在 onclick 事件上请求麦克风

有一天，我偶然发现了这个 Javascript 录音机的例子：

http://webaudiodemos.appspot.com/AudioRecorder/index.html http://webaudiodemos.appspot.com/AudioRecorder/index.html

我最终用它来实现我自己的。我遇到的问题是在这个文件中：

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 );

正如您可能看到的，初始化音频()当页面加载（阅读最后一行）时，使用以下方法立即调用函数（请求用户允许使用他/她的麦克风的函数）：

window.addEventListener('load', initAudio );

现在，我在 HTML 中添加了以下代码：

<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>

正如你所看到的，我称之为切换录音（这个）仅在按下 #recbutton 后才执行功能（启动录制过程的功能）。现在，这段代码一切正常，但是，页面加载后，用户会收到麦克风权限提示，我想仅在他们单击 #recbutton 后才请求他们获得使用麦克风的权限，你明白我的意思吗？我认为如果我删除第一个文件的最后一行：

window.addEventListener('load', initAudio );

并像这样修改我的嵌入脚本：

<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>

我也许能够实现我想要的，实际上我是这样，用户在单击 #recbutton 之前不会收到有关他/她的麦克风的提示。问题是，音频永远不会被录制，当您尝试下载它时，生成的 WAV 是空的。

我怎样才能解决这个问题？

我的项目代码位于：https://github.com/Jmlevick/html-recorder https://github.com/Jmlevick/html-recorder

不，你的问题是 getUserMedia() 有一个异步回调（gotMedia()）；您需要在该回调内的开始按钮调用（特别是toggleRecording位）中包含其余的代码逻辑，因为现在它是在 getUserMedia 返回（并设置音频节点）之前执行的。