffer.

属性

从父级的 AudioNode 继承属性.

AudioBufferSourceNode.buffer

Is an AudioBuffer that defines the audio asset to be played, or when set to the value null, defines a single channel of silence. 

AudioBufferSourceNode.detune

Is a k-rate AudioParam representing detuning of oscillation in cents. Its default value is 0.

AudioBufferSourceNode.loop

Is a Boolean attribute indicating if the audio asset must be replayed when the end of the AudioBuffer is reached. Its default value is false.

AudioBufferSourceNode.loopStart

Is a double value indicating, in seconds, where in the AudioBuffer the restart of the play must happen. Its default value is 0.

AudioBufferSourceNode.loopEnd

Is a double value indicating, in seconds, where in the AudioBuffer the replay of the play must stop (and eventually loop again). Its default value is 0.

AudioBufferSourceNode.playbackRate

Is an a-rate AudioParam that defines the speed factor at which the audio asset will be played. Since no pitch correction is applied on the output, this can be used to change the pitch of the sample.

事件

AudioBufferSourceNode.onended

Is an EventHandler containing the callback associated with the ended event.

方法

从父级的 AudioNode 继承方法. 

AudioBufferSourceNode.start()

Schedules the start of the playback of the audio asset.

AudioBufferSourceNode.stop()

Schedules the end of the playback of an audio asset.

例子

在这个例子中, 我们将会创建一个2秒的缓冲器,并用白噪音填充它, 然后通过AudioBufferSourceNode来播放它.  注释里说明了它的功能.

var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
var button = document.querySelector('button');
var pre = document.querySelector('pre');
var myScript = document.querySelector('script');
pre.innerHTML = myScript.innerHTML;
// Stereo
var channels = 2;
// Create an empty two-second stereo buffer at the
// sample rate of the AudioContext
var frameCount = audioCtx.sampleRate * 2.0;
var myArrayBuffer = audioCtx.createBuffer(2, frameCount, audioCtx.sampleRate);
button.onclick = function() {
  // Fill the buffer with white noise;
  //just random values between -1.0 and 1.0
  for (var channel = 0; channel < channels; channel++) {
   // This gives us the actual ArrayBuffer that contains the data
   var nowBuffering = myArrayBuffer.getChannelData(channel);
   for (var i = 0; i < frameCount; i++) {
     // Math.random() is in [0; 1.0]
     // audio needs to be in [-1.0; 1.0]
     nowBuffering[i] = Math.random() * 2 - 1;
   }
  }
  // Get an AudioBufferSourceNode.
  // This is the AudioNode to use when we want to play an AudioBuffer
  var source = audioCtx.createBufferSource();
  // set the buffer in the AudioBufferSourceNode
  source.buffer = myArrayBuffer;
  // connect the AudioBufferSourceNode to the
  // destination so we can hear the sound
  source.connect(audioCtx.destination);
  // start the source playing
  source.start();
}

规范

浏览器兼容性

[1] As of Chrome 42.0 setting AudioBufferSourceNode.buffer more than once is deprecated. A deprecation message is displayed if the buffer attribute is assigned more than once.

相关页面

• Using the Web Audio API