javascript - 删除 createMediaElementSource

Question

我已经为这个问题到处搜索，但找不到任何东西。我处于需要删除 source = createMediaElementSource 以便重新创建它的情况。我正在使用音频分析器，每次使用 ajax 加载指定轨道时都必须加载它。一旦你转到另一个页面，然后返回，分析器就消失了。因此我需要以某种方式重新初始化它。

我的代码:

var analyserElement = document.getElementById('analyzer');
var canvas, ctx, source, context, analyser, fbc_array, bars, bar_x,
    bar_width, bar_height;

function analyzerSetElements() {
    var analyserElement = document.getElementById('analyzer');
}

function analyzerInitialize() {
    if (context == undefined) {
    context = new AudioContext();
    }
    analyser = context.createAnalyser();
    canvas = analyserElement;
    ctx = canvas.getContext('2d');
    source = context.createMediaElementSource(audio);
    source.connect(analyser);
    analyser.connect(context.destination);
    frameLooper();
}

function analyzerStop(){
    context = undefined;
    analyser = undefined;
    source = undefined;
}

function frameLooper() {
    canvas.width = canwidth;
    canvas.height = canheight;
    ctx.imageSmoothingEnabled = false;
    fbc_array = new Uint8Array(analyser.frequencyBinCount);
    analyser.getByteFrequencyData(fbc_array);
    ctx.clearRect(0, 0, canvas.width, canvas.height); // Clear the canvas
    ctx.fillStyle = "white"; // Color of the bars
    function valBetween(v, min, max) {
        return (Math.min(max, Math.max(min, v)));
    }
    var beatc = fbc_array[2] / 4;
    var beatround = Math.round(beatc);
    //if (beatround < 10) {
    //    ctx.globalAlpha = '0.1125';
    //}
    //else {
    //    ctx.globalAlpha = '0.' + beatround;
    //}
    bars = canbars;
    for (var i = 0; i < bars; i += canmultiplier) {
        bar_x = i * canspace;
        bar_width = 2;
        bar_height = -3 - (fbc_array[i] / 2);
        ctx.fillRect(bar_x, canvas.height, bar_width, bar_height);
    }
    window.requestAnimationFrame(frameLooper);
    console.log('Looped')
}

因此，当我在运行 analyzerStop() 之后运行 analyzerInitialize() 时，我仍然会收到此错误:

audio.js:179 Uncaught DOMException: Failed to execute 'createMediaElementSource' on 'AudioContext': HTMLMediaElement already connected previously to a different MediaElementSourceNode

我怎样才能使 analyzerInitialize() 永远不会失败？

Answer 1

我遇到过同样的问题。不幸的是，我没有找到如何从音频元素中获取已创建的 MediaElementSourceNode。尽管如此，还是可以通过使用 WeakMap 来记住 MediaElementSourceNode 来解决这个问题:

var MEDIA_ELEMENT_NODES = new WeakMap();

function analyzerInitialize() {
  if (context == undefined) {
    context = new AudioContext();
  }
  analyser = context.createAnalyser();
  canvas = analyserElement;
  ctx = canvas.getContext('2d');
  if (MEDIA_ELEMENT_NODES.has(audio)) {
    source = MEDIA_ELEMENT_NODES.get(audio);
  } else {
    source = context.createMediaElementSource(audio);
    MEDIA_ELEMENT_NODES.set(audio, source);
  }
  source.connect(analyser);
  analyser.connect(context.destination);
  frameLooper();
}

通过使用 WeakMap 我避免了内存问题。