音声をオシロスコープみたいに表示

![スクリーンショット 2020-08-29 11.55.43.png](https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/117164/1a5c7961-b2b6-7926-cd40-d98ca6d63e5c.png)

``` html
<!DOCTYPE html>
<html lang='ja'>

<head>
    <title>Recording to WebSocket</title>
    <meta http-equiv='Content-Type' content='text/html; charset=utf-8' />
    <meta http-equiv="Pragma" content="no-cache">
    <meta http-equiv="Cache-Control" content="no-cache">
</head>

<body>

    <canvas id="canvas" width="380" height="80"></canvas>
    <div>
        <button class='start'>start</button>
        <button class='stop' disabled>stop</button>
    </div>

    <script>

        const canvas = document.getElementById('canvas');
        const _CanvasRenderingContext2D = canvas.getContext('2d');

        const bufferSize = 0 //256, 512, 1024, 2048, 4096, 8192, 16384
        const numberOfInputChannels = 1
        const numberOfOutputChannels = 1

        const startButton = document.querySelector(".start")
        const stopButton = document.querySelector(".stop")

        if (!navigator.getUserMedia)
            navigator.getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia

        var _MediaStream

        // ---------------------------------------------
        // Start Button
        // ---------------------------------------------
        startButton.onclick = () => {
            startButton.disabled = true
            stopButton.disabled = !startButton.disabled

            var _AudioContext = new (window.AudioContext || window.webkitAudioContext)();

            // ##############################################
            // #   Recording
            // ##############################################
            navigator.mediaDevices.getUserMedia({ audio: true, video: false }).then((constraints) => {
                console.log('start recording')

                _MediaStream = constraints

                var _MediaStreamAudioSourceNode = _AudioContext.createMediaStreamSource(constraints)
                _ScriptProcessorNode = _AudioContext.createScriptProcessor(bufferSize, numberOfInputChannels, numberOfOutputChannels)
                _ScriptProcessorNode.onaudioprocess = (_AudioProcessingEvent) => {

                    let dataArray = new Uint8Array(_AnalyserNode.fftSize);
                    _AnalyserNode.getByteTimeDomainData(dataArray);
                    visualize(dataArray, _AnalyserNode.fftSize);

                }
                _MediaStreamAudioSourceNode.connect(_ScriptProcessorNode)
                _ScriptProcessorNode.connect(_AudioContext.destination)

                _CanvasRenderingContext2D.fillStyle = "rgb(30, 30, 30)";
                _CanvasRenderingContext2D.lineWidth = 1;
                _CanvasRenderingContext2D.strokeStyle = "rgb(0, 250, 30)";

                var _AnalyserNode = _AnalyserNode = _AudioContext.createAnalyser();
                //_AnalyserNode.fftSize = 2048;
                _MediaStreamAudioSourceNode.connect(_AnalyserNode);

            }).catch((err) => {
                console.log(err);
            })

        }

        // ---------------------------------------------
        // Stop Button
        // ---------------------------------------------
        stopButton.onclick = () => {
            if (!startButton.disabled)
                return
            startButton.disabled = false
            stopButton.disabled = !startButton.disabled
            _MediaStream.getTracks().forEach((_MediaStreamTrack) => {
                _MediaStreamTrack.stop()
                console.log('stop recording')
            })
        }

        // ---------------------------------------------
        // Audio Visualizer
        // ---------------------------------------------
        function visualize(dataArray, bufferLength) {
            _CanvasRenderingContext2D.fillRect(0, 0, canvas.width, canvas.height);
            _CanvasRenderingContext2D.beginPath();
            var sliceWidth = (canvas.width * 1.0) / bufferLength;
            var x = 0;
            for (var i = 0; i < bufferLength; i++) {
                var v = dataArray[i] / 128.0;
                var y = (v * canvas.height) / 2;
                i === 0 ? _CanvasRenderingContext2D.moveTo(x, y) : _CanvasRenderingContext2D.lineTo(x, y);
                x += sliceWidth;
            }
            _CanvasRenderingContext2D.lineTo(canvas.width, canvas.height / 2);
            _CanvasRenderingContext2D.stroke();
        }

    </script>
</body>

</html>