ljm0/modules/statistics/LocalStatsCollector.ts

import { getLogger } from '@jitsi/logger';

const logger = getLogger('modules/statistics/LocalStatsCollector');
/**
 * Size of the webaudio analyzer buffer.
 * @type {number}
 */
const WEBAUDIO_ANALYZER_FFT_SIZE: number = 2048;

/**
 * Value of the webaudio analyzer smoothing time parameter.
 * @type {number}
 */
const WEBAUDIO_ANALYZER_SMOOTING_TIME: number = 0.8;

/**
 * The audio context.
 * @type {AudioContext}
 */
let context: AudioContext | null = null;

/**
 * Converts time domain data array to audio level.
 * @param samples the time domain data array.
 * @returns {number} the audio level
 */
function timeDomainDataToAudioLevel(samples: Uint8Array): number {
    let maxVolume = 0;
    const length = samples.length;

    for (let i = 0; i < length; i++) {
        if (maxVolume < samples[i]) {
            maxVolume = samples[i];
        }
    }

    return Number.parseFloat(((maxVolume - 127) / 128).toFixed(3));
}

/**
 * Animates audio level change
 * @param newLevel the new audio level
 * @param lastLevel the last audio level
 * @returns {Number} the audio level to be set
 */
function animateLevel(newLevel: number, lastLevel: number): number {
    let value = 0;
    const diff = lastLevel - newLevel;

    if (diff > 0.2) {
        value = lastLevel - 0.2;
    } else if (diff < -0.4) {
        value = lastLevel + 0.4;
    } else {
        value = newLevel;
    }

    return Number.parseFloat(value.toFixed(3));
}

/**
 * Provides statistics for the local stream.
 */
export default class LocalStatsCollector {
    stream: MediaStream;
    intervalId: Timeout | null;
    intervalMilis: number;
    audioLevel: number;
    callback: (audioLevel: number) => void;
    source: MediaStreamAudioSourceNode | null;
    analyser: AnalyserNode | null;

    /**
     * Creates a new instance of LocalStatsCollector.
     *
     * @param {MediaStream} stream - the local stream
     * @param {number} interval - stats refresh interval given in ms.
     * @param {Function} callback - function that receives the audio levels.
     * @constructor
     */
    constructor(
            stream: MediaStream,
            interval: number,
            callback: (audioLevel: number) => void
    ) {
        this.stream = stream;
        this.intervalId = null;
        this.intervalMilis = interval;
        this.audioLevel = 0;
        this.callback = callback;
        this.source = null;
        this.analyser = null;
    }

    /**
     * Starts the collecting the statistics.
     */
    start(): void {
        if (!LocalStatsCollector.isLocalStatsSupported()) {
            return;
        }

        context!.resume();
        this.analyser = context!.createAnalyser();

        this.analyser.smoothingTimeConstant = WEBAUDIO_ANALYZER_SMOOTING_TIME;
        this.analyser.fftSize = WEBAUDIO_ANALYZER_FFT_SIZE;

        this.source = context!.createMediaStreamSource(this.stream);

        this.source.connect(this.analyser);

        this.intervalId = setInterval(
            () => {
                const array = new Uint8Array(this.analyser!.frequencyBinCount);

                this.analyser!.getByteTimeDomainData(array);
                const audioLevel = timeDomainDataToAudioLevel(array);

                // Set the audio levels always as NoAudioSignalDetection now
                // uses audio levels from LocalStatsCollector and waits for
                // atleast 4 secs for a no audio signal before displaying the
                // notification on the UI.
                this.audioLevel = animateLevel(audioLevel, this.audioLevel);
                this.callback(this.audioLevel);
            },
            this.intervalMilis
        );
    }

    /**
     * Stops collecting the statistics.
     */
    stop(): void {
        if (this.intervalId) {
            clearInterval(this.intervalId);
            this.intervalId = null;
        }

        this.analyser?.disconnect();
        this.analyser = null;
        this.source?.disconnect();
        this.source = null;
    }

    /**
     * Initialize collector.
     */
    static init(): void {
        LocalStatsCollector.connectAudioContext();
    }

    /**
     * Checks if the environment has the necessary conditions to support
     * collecting stats from local streams.
     *
     * @returns {boolean}
     */
    static isLocalStatsSupported(): boolean {
        return Boolean(window?.AudioContext);
    }

    /**
     * Disconnects the audio context.
     */
    static async disconnectAudioContext(): Promise<void> {
        if (context) {
            logger.info('Disconnecting audio context');
            await context.close();
            context = null;
        }
    }

    /**
     * Connects the audio context.
     */
    static connectAudioContext(): void {
        if (!LocalStatsCollector.isLocalStatsSupported()) {
            return;
        }

        logger.info('Connecting audio context');
        context = new AudioContext();

        context.suspend();
    }
}