BolaRule.js

/**
 * The copyright in this software is being made available under the BSD License,
 * included below. This software may be subject to other third party and contributor
 * rights, including patent rights, and no such rights are granted under this license.
 *
 * Copyright (c) 2016, Dash Industry Forum.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *  * Redistributions of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation and/or
 *  other materials provided with the distribution.
 *  * Neither the name of Dash Industry Forum nor the names of its
 *  contributors may be used to endorse or promote products derived from this software
 *  without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS AS IS AND ANY
 *  EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 *  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 *  IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 *  INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 *  WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 *  POSSIBILITY OF SUCH DAMAGE.
 */

// For a description of the BOLA adaptive bitrate (ABR) algorithm, see http://arxiv.org/abs/1601.06748

import MetricsConstants from '../../constants/MetricsConstants';
import SwitchRequest from '../SwitchRequest';
import FactoryMaker from '../../../core/FactoryMaker';
import {HTTPRequest} from '../../vo/metrics/HTTPRequest';
import EventBus from '../../../core/EventBus';
import Events from '../../../core/events/Events';
import Debug from '../../../core/Debug';

// BOLA_STATE_ONE_BITRATE   : If there is only one bitrate (or initialization failed), always return NO_CHANGE.
// BOLA_STATE_STARTUP       : Set placeholder buffer such that we download fragments at most recently measured throughput.
// BOLA_STATE_STEADY        : Buffer primed, we switch to steady operation.
// TODO: add BOLA_STATE_SEEK and tune BOLA behavior on seeking
const BOLA_STATE_ONE_BITRATE    = 0;
const BOLA_STATE_STARTUP        = 1;
const BOLA_STATE_STEADY         = 2;

const MINIMUM_BUFFER_S = 10; // BOLA should never add artificial delays if buffer is less than MINIMUM_BUFFER_S.
const MINIMUM_BUFFER_PER_BITRATE_LEVEL_S = 2;
// E.g. if there are 5 bitrates, BOLA switches to top bitrate at buffer = 10 + 5 * 2 = 20s.
// If Schedule Controller does not allow buffer to reach that level, it can be achieved through the placeholder buffer level.

const PLACEHOLDER_BUFFER_DECAY = 0.99; // Make sure placeholder buffer does not stick around too long.

function BolaRule(config) {

    const context = this.context;
    const log = Debug(context).getInstance().log;
    const dashMetrics = config.dashMetrics;
    const metricsModel = config.metricsModel;
    const mediaPlayerModel = config.mediaPlayerModel;
    const eventBus = EventBus(context).getInstance();

    let instance,
        bolaStateDict;

    function setup() {
        resetInitialSettings();

        eventBus.on(Events.BUFFER_EMPTY, onBufferEmpty, instance);
        eventBus.on(Events.PLAYBACK_SEEKING, onPlaybackSeeking, instance);
        eventBus.on(Events.PERIOD_SWITCH_STARTED, onPeriodSwitchStarted, instance);
        eventBus.on(Events.MEDIA_FRAGMENT_LOADED, onMediaFragmentLoaded, instance);
        eventBus.on(Events.METRIC_ADDED, onMetricAdded, instance);
        eventBus.on(Events.QUALITY_CHANGE_REQUESTED, onQualityChangeRequested, instance);
        eventBus.on(Events.FRAGMENT_LOADING_ABANDONED, onFragmentLoadingAbandoned, instance);
    }

    function utilitiesFromBitrates(bitrates) {
        return bitrates.map(b => Math.log(b));
        // no need to worry about offset, utilities will be offset (uniformly) anyway later
    }

    // NOTE: in live streaming, the real buffer level can drop below minimumBufferS, but bola should not stick to lowest bitrate by using a placeholder buffer level
    function calculateBolaParameters(stableBufferTime, bitrates, utilities) {
        let highestUtilityIndex = utilities.reduce((highestIndex, u, uIndex) => (u > utilities[highestIndex] ? uIndex : highestIndex), 0);

        if (highestUtilityIndex === 0) {
            // if highestUtilityIndex === 0, then always use lowest bitrate
            return null;
        }

        let bufferTime = Math.max(stableBufferTime, MINIMUM_BUFFER_S + MINIMUM_BUFFER_PER_BITRATE_LEVEL_S * bitrates.length);

