Source: lib/media/streaming_engine.js

  1. /*! @license
  2.  * Shaka Player
  3.  * Copyright 2016 Google LLC
  4.  * SPDX-License-Identifier: Apache-2.0
  5.  */
  7. /**
  8.  * @fileoverview
  9.  * @suppress {missingRequire} TODO(b/152540451): this shouldn't be needed
  10.  */
  12. goog.provide('shaka.media.StreamingEngine');
  14. goog.require('goog.asserts');
  15. goog.require('shaka.log');
  16. goog.require('shaka.media.InitSegmentReference');
  17. goog.require('shaka.media.MediaSourceEngine');
  18. goog.require('shaka.media.SegmentIterator');
  19. goog.require('shaka.media.SegmentReference');
  20. goog.require('shaka.net.Backoff');
  21. goog.require('shaka.net.NetworkingEngine');
  22. goog.require('shaka.util.DelayedTick');
  23. goog.require('shaka.util.Destroyer');
  24. goog.require('shaka.util.Error');
  25. goog.require('shaka.util.FakeEvent');
  26. goog.require('shaka.util.IDestroyable');
  27. goog.require('shaka.util.ManifestParserUtils');
  28. goog.require('shaka.util.MimeUtils');
  29. goog.require('shaka.util.Mp4Parser');
  30. goog.require('shaka.util.Networking');
  33. /**
  34.  * @summary Creates a Streaming Engine.
  35.  * The StreamingEngine is responsible for setting up the Manifest's Streams
  36.  * (i.e., for calling each Stream's createSegmentIndex() function), for
  37.  * downloading segments, for co-ordinating audio, video, and text buffering.
  38.  * The StreamingEngine provides an interface to switch between Streams, but it
  39.  * does not choose which Streams to switch to.
  40.  *
  41.  * The StreamingEngine does not need to be notified about changes to the
  42.  * Manifest's SegmentIndexes; however, it does need to be notified when new
  43.  * Variants are added to the Manifest.
  44.  *
  45.  * To start the StreamingEngine the owner must first call configure(), followed
  46.  * by one call to switchVariant(), one optional call to switchTextStream(), and
  47.  * finally a call to start().  After start() resolves, switch*() can be used
  48.  * freely.
  49.  *
  50.  * The owner must call seeked() each time the playhead moves to a new location
  51.  * within the presentation timeline; however, the owner may forego calling
  52.  * seeked() when the playhead moves outside the presentation timeline.
  53.  *
  54.  * @implements {shaka.util.IDestroyable}
  55.  */
  56. shaka.media.StreamingEngine = class {
  57.   /**
  58.    * @param {shaka.extern.Manifest} manifest
  59.    * @param {shaka.media.StreamingEngine.PlayerInterface} playerInterface
  60.    */
  61.   constructor(manifest, playerInterface) {
  62.     /** @private {?shaka.media.StreamingEngine.PlayerInterface} */
  63.     this.playerInterface_ = playerInterface;
  65.     /** @private {?shaka.extern.Manifest} */
  66.     this.manifest_ = manifest;
  68.     /** @private {?shaka.extern.StreamingConfiguration} */
  69.     this.config_ = null;
  71.     /** @private {number} */
  72.     this.bufferingGoalScale_ = 1;
  74.     /** @private {?shaka.extern.Variant} */
  75.     this.currentVariant_ = null;
  77.     /** @private {?shaka.extern.Stream} */
  78.     this.currentTextStream_ = null;
  80.     /**
  81.      * Maps a content type, e.g., 'audio', 'video', or 'text', to a MediaState.
  82.      *
  83.      * @private {!Map.<shaka.util.ManifestParserUtils.ContentType,
  84.      *                 !shaka.media.StreamingEngine.MediaState_>}
  85.      */
  86.     this.mediaStates_ = new Map();
  88.     /**
  89.      * Set to true once the initial media states have been created.
  90.      *
  91.      * @private {boolean}
  92.      */
  93.     this.startupComplete_ = false;
  95.     /**
  96.      * Used for delay and backoff of failure callbacks, so that apps do not
  97.      * retry instantly.
  98.      *
  99.      * @private {shaka.net.Backoff}
  100.      */
  101.     this.failureCallbackBackoff_ = null;
  103.     /**
  104.      * Set to true on fatal error.  Interrupts fetchAndAppend_().
