HTML5录音实践总结(Preact)

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获取 PCM 数据

处理 PCM 数据

Float32 转 Int16

ArrayBuffer 转 Base64

PCM 文件播放

重采样

PCM 转 MP3

PCM 转 WAV

短时能量计算

Web Worker优化性能

音频存储(IndexedDB)

WebView 开启 WebRTC

获取 PCM 数据

查看 DEMO

https://github.com/deepkolos/pc-pcm-wave

样例代码:

const mediaStream = await window.navigator.mediaDevices.getUserMedia({    audio: {// sampleRate: 44100, // 采样率 不生效需要手动重采样        channelCount: 1, // 声道        // echoCancellation: true,        // noiseSuppression: true, // 降噪 实测效果不错    },})const audioContext = new window.AudioContext()const inputSampleRate = audioContext.sampleRateconst mediaNode = audioContext.createMediaStreamSource(mediaStream)if (!audioContext.createScriptProcessor) {audioContext.createScriptProcessor = audioContext.createJavaScriptNode}// 创建一个jsNodeconst jsNode = audioContext.createScriptProcessor(4096, 1, 1)jsNode.connect(audioContext.destination)jsNode.onaudioprocess = (e) => {    // e.inputBuffer.getChannelData(0) (left)    // 双通道通过e.inputBuffer.getChannelData(1)获取 (right)}mediaNode.connect(jsNode)

简要流程如下:

start=>start: 开始getUserMedia=>operation: 获取MediaStreamaudioContext=>operation: 创建AudioContextscriptNode=>operation: 创建scriptNode并关联AudioContextonaudioprocess=>operation: 设置onaudioprocess并处理数据end=>end: 结束start->getUserMedia->audioContext->scriptNode->onaudioprocess->end

停止录制只需要把 audioContext 挂在的 node 卸载即可,然后把存储的每一帧数据合并即可产出 PCM 数据

jsNode.disconnect()mediaNode.disconnect()jsNode.onaudioprocess = null

PCM 数据处理

通过 WebRTC 获取的 PCM 数据格式是 Float32 的, 如果是双通道录音的话, 还需要增加合并通道

const leftDataList = [];const rightDataList = [];function onAudioProcess(event) {  // 一帧的音频PCM数据  let audioBuffer = event.inputBuffer;  leftDataList.push(audioBuffer.getChannelData(0).slice(0));  rightDataList.push(audioBuffer.getChannelData(1).slice(0));}// 交叉合并左右声道的数据function 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;}

Float32 转 Int16

const float32 = new Float32Array(1)const int16 = Int16Array.from(float32.map(x => (x > 0 ? x * 0x7fff : x * 0x8000)),)

arrayBuffer 转 Base64

注意: 在浏览器上有个 btoa() 函数也是可以转换为 Base64 但是输入参数必须为字符串, 如果传递 buffer 参数会先被 toString() 然后再 Base64 , 使用 ffplay 播放反序列化的 Base64 , 会比较刺耳

使用 base64-arraybuffer 即可完成

import { encode } from 'base64-arraybuffer'const float32 = new Float32Array(1)const int16 = Int16Array.from(float32.map(x => (x > 0 ? x * 0x7fff : x * 0x8000)),)console.log(encode(int16.buffer))

验证 Base64 是否正确, 可以在 node 下把产出的 Base64 转换为 Int16 的 PCM 文件, 然后使用 FFPlay 播放, 看看音频是否正常播放

PCM 文件播放

# 单通道 采样率:16000 Int16ffplay -f s16le -ar 16k -ac 1 test.pcm# 双通道 采样率:48000 Float32ffplay -f f32le -ar 48000 -ac 2 test.pcm

重采样/调整采样率

虽然 getUserMedia 参数可设置采样率, 但是在最新Chrome也不生效, 所以需要手动做个重采样

const mediaStream = await window.navigator.mediaDevices.getUserMedia({    audio: {    // sampleRate: 44100, // 采样率 设置不生效        channelCount: 1, // 声道        // echoCancellation: true, // 减低回音        // noiseSuppression: true, // 降噪, 实测效果不错    },})

使用 wave-resampler 即可完成

import { resample } from 'wave-resampler'const inputSampleRate =  44100const outputSampleRate = 16000const resampledBuffers = resample(    // 需要onAudioProcess每一帧的buffer合并后的数组mergeArray(audioBuffers),inputSampleRate,outputSampleRate,)

