Web RTC + audio API 实现录音，并压缩

    <button onclick="record()">开始录音</button>
    <button onclick="stopRecord()">结束录音</button>
    <!-- <button onclick="resetRecord()">重置录音</button> -->
    <audio class="audio-node" id="audio" autoplay></audio>
    <script>
 class Recoder {
  constructor (sampleRate) {
    this.leftDataList = []
    this.rightDataList = []
    this.mediaPlayer = null
    this.audioContext = null
    this.source = null
    this.sampleRate = sampleRate || 44100
  }
  startRecord () {
    return new Promise((resolve, reject) => {
      window.navigator.mediaDevices.getUserMedia({
        audio: {
          sampleRate: 8000, // 采样率
          channelCount: 1, // 声道
          audioBitsPerSecond : 64,
          volume: 1.0, // 音量
          autoGainControl: true
        }
      }).then(mediaStream => {
        console.log(mediaStream,‘mediaStream‘)
        this.mediaPlayer = mediaStream
        this.beginRecord(mediaStream)
        resolve()
      }).catch(err => {
        // 如果用户电脑没有麦克风设备或者用户拒绝了，或者连接出问题了等
        // 这里都会抛异常，并且通过err.name可以知道是哪种类型的错误
        console.error(err)
        reject(err)
      })
    })
  }

  beginRecord (mediaStream) {
    let audioContext = new (window.AudioContext || window.webkitAudioContext)()
    // mediaNode包含 mediaStream，audioContext
    let mediaNode = audioContext.createMediaStreamSource(mediaStream)
    console.log(mediaNode,‘mediaNode‘)
    // 创建一个jsNode
    // audioContext.sampleRate = 8000
    console.log(audioContext,‘audioContext‘)
    let jsNode = this.createJSNode(audioContext)
    console.log(jsNode,‘jsnode‘)
    // 需要连到扬声器消费掉outputBuffer，process回调才能触发
    // 并且由于不给outputBuffer设置内容，所以扬声器不会播放出声音
    jsNode.connect(audioContext.destination)
    jsNode.onaudioprocess = this.onAudioProcess.bind(this)
    // 把mediaNode连接到jsNode
    mediaNode.connect(jsNode)
    this.audioContext = audioContext
  }

  onAudioProcess (event) {
    console.log(‘is recording‘)
    // 拿到输入buffer Float32Array 
    let audioBuffer = event.inputBuffer
    let leftChannelData = audioBuffer.getChannelData(0)
   // let rightChannelData = audioBuffer.getChannelData(1)
 
    // 需要克隆一下
    this.leftDataList.push(leftChannelData.slice(0))
    //this.rightDataList.push(rightChannelData.slice(0))
  }

  createJSNode (audioContext) {
    const BUFFER_SIZE = 4096
    const INPUT_CHANNEL_COUNT = 1
    const OUTPUT_CHANNEL_COUNT = 1
    // createJavaScriptNode已被废弃
    let creator = audioContext.createScriptProcessor || audioContext.createJavaScriptNode
    creator = creator.bind(audioContext)
    return creator(BUFFER_SIZE, INPUT_CHANNEL_COUNT, OUTPUT_CHANNEL_COUNT)
  }

  playRecord (arrayBuffer) {
    let blob = new Blob([new Int8Array(arrayBuffer)], {
      type: ‘audio/mp3‘ // files[0].type
    })
    let blobUrl = URL.createObjectURL(blob)
    this.source = blob
    this.blobUrl = blobUrl
    // document.querySelector(‘.audio-node‘).src = blobUrl
    return blobUrl
  }

  stopRecord () {
    // 停止录音
    let leftData = this.mergeArray(this.leftDataList)
    //let rightData = this.mergeArray(this.rightDataList)
    let allData = this.interSingleData(leftData)
    let wavBuffer = this.createWavFile(allData)

    let source = this.playRecord(wavBuffer)
    this.resetRecord()
    return source
  }

  transformArrayBufferToBase64 (buffer) {
    var binary = ‘‘
    var bytes = new Uint8Array(buffer)
    for (var len = bytes.byteLength, i = 0; i < len; i++) {
      binary += String.fromCharCode(bytes[i])
    }
    return window.btoa(binary)
  }