  105.      *
  106.      * @private {boolean}
  107.      */
  108.     this.fatalError_ = false;
  110.     /** @private {!shaka.util.Destroyer} */
  111.     this.destroyer_ = new shaka.util.Destroyer(() => this.doDestroy_());
  112.   }
  114.   /** @override */
  115.   destroy() {
  116.     return this.destroyer_.destroy();
  117.   }
  119.   /**
  120.    * @return {!Promise}
  121.    * @private
  122.    */
  123.   async doDestroy_() {
  124.     const aborts = [];
  126.     for (const state of this.mediaStates_.values()) {
  127.       this.cancelUpdate_(state);
  128.       aborts.push(this.abortOperations_(state));
  129.     }
  131.     await Promise.all(aborts);
  133.     this.mediaStates_.clear();
  135.     this.playerInterface_ = null;
  136.     this.manifest_ = null;
  137.     this.config_ = null;
  138.   }
  140.   /**
  141.    * Called by the Player to provide an updated configuration any time it
  142.    * changes. Must be called at least once before start().
  143.    *
  144.    * @param {shaka.extern.StreamingConfiguration} config
  145.    */
  146.   configure(config) {
  147.     this.config_ = config;
  149.     // Create separate parameters for backoff during streaming failure.
  151.     /** @type {shaka.extern.RetryParameters} */
  152.     const failureRetryParams = {
  153.       // The term "attempts" includes the initial attempt, plus all retries.
  154.       // In order to see a delay, there would have to be at least 2 attempts.
  155.       maxAttempts: Math.max(config.retryParameters.maxAttempts, 2),
  156.       baseDelay: config.retryParameters.baseDelay,
  157.       backoffFactor: config.retryParameters.backoffFactor,
  158.       fuzzFactor: config.retryParameters.fuzzFactor,
  159.       timeout: 0,  // irrelevant
  160.       stallTimeout: 0, // irrelevant
  161.       connectionTimeout: 0, // irrelevant
  162.     };
  164.     // We don't want to ever run out of attempts.  The application should be
  165.     // allowed to retry streaming infinitely if it wishes.
  166.     const autoReset = true;
  167.     this.failureCallbackBackoff_ =
  168.         new shaka.net.Backoff(failureRetryParams, autoReset);
  169.   }
  172.   /**
  173.    * Initialize and start streaming.
  174.    *
  175.    * By calling this method, StreamingEngine will start streaming the variant
  176.    * chosen by a prior call to switchVariant(), and optionally, the text stream
  177.    * chosen by a prior call to switchTextStream().  Once the Promise resolves,
  178.    * switch*() may be called freely.
  179.    *
  180.    * @return {!Promise}
  181.    */
  182.   async start() {
  183.     goog.asserts.assert(this.config_,
  184.         'StreamingEngine configure() must be called before init()!');
  186.     // Setup the initial set of Streams and then begin each update cycle.
  187.     await this.initStreams_();
  188.     this.destroyer_.ensureNotDestroyed();
  190.     shaka.log.debug('init: completed initial Stream setup');
  191.     this.startupComplete_ = true;
  192.   }
  194.   /**
  195.    * Get the current variant we are streaming.  Returns null if nothing is
  196.    * streaming.
  197.    * @return {?shaka.extern.Variant}
  198.    */
  199.   getCurrentVariant() {
  200.     return this.currentVariant_;
  201.   }
  203.   /**
  204.    * Get the text stream we are streaming.  Returns null if there is no text
  205.    * streaming.
  206.    * @return {?shaka.extern.Stream}
  207.    */
  208.   getCurrentTextStream() {
  209.     return this.currentTextStream_;
  210.   }
  212.   /**
  213.    * Start streaming text, creating a new media state.
  214.    *
  215.    * @param {shaka.extern.Stream} stream
  216.    * @return {!Promise}
  217.    * @private
  218.    */
  219.   async loadNewTextStream_(stream) {
  220.     const ContentType = shaka.util.ManifestParserUtils.ContentType;
  221.     goog.asserts.assert(!this.mediaStates_.has(ContentType.TEXT),
  222.         'Should not call loadNewTextStream_ while streaming text!');
  224.     try {
  225.       // Clear MediaSource's buffered text, so that the new text stream will
  226.       // properly replace the old buffered text.
  227.       // TODO: Should this happen in unloadTextStream() instead?
  228.       await this.playerInterface_.mediaSourceEngine.clear(ContentType.TEXT);
  229.     } catch (error) {
  230.       if (this.playerInterface_) {
  231.         this.playerInterface_.onError(error);
  232.       }
  233.     }
  235.     const mimeType = shaka.util.MimeUtils.getFullType(
  236.         stream.mimeType, stream.codecs);
  237.     this.playerInterface_.mediaSourceEngine.reinitText(mimeType);
  239.     const textDisplayer =
  240.         this.playerInterface_.mediaSourceEngine.getTextDisplayer();
  241.     const streamText =
  242.         textDisplayer.isTextVisible() || this.config_.alwaysStreamText;
  244.     if (streamText) {
  245.       const state = this.createMediaState_(stream);
  246.       this.mediaStates_.set(ContentType.TEXT, state);
  247.       this.scheduleUpdate_(state, 0);
  248.     }
  249.   }
  252.   /**
  253.    * Stop fetching text stream when the user chooses to hide the captions.
