如何使用 Javascript 编写音频可视化器

Question

我正在尝试编写这个特殊的音频可视化代码：https://codepen.io/nfj525/pen/rVBaab。

我正在苦苦挣扎，因为我不想像示例中那样上传音频文件，而是希望通过单击音频的播放按钮来运行代码。我想使用我自己预先存在的音频并播放它，而不必上传文件。我是编码新手，我不确定如何编辑 javascript 来做到这一点。

这是我在要播放的音频中添加的html，“song.mp3”

<div id="content">
  <input type="file" id="thefile" accept="audio/*" />
  <canvas id="canvas"></canvas>
  <audio src="song.mp3" id="audio" controls></audio>
</div>

这就是它的js

window.onload = function() {

  var file = document.getElementById("thefile");
  var audio = document.getElementById("audio");

  file.onchange = function() {
    var files = this.files;
    audio.src = URL.createObjectURL(files[0]);
    audio.load();
    audio.play();
    var context = new AudioContext();
    var src = context.createMediaElementSource(audio);
    var analyser = context.createAnalyser();

    var canvas = document.getElementById("canvas");
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight;
    var ctx = canvas.getContext("2d");

    src.connect(analyser);
    analyser.connect(context.destination);

    analyser.fftSize = 256;

    var bufferLength = analyser.frequencyBinCount;
    console.log(bufferLength);

    var dataArray = new Uint8Array(bufferLength);

    var WIDTH = canvas.width;
    var HEIGHT = canvas.height;

    var barWidth = (WIDTH / bufferLength) * 2.5;
    var barHeight;
    var x = 0;

    function renderFrame() {
      requestAnimationFrame(renderFrame);

      x = 0;

      analyser.getByteFrequencyData(dataArray);

      ctx.fillStyle = "#000";
      ctx.fillRect(0, 0, WIDTH, HEIGHT);

      for (var i = 0; i < bufferLength; i++) {
        barHeight = dataArray[i];

        var r = barHeight + (25 * (i/bufferLength));
        var g = 250 * (i/bufferLength);
        var b = 50;

        ctx.fillStyle = "rgb(" + r + "," + g + "," + b + ")";
        ctx.fillRect(x, HEIGHT - barHeight, barWidth, barHeight);

        x += barWidth + 1;
      }
    }

    audio.play();
    renderFrame();
  };
};

Answer 1

因此，为此，您的 html 中不再需要文件输入元素，因此您的第一部分变为：

    <div id="content">
      <canvas id="canvas"></canvas>
      <audio src="song.mp3" id="audio" controls></audio>
    </div>

至于 Javascript，还有一些工作要做。总之，我们将提取并命名实际完成整个工作的函数，然后在window.onload 事件上调用它。所以你的脚本部分应该是这样的：

<script>
    function playAudio() {
            var audio = document.getElementById("audio");
            // var files = this.files;  // not needed
            // audio.src = URL.createObjectURL(files[0]);  // not needed
            audio.load();
            audio.play();
            var context = new AudioContext();
            var src = context.createMediaElementSource(audio);
            var analyser = context.createAnalyser();

            var canvas = document.getElementById("canvas");
            canvas.width = window.innerWidth;
            canvas.height = window.innerHeight;
            var ctx = canvas.getContext("2d");

            src.connect(analyser);
            analyser.connect(context.destination);

            analyser.fftSize = 256;

            var bufferLength = analyser.frequencyBinCount;
            console.log(bufferLength);

            var dataArray = new Uint8Array(bufferLength);

            var WIDTH = canvas.width;
            var HEIGHT = canvas.height;

            var barWidth = WIDTH / bufferLength * 2.5;
            var barHeight;
            var x = 0;

            function renderFrame() {
              requestAnimationFrame(renderFrame);

              x = 0;

              analyser.getByteFrequencyData(dataArray);

              ctx.fillStyle = "#000";
              ctx.fillRect(0, 0, WIDTH, HEIGHT);

              for (var i = 0; i < bufferLength; i++) {
                barHeight = dataArray[i];

                var r = barHeight + 25 * (i / bufferLength);
                var g = 250 * (i / bufferLength);
                var b = 50;

                ctx.fillStyle = "rgb(" + r + "," + g + "," + b + ")";
                ctx.fillRect(x, HEIGHT - barHeight, barWidth, barHeight);

                x += barWidth + 1;
              }
            }

            audio.play();
            renderFrame();
          };

        window.onload = function () {
          // start playing audio once the page is fully loaded
          playAudio();
        };
</script>

请注意，这必须托管在某个服务器上。