PCM 转 MP3

import { Mp3Encoder } from 'lamejs'let mp3bufconst mp3Data = []const sampleBlockSize = 576 * 10 // 工作缓存区, 576的倍数const mp3Encoder = new Mp3Encoder(1, outputSampleRate, kbps)const samples = float32ToInt16(  audioBuffers,  inputSampleRate,  outputSampleRate,)let remaining = samples.lengthfor (let i = 0; remaining >= 0; i += sampleBlockSize) {  const left = samples.subarray(i, i + sampleBlockSize)  mp3buf = mp3Encoder.encodeBuffer(left)  mp3Data.push(new Int8Array(mp3buf))  remaining -= sampleBlockSize}mp3Data.push(new Int8Array(mp3Encoder.flush()))console.log(mp3Data)// 工具函数function float32ToInt16(audioBuffers, inputSampleRate, outputSampleRate) {  const float32 = resample(    // 需要onAudioProcess每一帧的buffer合并后的数组    mergeArray(audioBuffers),    inputSampleRate,    outputSampleRate,  )  const int16 = Int16Array.from(    float32.map(x => (x > 0 ? x * 0x7fff : x * 0x8000)),  )  return int16}

使用 lamejs 即可, 但是体积较大(160+KB), 如果没有存储需求可使用 WAV 格式

> ls -alh-rwxrwxrwx 1 root root  95K  4月 22 12:45 12s.mp3*-rwxrwxrwx 1 root root 1.1M  4月 22 12:44 12s.wav*-rwxrwxrwx 1 root root 235K  4月 22 12:41 30s.mp3*-rwxrwxrwx 1 root root 2.6M  4月 22 12:40 30s.wav*-rwxrwxrwx 1 root root  63K  4月 22 12:49 8s.mp3*-rwxrwxrwx 1 root root 689K  4月 22 12:48 8s.wav*

PCM 转 WAV

function mergeArray(list) {  const length = list.length * list[0].length  const 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}function writeUTFBytes(view, offset, string) {  var lng = string.length  for (let i = 0; i < lng; i++) {    view.setUint8(offset + i, string.charCodeAt(i))  }}function createWavBuffer(audioData, sampleRate = 44100, channels = 1) {  const WAV_HEAD_SIZE = 44  const buffer = new ArrayBuffer(audioData.length * 2 + WAV_HEAD_SIZE)  // 需要用一个view来操控buffer  const view = new DataView(buffer)  // 写入wav头部信息  // RIFF chunk descriptor/identifier  writeUTFBytes(view, 0, 'RIFF')  // RIFF chunk length  view.setUint32(4, 44 + audioData.length * 2, true)  // RIFF type  writeUTFBytes(view, 8, 'WAVE')  // format chunk identifier  // FMT sub-chunk  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, channels, 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, channels * 2, true)  // bits per sample  view.setUint16(34, 16, true)  // data sub-chunk  // data chunk identifier  writeUTFBytes(view, 36, 'data')  // data chunk length  view.setUint32(40, audioData.length * 2, true)  // 写入PCM数据  let index = 44  const volume = 1  const { length } = audioData  for (let i = 0; i < length; i++) {    view.setInt16(index, audioData[i] * (0x7fff * volume), true)    index += 2  }  return buffer}// 需要onAudioProcess每一帧的buffer合并后的数组createWavBuffer(mergeArray(audioBuffers))

WAV 基本上是 PCM 加上一些音频信息

简单的短时能量计算

function shortTimeEnergy(audioData) {  let sum = 0  const energy = []  const { length } = audioData  for (let i = 0; i < length; i++) {    sum += audioData[i] ** 2    if ((i + 1) % 256 === 0) {      energy.push(sum)      sum = 0    } else if (i === length - 1) {      energy.push(sum)    }  }  return energy}

由于计算结果有会因设备的录音增益差异较大, 计算出数据也较大, 所以使用比值简单区分人声和噪音

查看 DEMO

const NoiseVoiceWatershedWave = 2.3const energy = shortTimeEnergy(e.inputBuffer.getChannelData(0).slice(0))const avg = energy.reduce((a, b) => a + b) / energy.lengthconst nextState = Math.max(...energy) / avg > NoiseVoiceWatershedWave ? 'voice' : 'noise'

Web Worker 优化性能

音频数据数据量较大, 所以可以使用 Web Worker 进行优化, 不卡 UI 线程

在 Webpack 项目里 Web Worker 比较简单, 安装 worker-loader 即可

preact.config.js

export default (config, env, helpers) => {    config.module.rules.push({        test: /\.worker\.js$/,        use: { loader: 'worker-loader', options: { inline: true } },      })}

recorder.worker.js

self.addEventListener('message', event => {  console.log(event.data)  // 转MP3/转Base64/转WAV等等  const output = ''  self.postMessage(output)}

