一般录音都是通过麦克风来录制的，如果要录电脑自己播放的声音，我们可以通过js中分享屏幕音频来获取电脑扬声器播放的声音，代码如下：
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>MP3 Recorder</title>
<script type="text/javascript" src="//repo.bfw.wiki/bfwrepo/js/sprintf.min.js"></script>
<script type="text/javascript" src="//repo.bfw.wiki/bfwrepo/js/lame.all.js"></script>
</head>
<body>
<p>本工具可以录制在线视频的音乐（电脑声卡播放的声音），直接浏览器生成，数据不会传服务器</p>
<p>操作步骤：点击power，选择分享整个屏幕或者对应标签页(没有影响)，勾选分享音频，然后点击start即可开始录制，点击stop结束录制，按文件名下载</p>
<p>之后你可以修改文件名，然后上传到网易云音乐的云盘，这样你就可以在手机上听或者下载音乐了</p>
<audio id="AudioPlayer" controls="controls">
<source type="audio/mpeg">
</audio><br>
<button id="btnPower"BfwOnclick="onPower()">Power</button>
<button id="btnRecord"BfwOnclick="onRecord()" disabled="">Record</button>
<button id="btnStop"BfwOnclick="onStop()" disabled="">Stop</button>
<p>
<a id="DownloadLink" download="recorded.mp3">recorded.mp3</a>
<span id="status"></span>
</p>
<div id="log" style="width:100%; border:solid thin; margin:8px; padding:4px;">
Waiting for scripts...<br> Window loaded.<br>
</div>
<script id="logger" type="text/javascript">
//printf-style console output.
function log(fmt,args) {
var text= this.sprintf.apply(this,arguments);
var element= document.querySelector('#log');
element.innerHTML+= text+"<br>\n";
}
//printf-style status line.
function status(fmt,args) {
var text= this.sprintf.apply(this,arguments);
var element= document.getElementById('status');
element.innerHTML= text;
}
(function(window) {
log("Window loaded.");
})(window);
</script>
<script id="loadjs" type="text/javascript">
//Load a supplemental javascript on demand.
//cb is the function that will be called when the script is ready.
function loadScript(name,path,cb) {
var node= document.createElement('SCRIPT');
node.type= 'text/javascript';
node.src= path;
var head= document.getElementsByTagName('HEAD');
if(head[0]!=null)
head[0].appendChild(node);
if(cb!=null) {
node.onreadystagechange= cb;
node.onload= cb;
}
}
</script>
<script id="taskUI" type="text/javascript">
//(C)2016 nlited systems inc. http://nlited.org
var gAudio= null; //Audio context
var gAudioSrc= null; //Audio source
var gNode= null; //The audio processor node
var gIsLame= false; //Has lame.min.js been loaded?
var gLame= null; //The LAME encoder library
var gEncoder= null; //The MP3 encoder object
var gStrmMp3= []; //Collection of MP3 buffers
var gIsRecording= false;
var gCfg= { //Encoder configuration
chnlCt: 2, //1=mono, 2=stereo
bufSz: 4096, //input buffer size (bytes), 16bit signed int.
sampleRate: 44100,//Input sample rate (samples per second)
bitRate: 128 //Output bit rate (9-128)
};
var gPcmCt= 0; //Total input bytes
var gMp3Ct= 0; //Total output bytes
//Power button
function onPower(btn) {
if(!gAudio) {
PowerOn();
} else {
PowerOff();
}
}
async function startCapture() {
let captureStream = null;
try {
captureStream = await navigator.mediaDevices.getDisplayMedia({audio: { autoGainControl:false,echoCancellation:false,
googleAutoGainControl:false,noiseSuppression:false
} ,video: true});
} catch(err) {
console.error("Error: " + err);
}
return captureStream;
}
function PowerOn() {
log("Powering up...");
var caps= { audio: true };
try {
//Browser compatibility
window.AudioContext= window.AudioContext || window.webkitAudioContext || AudioContext;
navigator.getUserMedia= navigator.getUserMedia
|| navigator.webkitGetUserMedia
|| navigator.mozGetUserMedia
|| navigator.msGetUserMedia
|| MediaDevices.getUserMedia;
//test
if(!(gAudio= new window.AudioContext())) {
log("ERR: Unable to create AudioContext.");
} else {
// navigator.getUserMedia(caps,onUserMedia,onFail);
recorderStream=startCapture()
recorderStream.then(v =>{
audio_track = v.getAudioTracks()
audio_steam = new MediaStream(audio_track)
onUserMedia(audio_steam)}
)
}
} catch(ex) {
console.log(ex)
log("ERR: Unable to find any audio support.");
gAudio= null;
}
function onFail(ex) {
log("ERR: getUserMedia failed: %s",ex);
}
}
//Called when audio capture has been created.
function onUserMedia(stream) {
console.log(stream);
if(!(gAudioSrc= gAudio.createMediaStreamSource(stream))) {
log("ERR: Unable to create audio source.");
} else if(!gIsLame) {
log("Fetching encoder...");
// loadScript("lame","//repo.bfw.wiki/bfwrepo/js/lame.all.js",LameCreate);
LameCreate();
} else {
LameCreate();
}
}
//Called when the lame library has been loaded.
