问题
The other day I stumbled upon with this example of a Javascript audio recorder:
http://webaudiodemos.appspot.com/AudioRecorder/index.html
Which I ended up using for implementing my own. The problem I'm having is that in this file:
var audioContext = new webkitAudioContext();
var audioInput = null,
realAudioInput = null,
inputPoint = null,
audioRecorder = null;
var rafID = null;
var analyserContext = null;
var canvasWidth, canvasHeight;
var recIndex = 0;
/* TODO:
- offer mono option
- "Monitor input" switch
*/
function saveAudio() {
audioRecorder.exportWAV( doneEncoding );
}
function drawWave( buffers ) {
var canvas = document.getElementById( "wavedisplay" );
drawBuffer( canvas.width, canvas.height, canvas.getContext('2d'), buffers[0] );
}
function doneEncoding( blob ) {
Recorder.forceDownload( blob, "myRecording" + ((recIndex<10)?"0":"") + recIndex + ".wav" );
recIndex++;
}
function toggleRecording( e ) {
if (e.classList.contains("recording")) {
// stop recording
audioRecorder.stop();
e.classList.remove("recording");
audioRecorder.getBuffers( drawWave );
} else {
// start recording
if (!audioRecorder)
return;
e.classList.add("recording");
audioRecorder.clear();
audioRecorder.record();
}
}
// this is a helper function to force mono for some interfaces that return a stereo channel for a mono source.
// it's not currently used, but probably will be in the future.
function convertToMono( input ) {
var splitter = audioContext.createChannelSplitter(2);
var merger = audioContext.createChannelMerger(2);
input.connect( splitter );
splitter.connect( merger, 0, 0 );
splitter.connect( merger, 0, 1 );
return merger;
}
function toggleMono() {
if (audioInput != realAudioInput) {
audioInput.disconnect();
realAudioInput.disconnect();
audioInput = realAudioInput;
} else {
realAudioInput.disconnect();
audioInput = convertToMono( realAudioInput );
}
audioInput.connect(inputPoint);
}
function cancelAnalyserUpdates() {
window.webkitCancelAnimationFrame( rafID );
rafID = null;
}
function updateAnalysers(time) {
if (!analyserContext) {
var canvas = document.getElementById("analyser");
canvasWidth = canvas.width;
canvasHeight = canvas.height;
analyserContext = canvas.getContext('2d');
}
// analyzer draw code here
{
var SPACING = 3;
var BAR_WIDTH = 1;
var numBars = Math.round(canvasWidth / SPACING);
var freqByteData = new Uint8Array(analyserNode.frequencyBinCount);
analyserNode.getByteFrequencyData(freqByteData);
analyserContext.clearRect(0, 0, canvasWidth, canvasHeight);
analyserContext.fillStyle = '#F6D565';
analyserContext.lineCap = 'round';
var multiplier = analyserNode.frequencyBinCount / numBars;
// Draw rectangle for each frequency bin.
for (var i = 0; i < numBars; ++i) {
var magnitude = 0;
var offset = Math.floor( i * multiplier );
// gotta sum/average the block, or we miss narrow-bandwidth spikes
for (var j = 0; j< multiplier; j++)
magnitude += freqByteData[offset + j];
magnitude = magnitude / multiplier;
var magnitude2 = freqByteData[i * multiplier];
analyserContext.fillStyle = "hsl( " + Math.round((i*360)/numBars) + ", 100%, 50%)";
analyserContext.fillRect(i * SPACING, canvasHeight, BAR_WIDTH, -magnitude);
}
}
rafID = window.webkitRequestAnimationFrame( updateAnalysers );
}
function gotStream(stream) {
// "inputPoint" is the node to connect your output recording to.
inputPoint = audioContext.createGainNode();
// Create an AudioNode from the stream.