        // TODO: Investigate if following can be better if utilities are not the default Math.log utilities.
        // If using Math.log utilities, we can choose Vp and gp to always prefer bitrates[0] at minimumBufferS and bitrates[max] at bufferTarget.
        // (Vp * (utility + gp) - bufferLevel) / bitrate has the maxima described when:
        // Vp * (utilities[0] + gp - 1) === minimumBufferS and Vp * (utilities[max] + gp - 1) === bufferTarget
        // giving:
        const gp = (utilities[highestUtilityIndex] - 1) / (bufferTime / MINIMUM_BUFFER_S - 1);
        const Vp = MINIMUM_BUFFER_S / gp;
        // note that expressions for gp and Vp assume utilities[0] === 1, which is true because of normalization

        return {gp: gp, Vp: Vp};
    }

    function getInitialBolaState(rulesContext) {
        let initialState = {};

        const mediaInfo = rulesContext.getMediaInfo();
        const bitrates = mediaInfo.bitrateList.map(b => b.bandwidth);
        let utilities = utilitiesFromBitrates(bitrates);
        utilities = utilities.map(u => u - utilities[0] + 1); // normalize
        let stableBufferTime = mediaPlayerModel.getStableBufferTime();
        const params = calculateBolaParameters(stableBufferTime, bitrates, utilities);

        if (!params) {
            // only happens when there is only one bitrate level
            initialState.state = BOLA_STATE_ONE_BITRATE;
        } else {
            initialState.state = BOLA_STATE_STARTUP;

            initialState.bitrates = bitrates;
            initialState.utilities = utilities;
            initialState.stableBufferTime = stableBufferTime;
            initialState.Vp = params.Vp;
            initialState.gp = params.gp;

            initialState.lastQuality = 0;
            clearBolaStateOnSeek(initialState);
        }

        return initialState;
    }

    function clearBolaStateOnSeek(bolaState) {
        bolaState.placeholderBuffer = 0;
        bolaState.mostAdvancedSegmentStart = NaN;
        bolaState.lastSegmentWasReplacement = false;
        bolaState.lastSegmentStart = NaN;
        bolaState.lastSegmentDurationS = NaN;
        bolaState.lastSegmentRequestTimeMs = NaN;
        bolaState.lastSegmentFinishTimeMs = NaN;
    }

    // If the buffer target is changed (can this happen mid-stream?), then adjust BOLA parameters accordingly.
    function checkBolaStateStableBufferTime(bolaState, mediaType) {
        let stableBufferTime = mediaPlayerModel.getStableBufferTime();
        if (bolaState.stableBufferTime !== stableBufferTime) {
            const params = calculateBolaParameters(stableBufferTime, bolaState.bitrates, bolaState.utilities);
            if (params.Vp !== bolaState.Vp || params.gp !== bolaState.gp) {
                // correct placeholder buffer using two criteria:
                // 1. do not change effective buffer level at effectiveBufferLevel === MINIMUM_BUFFER_S ( === Vp * gp )
                // 2. scale placeholder buffer by Vp subject to offset indicated in 1.

                let bufferLevel = dashMetrics.getCurrentBufferLevel(metricsModel.getReadOnlyMetricsFor(mediaType));
                let effectiveBufferLevel = bufferLevel + bolaState.placeholderBuffer;

                effectiveBufferLevel -= MINIMUM_BUFFER_S;
                effectiveBufferLevel *= params.Vp / bolaState.Vp;
                effectiveBufferLevel += MINIMUM_BUFFER_S;

                bolaState.stableBufferTime = stableBufferTime;
                bolaState.Vp = params.Vp;
                bolaState.gp = params.gp;
                bolaState.placeholderBuffer = Math.max(0, effectiveBufferLevel - bufferLevel);
            }
        }
    }

    function getBolaState(rulesContext) {
        const mediaType = rulesContext.getMediaType();
        let bolaState = bolaStateDict[mediaType];
        if (!bolaState) {
            bolaState = getInitialBolaState(rulesContext);
            bolaStateDict[mediaType] = bolaState;
        } else if (bolaState.state !== BOLA_STATE_ONE_BITRATE) {
            checkBolaStateStableBufferTime(bolaState, mediaType);
        }
        return bolaState;
    }

