Web Audio API附加/连接不同的audiobuffer并将它们作为一首歌曲播放

Web Audio API append/concatenate different AudioBuffers and play them as one song

本文关键字：播放 一首 附加 API Audio 连接 audiobuffer Web      更新时间：2023-09-26

我一直在玩Web音频API，我试图加载一首歌的多个部分，并将它们附加到一个新的ArrayBuffer，然后使用ArrayBuffer作为一首歌播放所有部分。在下面的例子中，我使用了相同的歌曲数据(这是一个小循环)，而不是歌曲的不同部分。

问题是它仍然只播放一次而不是两次，我不知道为什么。

下载歌曲

function init() {
  /**
   * Appends two ArrayBuffers into a new one.
   * 
   * @param {ArrayBuffer} buffer1 The first buffer.
   * @param {ArrayBuffer} buffer2 The second buffer.
   */
  function appendBuffer(buffer1, buffer2) {
    var tmp = new Uint8Array(buffer1.byteLength + buffer2.byteLength);
    tmp.set( new Uint8Array(buffer1), 0);
    tmp.set( new Uint8Array(buffer2), buffer1.byteLength);
    return tmp;
  }
  /**
   * Loads a song
   * 
   * @param {String} url The url of the song.
   */
  function loadSongWebAudioAPI(url) {
    var request = new XMLHttpRequest();
    var context = new webkitAudioContext();
    request.open('GET', url, true);
    request.responseType = 'arraybuffer';
    /**
     * Appends two ArrayBuffers into a new one.
     * 
     * @param {ArrayBuffer} data The ArrayBuffer that was loaded.
     */
    function play(data) {
      // Concatenate the two buffers into one.
      var a = appendBuffer(data, data);
      var buffer = a.buffer;
      var audioSource = context.createBufferSource();
      audioSource.connect(context.destination);
      //decode the loaded data
      context.decodeAudioData(buffer, function(buf) {
        console.log('The buffer', buf);
        audioSource.buffer = buf;
        audioSource.noteOn(0);
        audioSource.playbackRate.value = 1;
      });
    };
    // When the song is loaded asynchronously try to play it.
    request.onload = function() {
      play(request.response);
    }
    request.send();
  }

  loadSongWebAudioAPI('http://localhost:8282/loop.mp3');
}
window.addEventListener('load',init,false);

代码中的问题是，您正在复制MP3文件的另一个副本并将其附加到其末尾。该副本被解码器有效地忽略了-它不是原始缓冲区数据，它只是文件流中随机的虚假垃圾，后面是一个完美完整的MP3文件。

您需要做的是首先将音频数据解码到AudioBuffer中，然后将音频缓冲区附加到一个新的AudioBuffer中。这需要对代码进行一些重构。

你要做的是:

var context = new webkitAudioContext();
function init() {
  /**
   * Appends two ArrayBuffers into a new one.
   * 
   * @param {ArrayBuffer} buffer1 The first buffer.
   * @param {ArrayBuffer} buffer2 The second buffer.
   */
  function appendBuffer(buffer1, buffer2) {
    var numberOfChannels = Math.min( buffer1.numberOfChannels, buffer2.numberOfChannels );
    var tmp = context.createBuffer( numberOfChannels, (buffer1.length + buffer2.length), buffer1.sampleRate );
    for (var i=0; i<numberOfChannels; i++) {
      var channel = tmp.getChannelData(i);
      channel.set( buffer1.getChannelData(i), 0);
      channel.set( buffer2.getChannelData(i), buffer1.length);
    }
    return tmp;
  }
  /**
   * Loads a song
   * 
   * @param {String} url The url of the song.
   */
  function loadSongWebAudioAPI(url) {
    var request = new XMLHttpRequest();
    request.open('GET', url, true);
    request.responseType = 'arraybuffer';
    /**
     * Appends two ArrayBuffers into a new one.
     * 
     * @param {ArrayBuffer} data The ArrayBuffer that was loaded.
     */
    function play(data) {
      //decode the loaded data
      context.decodeAudioData(data, function(buf) {
        var audioSource = context.createBufferSource();
        audioSource.connect(context.destination);
        // Concatenate the two buffers into one.
        audioSource.buffer = appendBuffer(buf, buf);
        audioSource.noteOn(0);
        audioSource.playbackRate.value = 1;
      });
    };
    // When the song is loaded asynchronously try to play it.
    request.onload = function() {
      play(request.response);
    }
    request.send();
  }

  loadSongWebAudioAPI('loop.mp3');
}
window.addEventListener('load',init,false);

有一个轻微的播放间隙-这是因为你在声音样本开始时有近50ms的沉默，而不是由于循环问题。

希望这对你有帮助!

如果您需要从数组(不仅仅是2)中追加/连接缓冲区列表，这里有一个解决方案。我刚刚调整了一点@Cwilso代码(感谢您的帮助;)

function concatBuffer(_buffers) {
    // _buffers[] is an array containig our audiobuffer list
    var buflengh = _buffers.length;
    var channels = [];
    var totalDuration = 0;
    for(var a=0; a<buflengh; a++){
        channels.push(_buffers[a].numberOfChannels);// Store all number of channels to choose the lowest one after
        totalDuration += _buffers[a].duration;// Get the total duration of the new buffer when every buffer will be added/concatenated
    }
    var numberOfChannels = channels.reduce(function(a, b) { return Math.min(a, b); });;// The lowest value contained in the array channels
    var tmp = context.createBuffer(numberOfChannels, context.sampleRate * totalDuration, context.sampleRate);// Create new buffer
    for (var b=0; b<numberOfChannels; b++) {
        var channel = tmp.getChannelData(b);
        var dataIndex = 0;
        for(var c = 0; c < buflengh; c++) {
            channel.set(_buffers[c].getChannelData(b), dataIndex);
            dataIndex+=_buffers[c].length;// Next position where we should store the next buffer values
        }
    }
    return tmp;
}
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