Spectrogram/audiio.html at main · gorillaPet/Spectrogram · GitHub

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<!DOCTYPE html>
<html>

<head>
<style>


.visualiser-container {
    position: absolute;
    top: 200px;
    left: 0;
    right: 0;
    height: 200px;
}

canvas {
    position: absolute;
    top: 0;
    left: 0;
}

#playhead {
    position: absolute;
    top: 0;
    width: 2px;
    height: 200px;
    background: white;
    z-index: 2;
}

</style>
</head>

<body>

<audio src="audio_test.mp3" controls style="position: absolute; z-index: 3;"></audio>

<div class="visualiser-container">
    <canvas id="spectrogram"></canvas>
    <div id="playhead"></div>
</div>

<script>
(function() {

    const audio = document.querySelector("audio");

    const canvas = document.getElementById("spectrogram");
    const ctx = canvas.getContext("2d");

    const playhead = document.getElementById("playhead");

    canvas.width = window.innerWidth;
    canvas.height = 200;

    async function generateSpectrogram() {

        const context = new AudioContext();

        // fetch + decode full audio buffer
        const response = await fetch(audio.src);
        const arrayBuffer = await response.arrayBuffer();
        const audioBuffer = await context.decodeAudioData(arrayBuffer);

        const analyser = context.createAnalyser();
        analyser.fftSize = 2048;

        const bufferSource = context.createBufferSource();
        bufferSource.buffer = audioBuffer;

        bufferSource.connect(analyser);

        const freqData = new Uint8Array(analyser.frequencyBinCount);

        const duration = audioBuffer.duration;

        const step = 0.005; // seconds per slice (controls horizontal resolution)
        const totalSlices = Math.floor(duration / step);

        const sliceWidth = canvas.width / totalSlices;

        // offline processing
        for (let i = 0; i < totalSlices; i++) {

            const time = i * step;

            // create tiny buffer slice
            const tempSource = context.createBufferSource();
            tempSource.buffer = audioBuffer;
            tempSource.connect(analyser);

            tempSource.start(0, time, step);

            await new Promise(r => setTimeout(r, 1)); // allow analyser to fill

            analyser.getByteFrequencyData(freqData);

            for (let j = 0; j < freqData.length; j++) {

                const value = freqData[j];
                const percent = value / 255;

                const y = canvas.height - (j / freqData.length) * canvas.height;

                const hue = 240 - percent * 240;

                ctx.fillStyle = `hsl(${hue}, 100%, ${percent * 50}%)`;

                ctx.fillRect(i * sliceWidth, y, sliceWidth, canvas.height / freqData.length);
            }
        }
    }

    function animatePlayhead() {
        requestAnimationFrame(animatePlayhead);

        const percent = audio.currentTime / audio.duration;
        const x = percent * canvas.width;

        playhead.style.left = x + "px";
    }

    audio.onplay = () => {
        animatePlayhead();
    };

    generateSpectrogram();

})();
</script>

</body>
</html>