    // The core idea of BOLA.
    function getQualityFromBufferLevel(bolaState, bufferLevel) {
        const bitrateCount = bolaState.bitrates.length;
        let quality = NaN;
        let score = NaN;
        for (let i = 0; i < bitrateCount; ++i) {
            let s = (bolaState.Vp * (bolaState.utilities[i] + bolaState.gp) - bufferLevel) / bolaState.bitrates[i];
            if (isNaN(score) || s >= score) {
                score = s;
                quality = i;
            }
        }
        return quality;
    }

    // maximum buffer level which prefers to download at quality rather than wait
    function maxBufferLevelForQuality(bolaState, quality) {
        return bolaState.Vp * (bolaState.utilities[quality] + bolaState.gp);
    }

    // the minimum buffer level that would cause BOLA to choose quality rather than a lower bitrate
    function minBufferLevelForQuality(bolaState, quality) {
        let qBitrate = bolaState.bitrates[quality];
        let qUtility = bolaState.utilities[quality];

        let min = 0;
        for (let i = quality - 1; i >= 0; --i) {
            // for each bitrate less than bitrates[quality], BOLA should prefer quality (unless other bitrate has higher utility)
            if (bolaState.utilities[i] < bolaState.utilities[quality]) {
                let iBitrate = bolaState.bitrates[i];
                let iUtility = bolaState.utilities[i];

                let level = bolaState.Vp * (bolaState.gp + (qBitrate * iUtility - iBitrate * qUtility) / (qBitrate - iBitrate));
                min = Math.max(min, level); // we want min to be small but at least level(i) for all i
            }
        }
        return min;
    }

    /*
     * The placeholder buffer increases the effective buffer that is used to calculate the bitrate.
     * There are two main reasons we might want to increase the placeholder buffer:
     *
     * 1. When a segment finishes downloading, we would expect to get a call on getMaxIndex() regarding the quality for
     *    the next segment. However, there might be a delay before the next call. E.g. when streaming live content, the
     *    next segment might not be available yet. If the call to getMaxIndex() does happens after a delay, we don't
     *    want the delay to change the BOLA decision - we only want to factor download time to decide on bitrate level.
     *
     * 2. It is possible to get a call to getMaxIndex() without having a segment download. The buffer target in dash.js
     *    is different for top-quality segments and lower-quality segments. If getMaxIndex() returns a lower-than-top
     *    quality, then the buffer controller might decide not to download a segment. When dash.js is ready for the next
     *    segment, getMaxIndex() will be called again. We don't want this extra delay to factor in the bitrate decision.
     */
    function updatePlaceholderBuffer(bolaState, mediaType) {
        let nowMs = Date.now();

        if (!isNaN(bolaState.lastSegmentFinishTimeMs)) {
            // compensate for non-bandwidth-derived delays, e.g., live streaming availability, buffer controller
            let delay = 0.001 * (nowMs - bolaState.lastSegmentFinishTimeMs);
            bolaState.placeholderBuffer += Math.max(0, delay);
        } else if (!isNaN(bolaState.lastCallTimeMs)) {
            // no download after last call, compensate for delay between calls
            let delay = 0.001 * (nowMs - bolaState.lastCallTimeMs);
            bolaState.placeholderBuffer += Math.max(0, delay);
        }

        bolaState.lastCallTimeMs = nowMs;
        bolaState.lastSegmentStart = NaN;
        bolaState.lastSegmentRequestTimeMs = NaN;
        bolaState.lastSegmentFinishTimeMs = NaN;

        checkBolaStateStableBufferTime(bolaState, mediaType);
    }

    function onBufferEmpty() {
        // if we rebuffer, we don't want the placeholder buffer to artificially raise BOLA quality
        for (let mediaType in bolaStateDict) {
            if (bolaStateDict.hasOwnProperty(mediaType) && bolaStateDict[mediaType].state === BOLA_STATE_STEADY) {
                bolaStateDict[mediaType].placeholderBuffer = 0;
            }
        }
    }