function LameCreate() {
gIsLame= true;
if(!(gEncoder= Mp3Create())) {
log("ERR: Unable to create MP3 encoder.");
} else {
gStrmMp3= [];
gPcmCt= 0;
gMp3Ct= 0;
log("Power ON.");
document.getElementById('btnRecord').disabled= false;
document.getElementById('btnStop').disabled= false;
}
}
//Create the mp3 encoder object.
function Mp3Create() {
if(!(gLame= new lamejs())) {
log("ERR: Unable to create LAME object.");
} else if(!(gEncoder= new lamejs.Mp3Encoder(gCfg.chnlCt,gCfg.sampleRate,gCfg.bitRate))) {
log("ERR: Unable to create MP3 encoder.");
} else {
log("MP3 encoder created.");
}
return(gEncoder);
}
//Shut everything down.
function PowerOff() {
log("Power down...");
if(gIsRecording) {
log("ERR: PowerOff: You need to stop recording first.");
} else {
gEncoder= null;
gLame= null;
gNode= null;
gAudioSrc= null;
gAudio= null;
log("Power OFF.");
document.getElementById('btnRecord').disabled= true;
document.getElementById('btnStop').disabled= true;
}
}
//Record button: Begin recording.
function onRecord(btn) {
var creator;
log("Start recording...");
if(!gAudio) {
log("ERR: No Audio source.");
} else if(!gEncoder) {
log("ERR: No encoder.");
} else if(gIsRecording) {
log("ERR: Already recording.");
} else {
//Create the audio capture node.
if(!gNode) {
if(!(creator= gAudioSrc.context.createScriptProcessor || gAudioSrc.createJavaScriptNode)) {
log("ERR: No processor creator?");
} else if(!(gNode= creator.call(gAudioSrc.context,gCfg.bufSz,gCfg.chnlCt,gCfg.chnlCt))) {
log("ERR: Unable to create processor node.");
}
}
if(!gNode) {
log("ERR: onRecord: No processor node.");
} else {
//Set callbacks, connect the node between the audio source and destination.
gNode.onaudioprocess= onAudioProcess;
gAudioSrc.connect(gNode);
gNode.connect(gAudioSrc.context.destination);
gIsRecording= true;
log("RECORD");
}
}
}
//Stop recording.
function onStop(btn) {
log("Stop recording...");
if(!gAudio) {
log("ERR: onStop: No audio.");
} else if(!gAudioSrc) {
log("ERR: onStop: No audio source.");
} else if(!gIsRecording) {
log("ERR: onStop: Not recording.");
} else {
//Disconnect the node
gNode.onaudioprocess= null;
gAudioSrc.disconnect(gNode);
gNode.disconnect();
gIsRecording= false;
//Flush the last mp3 buffer.
var mp3= gEncoder.flush();
if(mp3.length>0)
gStrmMp3.push(mp3);
//Present the mp3 stream on the page.
showMp3(gStrmMp3);
log("STOP");
}
}
//Process a single audio buffer.
//Input is an array of floating-point samples.
function onAudioProcess(e) {
//Cap output stream size
if(gMp3Ct > 10*1000*1000)
return;
var inBuf= e.inputBuffer;
var leftsamples= inBuf.getChannelData(0);
var rightsamples= inBuf.getChannelData(0);
var leftsampleCt= leftsamples.length;
var rightsampleCt= rightsamples.length;
//Convert floating-point to 16bit signed int.
//This may modify the number of samples.
var leftsamples16= convertFloatToInt16(leftsamples);
var rightsamples16= convertFloatToInt16(rightsamples);
if(leftsamples16.length > 0) {
gPcmCt+= leftsamples16.length*2;
gPcmCt+= rightsamples.length*2;
//Encode PCM to mp3
var mp3buf= gEncoder.encodeBuffer(leftsamples16,rightsamples16);
var mp3Ct= mp3buf.length;
if(mp3Ct>0) {
//Add buffer to in-memory output stream.
gStrmMp3.push(mp3buf);
gMp3Ct+= mp3Ct;
}
status("%d / %d: %2.2f%%",gPcmCt,gMp3Ct,(gMp3Ct*100)/gPcmCt);
}
}
//Convert floating point to 16bit signed int.
function convertFloatToInt16(inFloat) {
var sampleCt= inFloat.length;
var outInt16= new Int16Array(sampleCt);
for(var n1=0;n1<sampleCt;n1++) {
//This is where I can apply waveform modifiers.
var sample16= 0x8000*inFloat[n1];
//Clamp value to avoid integer overflow, which causes audible pops and clicks.
sample16= (sample16 < -32767) ? -32767 : (sample16 > 32767) ? 32767 : sample16;
outInt16[n1]= sample16;
}
return(outInt16);
}
//Present the output mp3 stream on the page
//as a download link and content in the audio control.
function showMp3(mp3) {
//Consolidate the collection of MP3 buffers into a single data Blob.
var blob= new Blob(gStrmMp3,{type: 'audio/mp3'});
//Create a URL to the blob.
var url= window.URL.createObjectURL(blob);
//Use the blob as the source for link and audio control
var audio= document.getElementById('AudioPlayer');
var download= document.getElementById('DownloadLink');
audio.src= url;
download.href= url;
}
</script>
</body>
</html>
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