使用 Worker

async function toMP3(audioBuffers, inputSampleRate, outputSampleRate = 16000) {  const { default: Worker } = await import('./recorder.worker')  const worker = new Worker()  // 简单使用, 项目可以在recorder实例化的时候创建worker实例, 有并法需求可多个实例  return new Promise(resolve => {    worker.postMessage({      audioBuffers: audioBuffers,      inputSampleRate: inputSampleRate,      outputSampleRate: outputSampleRate,      type: 'mp3',    })    worker.onmessage = event => resolve(event.data)  })}

音频的存储

浏览器持久化储存的地方有 LocalStorage 和 IndexedDB , 其中 LocalStorage 较为常用, 但是只能储存字符串, 而 IndexedDB 可直接储存 Blob , 所以优先选择 IndexedDB ,使用 LocalStorage 则需要转 Base64 体积将会更大

所以为了避免占用用户太多空间, 所以选择MP3格式进行存储

> ls -alh-rwxrwxrwx 1 root root  95K  4月 22 12:45 12s.mp3*-rwxrwxrwx 1 root root 1.1M  4月 22 12:44 12s.wav*-rwxrwxrwx 1 root root 235K  4月 22 12:41 30s.mp3*-rwxrwxrwx 1 root root 2.6M  4月 22 12:40 30s.wav*-rwxrwxrwx 1 root root  63K  4月 22 12:49 8s.mp3*-rwxrwxrwx 1 root root 689K  4月 22 12:48 8s.wav*

IndexedDB 简单封装如下, 熟悉后台的同学可以找个 ORM 库方便数据读写

const indexedDB =  window.indexedDB ||  window.webkitIndexedDB ||  window.mozIndexedDB ||  window.OIndexedDB ||  window.msIndexedDBconst IDBTransaction =  window.IDBTransaction ||  window.webkitIDBTransaction ||  window.OIDBTransaction ||  window.msIDBTransactionconst readWriteMode =  typeof IDBTransaction.READ_WRITE === 'undefined'    ? 'readwrite'    : IDBTransaction.READ_WRITEconst dbVersion = 1const storeDefault = 'mp3'let dbLinkfunction initDB(store) {  return new Promise((resolve, reject) => {    if (dbLink) resolve(dbLink)    // Create/open database    const request = indexedDB.open('audio', dbVersion)    request.onsuccess = event => {      const db = request.result      db.onerror = event => {        reject(event)      }      if (db.version === dbVersion) resolve(db)    }    request.onerror = event => {      reject(event)    }    // For future use. Currently only in latest Firefox versions    request.onupgradeneeded = event => {      dbLink = event.target.result      const { transaction } = event.target      if (!dbLink.objectStoreNames.contains(store)) {        dbLink.createObjectStore(store)      }      transaction.oncomplete = event => {        // Now store is available to be populated        resolve(dbLink)      }    }  })}export const writeIDB = async (name, blob, store = storeDefault) => {  const db = await initDB(store)  const transaction = db.transaction([store], readWriteMode)  const objStore = transaction.objectStore(store)  return new Promise((resolve, reject) => {    const request = objStore.put(blob, name)    request.onsuccess = event => resolve(event)    request.onerror = event => reject(event)    transaction.commit && transaction.commit()  })}export const readIDB = async (name, store = storeDefault) => {  const db = await initDB(store)  const transaction = db.transaction([store], readWriteMode)  const objStore = transaction.objectStore(store)  return new Promise((resolve, reject) => {    const request = objStore.get(name)    request.onsuccess = event => resolve(event.target.result)    request.onerror = event => reject(event)    transaction.commit && transaction.commit()  })}export const clearIDB = async (store = storeDefault) => {  const db = await initDB(store)  const transaction = db.transaction([store], readWriteMode)  const objStore = transaction.objectStore(store)  return new Promise((resolve, reject) => {    const request = objStore.clear()    request.onsuccess = event => resolve(event)    request.onerror = event => reject(event)    transaction.commit && transaction.commit()  })}

WebView 开启 WebRTC

见 WebView WebRTC not working

webView.setWebChromeClient(new WebChromeClient(){@TargetApi(Build.VERSION_CODES.LOLLIPOP)@Overridepublic void onPermissionRequest(final PermissionRequest request) {request.grant(request.getResources());}});

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