    function onPlaybackSeeking() {
        // TODO: 1. Verify what happens if we seek mid-fragment.
        // TODO: 2. If e.g. we have 10s fragments and seek, we might want to download the first fragment at a lower quality to restart playback quickly.
        for (let mediaType in bolaStateDict) {
            if (bolaStateDict.hasOwnProperty(mediaType)) {
                let bolaState = bolaStateDict[mediaType];
                if (bolaState.state !== BOLA_STATE_ONE_BITRATE) {
                    bolaState.state = BOLA_STATE_STARTUP; // TODO: BOLA_STATE_SEEK?
                    clearBolaStateOnSeek(bolaState);
                }
            }
        }
    }

    function onPeriodSwitchStarted() {
        // TODO: does this have to be handled here?
    }

    function onMediaFragmentLoaded(e) {
        if (e && e.chunk && e.chunk.mediaInfo) {
            let bolaState = bolaStateDict[e.chunk.mediaInfo.type];
            if (bolaState && bolaState.state !== BOLA_STATE_ONE_BITRATE) {
                let start = e.chunk.start;
                if (isNaN(bolaState.mostAdvancedSegmentStart) || start > bolaState.mostAdvancedSegmentStart) {
                    bolaState.mostAdvancedSegmentStart = start;
                    bolaState.lastSegmentWasReplacement = false;
                } else {
                    bolaState.lastSegmentWasReplacement = true;
                }

                bolaState.lastSegmentStart = start;
                bolaState.lastSegmentDurationS = e.chunk.duration;
                bolaState.lastQuality = e.chunk.quality;

                checkNewSegment(bolaState, e.chunk.mediaInfo.type);
            }
        }
    }

    function onMetricAdded(e) {
        if (e && e.metric === MetricsConstants.HTTP_REQUEST && e.value && e.value.type === HTTPRequest.MEDIA_SEGMENT_TYPE && e.value.trace && e.value.trace.length) {
            let bolaState = bolaStateDict[e.mediaType];
            if (bolaState && bolaState.state !== BOLA_STATE_ONE_BITRATE) {
                bolaState.lastSegmentRequestTimeMs = e.value.trequest.getTime();
                bolaState.lastSegmentFinishTimeMs = e.value._tfinish.getTime();

                checkNewSegment(bolaState, e.mediaType);
            }
        }
    }

    /*
     * When a new segment is downloaded, we get two notifications: onMediaFragmentLoaded() and onMetricAdded(). It is
     * possible that the quality for the downloaded segment was lower (not higher) than the quality indicated by BOLA.
     * This might happen because of other rules such as the DroppedFramesRule. When this happens, we trim the
     * placeholder buffer to make BOLA more stable. This mechanism also avoids inflating the buffer when BOLA itself
     * decides not to increase the quality to avoid oscillations.
     *
     * We should also check for replacement segments (fast switching). In this case, a segment is downloaded but does
     * not grow the actual buffer. Fast switching might cause the buffer to deplete, causing BOLA to drop the bitrate.
     * We avoid this by growing the placeholder buffer.
     */
    function checkNewSegment(bolaState, mediaType) {
        if (!isNaN(bolaState.lastSegmentStart) && !isNaN(bolaState.lastSegmentRequestTimeMs) && !isNaN(bolaState.placeholderBuffer)) {
            bolaState.placeholderBuffer *= PLACEHOLDER_BUFFER_DECAY;

            // Find what maximum buffer corresponding to last segment was, and ensure placeholder is not relatively larger.
            if (!isNaN(bolaState.lastSegmentFinishTimeMs)) {
                let bufferLevel = dashMetrics.getCurrentBufferLevel(metricsModel.getReadOnlyMetricsFor(mediaType));
                let bufferAtLastSegmentRequest = bufferLevel + 0.001 * (bolaState.lastSegmentFinishTimeMs - bolaState.lastSegmentRequestTimeMs); // estimate
                let maxEffectiveBufferForLastSegment = maxBufferLevelForQuality(bolaState, bolaState.lastQuality);
                let maxPlaceholderBuffer = Math.max(0, maxEffectiveBufferForLastSegment - bufferAtLastSegmentRequest);
                bolaState.placeholderBuffer = Math.min(maxPlaceholderBuffer, bolaState.placeholderBuffer);
            }

