ljm_j1/modules/RTC/CodecSelection.js

import { getLogger } from 'jitsi-meet-logger';

import * as JitsiConferenceEvents from '../../JitsiConferenceEvents';
import CodecMimeType from '../../service/RTC/CodecMimeType';
import * as MediaType from '../../service/RTC/MediaType';
import browser from '../browser';

const logger = getLogger(__filename);

/**
 * This class handles the codec selection mechanism for the conference based on the config.js settings.
 * The preferred codec is selected based on the settings and the list of codecs supported by the browser.
 * The preferred codec is published in presence which is then used by the other endpoints in the
 * conference to pick a supported codec at join time and when the call transitions between p2p and jvb
 * connections.
 */
export class CodecSelection {
    /**
     * Creates a new instance for a given conference.
     *
     * @param {JitsiConference} conference the conference instance
     * @param {*} options
     * @param {string} options.disabledCodec the codec that needs to be disabled.
     * @param {boolean} options.enforcePreferredCodec whether codec preference has to be
     * enforced even when an endpoints that doesn't support the preferred codec joins the call.
     * Falling back to the standard codec will be skipped when this option is true, endpoints
     * that do not support the preferred codec may not be able to encode/decode video when this happens.
     * @param {string} options.jvbCodec the codec that is preferred on jvb connection.
     * @param {string} options.p2pCodec the codec that is preferred on p2p connection.
     */
    constructor(conference, options) {
        this.conference = conference;
        this.options = options;

        // VP8 cannot be disabled and it will be the default codec when no preference is set.
        this.disabledCodec = options.disabledCodec === CodecMimeType.VP8
            ? undefined
            : this._getCodecMimeType(options.disabledCodec);

        // Check if the codec values passed are valid.
        const jvbCodec = this._getCodecMimeType(options.jvbCodec);
        const p2pCodec = this._getCodecMimeType(options.p2pCodec);

        this.jvbPreferredCodec = jvbCodec && this._isCodecSupported(jvbCodec) ? jvbCodec : CodecMimeType.VP8;
        this.p2pPreferredCodec = p2pCodec && this._isCodecSupported(p2pCodec) ? p2pCodec : CodecMimeType.VP8;
        logger.debug(`Codec preferences for the conference are JVB: ${this.jvbPreferredCodec},
            P2P: ${this.p2pPreferredCodec}`);

        if (this.jvbPreferredCodec === CodecMimeType.VP9 && !browser.supportsVP9()) {
            this.jvbPreferredCodec = CodecMimeType.VP8;
        }

        this.conference.on(
            JitsiConferenceEvents.USER_JOINED,
            () => this._selectPreferredCodec());
        this.conference.on(
            JitsiConferenceEvents.USER_LEFT,
            () => this._selectPreferredCodec());
        this.conference.on(
            JitsiConferenceEvents._MEDIA_SESSION_STARTED,
            session => this._onMediaSessionStared(session));
    }

    /**
     * Checks if a given string is a valid video codec mime type.
     *
     * @param {string} codec the codec string that needs to be validated.
     * @returns {CodecMimeType|null} mime type if valid, null otherwise.
     * @private
     */
    _getCodecMimeType(codec) {
        if (typeof codec === 'string') {
            return Object.values(CodecMimeType).find(value => value === codec.toLowerCase());
        }

        return null;
    }

    /**
     * Checks if the given codec is supported by the browser.
     *
     * @param {CodecMimeType} preferredCodec codec to be checked.
     * @returns {boolean} true if the given codec is supported, false otherwise.
     * @private
     */
    _isCodecSupported(preferredCodec) {
        // Skip the check on FF and RN because they do not support the getCapabilities API.
        // It is safe to assume both of them support all the codecs supported by Chrome.
        if (browser.isFirefox() || browser.isReactNative()) {
            return true;
        }

        return window.RTCRtpReceiver
            && window.RTCRtpReceiver.getCapabilities
            && window.RTCRtpReceiver.getCapabilities('video').codecs
            .some(codec => codec.mimeType.toLowerCase() === `video/${preferredCodec}`);
    }

    /**
     * Handles the {@link JitsiConferenceEvents._MEDIA_SESSION_STARTED} event. Codecs need to be
     * configured on the media session that is newly created.
     *
     * @param {JingleSessionPC} mediaSession media session that started.
     * @returns {void}
     * @private
     */
    _onMediaSessionStared(mediaSession) {
        const preferredCodec = mediaSession.isP2P ? this.p2pPreferredCodec : this.jvbPreferredCodec;
        const disabledCodec = this.disabledCodec && this._isCodecSupported(this.disabledCodec)
            ? this.disabledCodec
            : null;

        this._selectPreferredCodec(mediaSession, preferredCodec, disabledCodec);
    }

    /**
     * Sets the codec on the media session based on the preferred codec setting and the supported codecs
     * published by the remote participants in their presence.
     *
     * @param {JingleSessionPC} mediaSession session for which the codec selection has to be made.
     * @param {CodecMimeType} preferredCodec preferred codec.
     * @param {CodecMimeType} disabledCodec codec that needs to be disabled.
     */
    _selectPreferredCodec(mediaSession = null, preferredCodec = null, disabledCodec = null) {
        const session = mediaSession ? mediaSession : this.conference.jvbJingleSession;
        const currentCodec = preferredCodec ? preferredCodec : this.jvbPreferredCodec;
        let selectedCodec = currentCodec;

        if (session && !session.isP2P && !this.options.enforcePreferredCodec) {
            const remoteParticipants = this.conference.getParticipants().map(participant => participant.getId());

            for (const remote of remoteParticipants) {
                const peerMediaInfo = session._signalingLayer.getPeerMediaInfo(remote, MediaType.VIDEO);
                const peerCodec = peerMediaInfo?.codecType;

                if (peerCodec
                    && peerCodec !== currentCodec
                    && (peerCodec !== CodecMimeType.VP9 || browser.supportsVP9())) {
                    selectedCodec = peerCodec;
                }
            }
        }
        session && session.setVideoCodecs(selectedCodec, disabledCodec);
    }

    /**
     * Returns the preferred codec for the conference. The preferred codec for the JVB media session
     * is the one that gets published in presence and a comparision is made whenever a participant joins
     * or leaves the call.
     *
     * @returns {CodecMimeType} preferred codec.
     */
    getPreferredCodec() {
        return this.jvbPreferredCodec;
    }
}