  // 停止控件录音
  resetRecord () {
    this.leftDataList = []
    this.rightDataList = []
    this.audioContext.close()
    this.mediaPlayer.getAudioTracks().forEach(track => {
      track.stop()
      this.mediaPlayer.removeTrack(track)
    })
  }

  createWavFile (audioData) {
    let channelCount = 1
    const WAV_HEAD_SIZE = 44
    const sampleBits = 16
    let sampleRate = this.sampleRate

    let buffer = new ArrayBuffer(audioData.length * 2 + WAV_HEAD_SIZE)
    // 需要用一个view来操控buffer
    let view = new DataView(buffer)
    // 写入wav头部信息
    // RIFF chunk descriptor/identifier
    this.writeUTFBytes(view, 0, ‘RIFF‘)
    // RIFF chunk length
    view.setUint32(4, 44 + audioData.length * channelCount, true)
    // RIFF type
    this.writeUTFBytes(view, 8, ‘WAVE‘)
    // format chunk identifier
    // FMT sub-chunk
    this.writeUTFBytes(view, 12, ‘fmt ‘)
    // format chunk length
    view.setUint32(16, 16, true)
    // sample format (raw)
    view.setUint16(20, 1, true)
    // stereo (2 channels)
    view.setUint16(22, channelCount, true)
    // sample rate
    view.setUint32(24, sampleRate , true)
    // byte rate (sample rate * block align)
    view.setUint32(28, sampleRate * 2, true)
    // block align (channel count * bytes per sample)
    view.setUint16(32, 2 * 2, true)
    // bits per sample
    view.setUint16(34, 16, true)
    // data sub-chunk
    // data chunk identifier
    this.writeUTFBytes(view, 36, ‘data‘)
    // data chunk length
    view.setUint32(40, audioData.length * 2, true)

    console.log(view,‘view‘)
    let length = audioData.length
    let index = 44
    let volume = 1
    for (let i = 0; i < length; i++) {
      view.setInt16(index, audioData[i] * (0x7FFF * volume), true)
      index += 2
    }
    return buffer
  }

  writeUTFBytes (view, offset, string) {
    var lng = string.length
    for (var i = 0; i < lng; i++) {
      view.setUint8(offset + i, string.charCodeAt(i))
    }
  }

  interSingleData (left) {
      var t = left.length;
      let sampleRate = this.audioContext.sampleRate,
      outputSampleRate = this.sampleRate
      sampleRate += 0.0;
      outputSampleRate += 0.0;
      var s = 0,
      o = sampleRate / outputSampleRate,
      u = Math.ceil(t * outputSampleRate / sampleRate),
      a = new Float32Array(u);
      for (let i = 0; i < u; i++) {
        a[i] = left[Math.floor(s)];
        s += o;
      }
      return a;
  }

  // 交叉合并左右声道的数据
  interleaveLeftAndRight (left, right) {
    let totalLength = left.length + right.length
    let data = new Float32Array(totalLength)
    for (let i = 0; i < left.length; i++) {
      let k = i * 2
      data[k] = left[i]
      data[k + 1] = right[i]
    }
    return data
  }

  mergeArray (list) {
    let length = list.length * list[0].length
    let data = new Float32Array(length)
    let offset = 0
    for (let i = 0; i < list.length; i++) {
      data.set(list[i], offset)
      offset += list[i].length
    }
    return data
  }

  // 播放音乐
  playMusic () {
    if (!this.value) {
      return
    }
    // 直接使用File对象生成blob url
    let blobUrl = URL.createObjectURL(this.files[0])
    document.querySelector(‘.audio-node‘).src = blobUrl
  }

  play (arrayBuffer) {
    // Safari需要使用webkit前缀
    let AudioContext = this.AudioContext || this.webkitAudioContext
    let audioContext = new AudioContext()
    // 创建一个AudioBufferSourceNode对象，使用AudioContext的工厂函数创建
    let audioNode = audioContext.createBufferSource()
    // 解码音频，可以使用Promise，但是较老的Safari需要使用回调
    audioContext.decodeAudioData(arrayBuffer, function (audioBuffer) {
      audioNode.buffer = audioBuffer
      audioNode.connect(audioContext.destination)
      // 从0s开始播放
      audioNode.start(0)
    })
  }
}
let recoder = new Recoder(8000)
function record() {
  recoder.startRecord()
}

function stopRecord(params) {
    recoder.stopRecord()
    let source = recoder.source
    let formData = new FormData()
    formData.append(‘audio‘, source)
    let audio = document.getElementById(‘audio‘)
    audio.src = recoder.blobUrl
}
</script>