            // then see if we should grow placeholder buffer

            if (bolaState.lastSegmentWasReplacement && !isNaN(bolaState.lastSegmentDurationS)) {
                // compensate for segments that were downloaded but did not grow the buffer
                bolaState.placeholderBuffer += bolaState.lastSegmentDurationS;
            }

            bolaState.lastSegmentStart = NaN;
            bolaState.lastSegmentRequestTimeMs = NaN;
        }
    }

    function onQualityChangeRequested(e) {
        // Useful to store change requests when abandoning a download.
        if (e) {
            const bolaState = bolaStateDict[e.mediaType];
            if (bolaState && bolaState.state !== BOLA_STATE_ONE_BITRATE) {
                bolaState.abrQuality = e.newQuality;
            }
        }
    }

    function onFragmentLoadingAbandoned(e) {
        if (e) {
            const bolaState = bolaStateDict[e.mediaType];
            if (bolaState && bolaState.state !== BOLA_STATE_ONE_BITRATE) {
                // deflate placeholderBuffer - note that we want to be conservative when abandoning
                const bufferLevel = dashMetrics.getCurrentBufferLevel(metricsModel.getReadOnlyMetricsFor(e.mediaType));
                let wantEffectiveBufferLevel;
                if (bolaState.abrQuality > 0) {
                    // deflate to point where BOLA just chooses newQuality over newQuality-1
                    wantEffectiveBufferLevel = minBufferLevelForQuality(bolaState, bolaState.abrQuality);
                } else {
                    wantEffectiveBufferLevel = MINIMUM_BUFFER_S;
                }
                const maxPlaceholderBuffer = Math.max(0, wantEffectiveBufferLevel - bufferLevel);
                bolaState.placeholderBuffer = Math.min(bolaState.placeholderBuffer, maxPlaceholderBuffer);
            }
        }
    }

    function getMaxIndex(rulesContext) {
        const mediaInfo = rulesContext.getMediaInfo();
        const mediaType = rulesContext.getMediaType();
        const metrics = metricsModel.getReadOnlyMetricsFor(mediaType);
        const streamProcessor = rulesContext.getStreamProcessor();
        const streamInfo = rulesContext.getStreamInfo();
        const abrController = rulesContext.getAbrController();
        const throughputHistory = abrController.getThroughputHistory();
        const streamId = streamInfo ? streamInfo.id : null;
        const isDynamic = streamInfo && streamInfo.manifestInfo && streamInfo.manifestInfo.isDynamic;
        const useBufferOccupancyABR = rulesContext.useBufferOccupancyABR();
        const switchRequest = SwitchRequest(context).create();
        switchRequest.reason = switchRequest.reason || {};

        if (!useBufferOccupancyABR) {
            return switchRequest;
        }

        streamProcessor.getScheduleController().setTimeToLoadDelay(0);

        let bolaState = getBolaState(rulesContext);

        if (bolaState.state === BOLA_STATE_ONE_BITRATE) {
            // shouldn't even have been called
            log('BOLA ABR rule invoked for media type \'' + mediaType + '\' with only one bitrate.');
            return switchRequest;
        }

        let bufferLevel = dashMetrics.getCurrentBufferLevel(metrics);
        let throughput = throughputHistory.getAverageThroughput(mediaType, isDynamic);
        let safeThroughput = throughputHistory.getSafeAverageThroughput(mediaType, isDynamic);
        let latency = throughputHistory.getAverageLatency(mediaType);
        let quality;

        switchRequest.reason.state = bolaState.state;
        switchRequest.reason.throughput = throughput;
        switchRequest.reason.latency = latency;

        if (isNaN(throughput)) { // isNaN(throughput) === isNaN(safeThroughput) === isNaN(latency)
            // still starting up - not enough information
            return switchRequest;
        }

        switch (bolaState.state) {
            case BOLA_STATE_STARTUP:
                quality = abrController.getQualityForBitrate(mediaInfo, safeThroughput, latency);

                switchRequest.quality = quality;
                switchRequest.reason.throughput = safeThroughput;

                bolaState.placeholderBuffer = Math.max(0, minBufferLevelForQuality(bolaState, quality) - bufferLevel);
                bolaState.lastQuality = quality;

                if (!isNaN(bolaState.lastSegmentDurationS) && bufferLevel >= bolaState.lastSegmentDurationS) {
                    bolaState.state = BOLA_STATE_STEADY;
                }

                break; // BOLA_STATE_STARTUP

            case BOLA_STATE_STEADY:

