audio-vis/raw/javascript/audio.js

const AudioContext = window.AudioContext || window.webkitAudioContext;

class AudioHandler {
    async init() {
        let self = this;
        self.isStarted = false;
        self.audioFile = new Audio();
        self.actx = new AudioContext();
        self.analyser = self.actx.createAnalyser();
        self.analyser.fftSize = 4096;
        self.lastSong = null;
        await self.connectAll();
    }

    async connectAll() {
        let self = this;
        self.source = self.actx.createMediaElementSource(self.audioFile);
        self.source.connect(self.analyser);
        self.analyser.connect(self.actx.destination);
        self.audioFile.addEventListener('ended', player.nextSong.bind(player));
    }

    async start() {
        if (this.audioFile.src === '') {
            return;
        }
        if (!this.isStarted) {
            this.isStarted = true;
            await this.actx.resume();
        }
    }

    async stop() {
        if (this.isStarted) {
            this.isStarted = false;
            await this.actx.suspend();
        }
    }

    fftSize(size) {
        this.analyser.fftSize = size;
    }

    smoothing(float) {
        this.analyser.smoothingTimeConstant = float;
    }

    loadSong(src) {
        let self = this;
        if (self.lastSong) {
            URL.revokeObjectURL(self.lastSong);
        }
        self.lastSong = this.audioFile.src = URL.createObjectURL(src);
        if (!this.isStarted) {
            this.start().catch(alert);
        }
        this.audioFile.play().then(e => {
            window.dispatchEvent(new CustomEvent('playSong'));
        }).catch(e => {
            player.nextSong();
        });
    }

    getIntArray(steps) {
        let dataArray = new Uint8Array(steps);
        this.analyser.getByteFrequencyData(dataArray);
        return dataArray;
    }

    getFloatArray() {
        let dataArray = new Float32Array(this.analyser.fftSize);
        this.analyser.getFloatTimeDomainData(dataArray);
        return dataArray;
    }
}