AudioBufferSourceNode - Web API 接口参考 编辑

AudioBufferSourceNode 接口继承自AudioScheduledSourceNode ,表现为一个音频源，它包含了一些写在内存中的音频数据，通常储存在一个ArrayBuffer对象中。在处理有严格的时间精确度要求的回放的情形下它尤其有用。比如播放那些需要满足一个指定节奏的声音或者那些储存在内存而不是硬盘或者来自网络的声音。为了播放那些有时间精确度需求但来自网络的流文件或者来自硬盘，则使用AudioWorkletNode来实现回放。

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AudioBufferSourceNode 没有输入却有一个输出，其通道数与其 buffer 属性所指定的 AudioBuffer 相同。如果没有设置 buffer，也就是说 buffer 属性是 null 的话，输出将包含一个无声的单通道（每个采样点均为0）。

一个 AudioBufferSourceNode 只能被播放一次，也就是说，每次调用 start() 之后，如果还想再播放一遍同样的声音，那么就需要再创建一个 AudioBufferSourceNode。庆幸的是，创建该节点的代价并不大，并且想要多次播放声音的话，实际上 AudioBuffer 也可以被重用。事实上，你可以用一种“阅后即焚”的方式来使用这些节点：创建节点，调用 start() 开始播放声音，然后，你甚至不需要再保留这个节点的引用了。声音播放完成之后，垃圾收集器会找个恰当的时机回收资源。

多次调用 AudioBufferSourceNode.stop() 是允许的。如果这时候 AudioBufferSourceNode 还没有到达缓冲区末尾的话，最近一次的调用将替换上一次的调用。

输入数量	0
输出数量	1
频道数量	由相关的 AudioBuffer 定义

属性

从父级的 AudioNode 继承属性.

AudioBufferSourceNode.buffer

是一个 AudioBuffer 它定义了要播放的音频，当设置它的值为0时，它会定义一个静默的单通道。

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

是一个 EventHandler 类型，包含了与 ended 相关联的结束事件。

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.

注意: 你可以 查看在线演示 或 查看源代码.

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();
}

注意: 音频数据解码的例子请查看 AudioContext.decodeAudioData 页面.

规范

Specification	Status	Comment
Web Audio API AudioBufferSourceNode	Working Draft

浏览器兼容性

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

• Desktop
• Mobile

Feature	Chrome	Firefox (Gecko)	Internet Explorer	Opera	Safari (WebKit)
Basic support	14 webkit[1]	23.0 (23.0)	未实现	15 webkit 22	6 webkit
detune property	(Yes)	40.0 (40.0)	未实现	?	?

Feature	Android	Chrome	Firefox Mobile (Gecko)	Firefox OS	IE Phone	Opera Mobile	Safari Mobile
Basic support	未实现	28 webkit[1]	25.0 (25.0)	1.2	未实现	未实现	6 webkit
detune property	未实现	(Yes)	(Yes)	(Yes)	未实现	未实现	?

[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