                // NB: The placeholder buffer is added to bufferLevel to come up with a bitrate.
                //     This might lead BOLA to be too optimistic and to choose a bitrate that would lead to rebuffering -
                //     if the real buffer bufferLevel runs out, the placeholder buffer cannot prevent rebuffering.
                //     However, the InsufficientBufferRule takes care of this scenario.

                updatePlaceholderBuffer(bolaState, mediaType);

                quality = getQualityFromBufferLevel(bolaState, bufferLevel + bolaState.placeholderBuffer);

                // we want to avoid oscillations
                // We implement the "BOLA-O" variant: when network bandwidth lies between two encoded bitrate levels, stick to the lowest level.
                let qualityForThroughput = abrController.getQualityForBitrate(mediaInfo, safeThroughput, latency);
                if (quality > bolaState.lastQuality && quality > qualityForThroughput) {
                    // only intervene if we are trying to *increase* quality to an *unsustainable* level
                    // we are only avoid oscillations - do not drop below last quality

                    quality = Math.max(qualityForThroughput, bolaState.lastQuality);
                }

                // We do not want to overfill buffer with low quality chunks.
                // Note that there will be no delay if buffer level is below MINIMUM_BUFFER_S, probably even with some margin higher than MINIMUM_BUFFER_S.
                let delayS = Math.max(0, bufferLevel + bolaState.placeholderBuffer - maxBufferLevelForQuality(bolaState, quality));

                // First reduce placeholder buffer, then tell schedule controller to pause.
                if (delayS <= bolaState.placeholderBuffer) {
                    bolaState.placeholderBuffer -= delayS;
                    delayS = 0;
                } else {
                    delayS -= bolaState.placeholderBuffer;
                    bolaState.placeholderBuffer = 0;

                    if (quality < abrController.getTopQualityIndexFor(mediaType, streamId)) {
                        // At top quality, allow schedule controller to decide how far to fill buffer.
                        streamProcessor.getScheduleController().setTimeToLoadDelay(1000 * delayS);
                    } else {
                        delayS = 0;
                    }
                }

                switchRequest.quality = quality;
                switchRequest.reason.throughput = throughput;
                switchRequest.reason.latency = latency;
                switchRequest.reason.bufferLevel = bufferLevel;
                switchRequest.reason.placeholderBuffer = bolaState.placeholderBuffer;
                switchRequest.reason.delay = delayS;

                bolaState.lastQuality = quality;
                // keep bolaState.state === BOLA_STATE_STEADY

                break; // BOLA_STATE_STEADY

            default:
                log('BOLA ABR rule invoked in bad state.');
                // should not arrive here, try to recover
                switchRequest.quality = abrController.getQualityForBitrate(mediaInfo, safeThroughput, latency);
                switchRequest.reason.state = bolaState.state;
                switchRequest.reason.throughput = safeThroughput;
                switchRequest.reason.latency = latency;
                bolaState.state = BOLA_STATE_STARTUP;
                clearBolaStateOnSeek(bolaState);
        }

        return switchRequest;
    }

    function resetInitialSettings() {
        bolaStateDict = {};
    }

    function reset() {
        resetInitialSettings();

        eventBus.off(Events.BUFFER_EMPTY, onBufferEmpty, instance);
        eventBus.off(Events.PLAYBACK_SEEKING, onPlaybackSeeking, instance);
        eventBus.off(Events.PERIOD_SWITCH_STARTED, onPeriodSwitchStarted, instance);
        eventBus.off(Events.MEDIA_FRAGMENT_LOADED, onMediaFragmentLoaded, instance);
        eventBus.off(Events.METRIC_ADDED, onMetricAdded, instance);
        eventBus.off(Events.QUALITY_CHANGE_REQUESTED, onQualityChangeRequested, instance);
        eventBus.off(Events.FRAGMENT_LOADING_ABANDONED, onFragmentLoadingAbandoned, instance);
    }

    instance = {
        getMaxIndex: getMaxIndex,
        reset: reset
    };

    setup();
    return instance;
}

BolaRule.__dashjs_factory_name = 'BolaRule';
export default FactoryMaker.getClassFactory(BolaRule);