前端播放pcm音频流

难点：pcm为音频裸数据流，无法直接像mp3。wav这样已经包装好的音频一样，直接使用audio等等一些网上的工具来播放，确实是麻烦。

代码(接收websocket传输过来的pcm音频流数据，需要后端告知采样率，通道，采样位数，pcm刷新间隔几个参数)

1.player-pcm.js文件

function PCMPlayer(option) {
    this.init(option);
}

PCMPlayer.prototype.init = function (option) {
    var defaults = {
        encoding: '16bitInt',//编码格式
        channels: 1,//声道
        sampleRate: 8000,//采样率
        flushingTime: 1000//pcm数据刷新间隔
    };
    this.option = Object.assign({}, defaults, option);
    this.samples = new Float32Array();
    this.flush = this.flush.bind(this);
    this.interval = setInterval(this.flush, this.option.flushingTime);
    this.maxValue = this.getMaxValue();
    this.typedArray = this.getTypedArray();
    this.createContext();
};

PCMPlayer.prototype.getMaxValue = function () {
    var encodings = {
        '8bitInt': 128,
        '16bitInt': 32768,
        '32bitInt': 2147483648,
        '32bitFloat': 1
    }

    return encodings[this.option.encoding] ? encodings[this.option.encoding] : encodings['16bitInt'];
};

PCMPlayer.prototype.getTypedArray = function () {
    var typedArrays = {
        '8bitInt': Int8Array,
        '16bitInt': Int16Array,
        '32bitInt': Int32Array,
        '32bitFloat': Float32Array
    }

    return typedArrays[this.option.encoding] ? typedArrays[this.option.encoding] : typedArrays['16bitInt'];
};

PCMPlayer.prototype.createContext = function () {
    this.audioCtx = new (window.AudioContext || window.webkitAudioContext)();
    this.gainNode = this.audioCtx.createGain();
    this.gainNode.gain.value = 1;
    this.gainNode.connect(this.audioCtx.destination);
    this.startTime = this.audioCtx.currentTime;
};

PCMPlayer.prototype.isTypedArray = function (data) {
    return (data.byteLength && data.buffer && data.buffer.constructor == ArrayBuffer);
};
// 播放原始pcm裸数据
PCMPlayer.prototype.feed = function (data) {
    if (!this.isTypedArray(data)) return;
    data = this.getFormatedValue(data);
    var tmp = new Float32Array(this.samples.length + data.length);
    tmp.set(this.samples, 0);
    tmp.set(data, this.samples.length);
    this.samples = tmp;
};
// 格式化
PCMPlayer.prototype.getFormatedValue = function (data) {
    var data = new this.typedArray(data.buffer),
        float32 = new Float32Array(data.length),
        i;

    for (i = 0; i < data.length; i++) {
        float32[i] = data[i] / this.maxValue;
    }
    return float32;
};
// 控制播放器音量
PCMPlayer.prototype.volume = function (volume) {
    this.gainNode.gain.value = volume;
};
// 销毁播放器实例
PCMPlayer.prototype.destroy = function () {
    if (this.interval) {
        clearInterval(this.interval);
    }
    this.samples = null;
    this.audioCtx.close();
    this.audioCtx = null;
};

PCMPlayer.prototype.flush = function () {
    if (!this.samples.length) return;
    var bufferSource = this.audioCtx.createBufferSource(),
        length = this.samples.length / this.option.channels,
        audioBuffer = this.audioCtx.createBuffer(this.option.channels, length, this.option.sampleRate),
        audioData,
        channel,
        offset,
        i,
        decrement;

    for (channel = 0; channel < this.option.channels; channel++) {
        audioData = audioBuffer.getChannelData(channel);
        offset = channel;
        decrement = 50;
        for (i = 0; i < length; i++) {
            audioData[i] = this.samples[offset];
            /* fadein */
            if (i < 50) {
                audioData[i] = (audioData[i] * i) / 50;
            }
            /* fadeout*/
            if (i >= (length - 51)) {
                audioData[i] = (audioData[i] * decrement--) / 50;
            }
            offset += this.option.channels;
        }
    }

    if (this.startTime < this.audioCtx.currentTime) {
        this.startTime = this.audioCtx.currentTime;
    }
    console.log('start vs current ' + this.startTime + ' vs ' + this.audioCtx.currentTime + ' duration: ' + audioBuffer.duration);
    bufferSource.buffer = audioBuffer;
    bufferSource.connect(this.gainNode);
    bufferSource.start(this.startTime);
    this.startTime += audioBuffer.duration;
    this.samples = new Float32Array();
};


export default PCMPlayer

2.使用

//创建实例
 var player = new PCMPlayer({
      encoding: "16bitInt",
      channels: 2,
      sampleRate: 8000,
      flushingTime: 2000
    });
//接收到数据播放音频（event为接收到的pcm数据）
var data = new Uint8Array(event.data);
   player.feed(data);