realAudioInput = audioContext.createMediaStreamSource(stream);
audioInput = realAudioInput;
audioInput.connect(inputPoint);
// audioInput = convertToMono( input );
analyserNode = audioContext.createAnalyser();
analyserNode.fftSize = 2048;
inputPoint.connect( analyserNode );
audioRecorder = new Recorder( inputPoint );
zeroGain = audioContext.createGainNode();
zeroGain.gain.value = 0.0;
inputPoint.connect( zeroGain );
zeroGain.connect( audioContext.destination );
updateAnalysers();
}
function initAudio() {
if (!navigator.webkitGetUserMedia)
return(alert("Error: getUserMedia not supported!"));
navigator.webkitGetUserMedia({audio:true}, gotStream, function(e) {
alert('Error getting audio');
console.log(e);
});
}
window.addEventListener('load', initAudio );
As you might be able to see, the initAudio() function (the one wich ask the user for permission to use his/her microphone) is called inmediately when the page is loaded (read the last line) with this method:
window.addEventListener('load', initAudio );
Now, I have this code in the HTML:
<script type="text/javascript" >
$(function() {
$("#recbutton").on("click", function() {
$("#entrance").hide();
$("#live").fadeIn("slow");
toggleRecording(this);
$(this).toggle();
return $("#stopbutton").toggle();
});
return $("#stopbutton").on("click", function() {
audioRecorder.stop();
$(this).toggle();
$("#recbutton").toggle();
$("#live").hide();
return $("#entrance").fadeIn("slow");
});
});
</script>
And as you can see, I call the toggleRecording(this) function (the one wich starts the recording process) only after the #recbutton is pressed. Now, everything works fine with this code BUT, the user gets prompted for microphone permission as soon as the page is loaded and I want to ask them for permission to use the microphone ONLY AFTER they clicked the #recbutton Do you understand me? I tought that if I remove the last line of the first file:
window.addEventListener('load', initAudio );
and modify my embedded script like this:
<script type="text/javascript" >
$(function() {
$("#recbutton").on("click", function() {
$("#entrance").hide();
$("#live").fadeIn("slow");
initAudio();
toggleRecording(this);
$(this).toggle();
return $("#stopbutton").toggle();
});
return $("#stopbutton").on("click", function() {
audioRecorder.stop();
$(this).toggle();
$("#recbutton").toggle();
$("#live").hide();
return $("#entrance").fadeIn("slow");
});
});
</script>
I might be able to achieve what I wanted, and actually I am, the user doesn't get prompted for his/her microphone until they click the #recbutton. The problem is, the audio never get's recorded, when you try to download it, the resulting WAV it is empty.
How can I fix this?
My project's code is at: https://github.com/Jmlevick/html-recorder
回答1:
No, your problem is that getUserMedia() has an asynchronous callback (gotMedia()); you need to have the rest of your code logic in the startbutton call (the toggleRecording bit, in particular) inside that callback, because right now it's getting executed before getUserMedia returns (and sets up the audio nodes).
回答2:
I found an elegant & easy solution for this (or at least I see it that way):
What I did was toss "main.js" and "recorder.js" inside a getScript call that is executed only when a certain button (#button1) is clicked by the user... These scripts do not get loaded with the webpage itself until the button it's pressed, but we need some more nifty tricks to make it work the way I described and wanted above:
in main.js, I changed:
window.addEventListener('load', initAudio );
for:
window.addEventListener('click', initAudio );
So when the scripts are loaded into the page with getScript the "main.js" file now listens for a click event in the webpage to ask the user for the microphone. Next, I had to create a hidden button (#button2) on the page wich is fakely clicked by jQuery exactly right after the scripts are loaded on the page, so it triggers the "ask for microphone permisson" event and then, just below that line of code wich generates the fake click I added:
window.removeEventListener("click", initAudio, false);
so the "workflow" for this trick ends up as follows:
User presses a button wich loads the necesary js files into the page with getScript, it's worth mentioning that now the "main.js" file listens for a click event on the window instead of a load one.
We have a hidden button wich is "fakely clicked" by jQuery just in the moment you click the first one, so it triggers the permisson event for the user.
Once this event is triggered, the click event listener is removed from the window, so it never fires the "ask for permisson" event again when the user clicks anywhere on the page.
And basically that's all folks! :) now when the user goes into the page he/she never get asked for microphone permisson until they click a "Rec" button on the page just as I wanted. With one click of the user we do 3 things in jQuery, but for the user it seems like nothing happened other that the "microphone permisson message" appearing on the screen instantly right after they click the "Rec" Button.
来源：https://stackoverflow.com/questions/17123263/ask-for-microphone-on-onclick-event