api - 使用Mozilla音频API创建提示音

Question

我正在研究使用mozilla音频API音调生成器:

  function AudioDataDestination(sampleRate, readFn) {
    // Initialize the audio output.
    var audio = new Audio();
    audio.mozSetup(1, sampleRate);

    var currentWritePosition = 0;
    var prebufferSize = sampleRate / 2; // buffer 500ms
    var tail = null, tailPosition;

    // The function called with regular interval to populate 
    // the audio output buffer.
    setInterval(function() {
      var written;
      // Check if some data was not written in previous attempts.
      if(tail) {
        written = audio.mozWriteAudio(tail.subarray(tailPosition));
        currentWritePosition += written;
        tailPosition += written;
        if(tailPosition < tail.length) {
          // Not all the data was written, saving the tail...
          return; // ... and exit the function.
        }
        tail = null;
      }

      // Check if we need add some data to the audio output.
      var currentPosition = audio.mozCurrentSampleOffset();
      var available = currentPosition + prebufferSize - currentWritePosition;
      if(available > 0) {
        // Request some sound data from the callback function.
        var soundData = new Float32Array(available);
        readFn(soundData);

        // Writting the data.
        written = audio.mozWriteAudio(soundData);
        if(written < soundData.length) {
          // Not all the data was written, saving the tail.
          tail = soundData;
          tailPosition = written;
        }
        currentWritePosition += written;
      }
    }, 100);
  }

  // Control and generate the sound.

  var frequency = 0, currentSoundSample;
  var sampleRate = 44100;

  function requestSoundData(soundData) {
    if (!frequency) { 
      return; // no sound selected
    }

    var k = 2* Math.PI * frequency / sampleRate;
    for (var i=0, size=soundData.length; i<size; i++) {
      soundData[i] = Math.sin(k * currentSoundSample++);
    }        
  }

  var audioDestination = new AudioDataDestination(sampleRate, requestSoundData);

  function start() {
    currentSoundSample = 0;
    frequency = parseFloat(document.getElementById("freq").value);
  }

  function stop() {
    frequency = 0;
  }

我希望此声音先打开500毫秒，然后关闭500毫秒，然后重复直到停止按钮被按下为止。我以为可以通过将样本数量22,050到44,100设置为零来做到这一点。但是，此方法似乎不起作用。我认为这是因为重新填充缓冲区的功能每100毫秒发生一次，但是现在这超出了我的知识范围。任何帮助将不胜感激。

Answer 1

实际上，它似乎对我来说很好用。我这样更改了requestSoundData函数中的循环:

for (var i=0, size=soundData.length; i<size; i++) {
  if (currentSoundSample % 44100 < 22050)
    soundData[i] = Math.sin(k * currentSoundSample);
  else
    soundData[i] = 0;
  currentSoundSample++;
}

样本22,050到44,100被设置为零，这似乎完全产生了您想要的效果。在这里您可以尝试代码: http://jsfiddle.net/95jCt/