  254.    */
  255.   unloadTextStream() {
  256.     const ContentType = shaka.util.ManifestParserUtils.ContentType;
  258.     const state = this.mediaStates_.get(ContentType.TEXT);
  259.     if (state) {
  260.       this.cancelUpdate_(state);
  261.       this.abortOperations_(state).catch(() => {});
  262.       this.mediaStates_.delete(ContentType.TEXT);
  263.     }
  264.     this.currentTextStream_ = null;
  265.   }
  267.   /**
  268.    * Set trick play on or off.
  269.    * If trick play is on, related trick play streams will be used when possible.
  270.    * @param {boolean} on
  271.    */
  272.   setTrickPlay(on) {
  273.     const ContentType = shaka.util.ManifestParserUtils.ContentType;
  275.     const mediaState = this.mediaStates_.get(ContentType.VIDEO);
  276.     if (!mediaState) {
  277.       return;
  278.     }
  280.     const stream = mediaState.stream;
  281.     if (!stream) {
  282.       return;
  283.     }
  285.     shaka.log.debug('setTrickPlay', on);
  286.     if (on) {
  287.       const trickModeVideo = stream.trickModeVideo;
  288.       if (!trickModeVideo) {
  289.         return;  // Can't engage trick play.
  290.       }
  292.       const normalVideo = mediaState.restoreStreamAfterTrickPlay;
  293.       if (normalVideo) {
  294.         return;  // Already in trick play.
  295.       }
  297.       shaka.log.debug('Engaging trick mode stream', trickModeVideo);
  298.       this.switchInternal_(trickModeVideo, /* clearBuffer= */ false,
  299.           /* safeMargin= */ 0, /* force= */ false);
  301.       mediaState.restoreStreamAfterTrickPlay = stream;
  302.     } else {
  303.       const normalVideo = mediaState.restoreStreamAfterTrickPlay;
  304.       if (!normalVideo) {
  305.         return;
  306.       }
  308.       shaka.log.debug('Restoring non-trick-mode stream', normalVideo);
  309.       mediaState.restoreStreamAfterTrickPlay = null;
  310.       this.switchInternal_(normalVideo, /* clearBuffer= */ true,
  311.           /* safeMargin= */ 0, /* force= */ false);
  312.     }
  313.   }
  316.   /**
  317.    * @param {shaka.extern.Variant} variant
  318.    * @param {boolean=} clearBuffer
  319.    * @param {number=} safeMargin
  320.    * @param {boolean=} force
  321.    *   If true, reload the variant even if it did not change.
  322.    */
  323.   switchVariant(variant, clearBuffer = false, safeMargin = 0, force = false) {
  324.     this.currentVariant_ = variant;
  326.     if (!this.startupComplete_) {
  327.       // The selected variant will be used in start().
  328.       return;
  329.     }
  331.     if (variant.video) {
  332.       this.switchInternal_(
  333.           variant.video, /* clearBuffer= */ clearBuffer,
  334.           /* safeMargin= */ safeMargin, /* force= */ force);
  335.     }
  336.     if (variant.audio) {
  337.       this.switchInternal_(
  338.           variant.audio, /* clearBuffer= */ clearBuffer,
  339.           /* safeMargin= */ safeMargin, /* force= */ force);
  340.     }
  341.   }
  344.   /**
  345.    * @param {shaka.extern.Stream} textStream
  346.    */
  347.   switchTextStream(textStream) {
  348.     this.currentTextStream_ = textStream;
  350.     if (!this.startupComplete_) {
  351.       // The selected text stream will be used in start().
  352.       return;
  353.     }
  355.     const ContentType = shaka.util.ManifestParserUtils.ContentType;
  356.     goog.asserts.assert(textStream && textStream.type == ContentType.TEXT,
  357.         'Wrong stream type passed to switchTextStream!');
  359.     this.switchInternal_(
  360.         textStream, /* clearBuffer= */ true,
  361.         /* safeMargin= */ 0, /* force= */ false);
  362.   }
  365.   /** Reload the current text stream. */
  366.   reloadTextStream() {
  367.     const ContentType = shaka.util.ManifestParserUtils.ContentType;
  368.     const mediaState = this.mediaStates_.get(ContentType.TEXT);
  369.     if (mediaState) { // Don't reload if there's no text to begin with.
  370.       this.switchInternal_(
  371.           mediaState.stream, /* clearBuffer= */ true,
  372.           /* safeMargin= */ 0, /* force= */ true);
  373.     }
  374.   }
  377.   /**
  378.    * Switches to the given Stream. |stream| may be from any Variant.
  379.    *
  380.    * @param {shaka.extern.Stream} stream
  381.    * @param {boolean} clearBuffer
  382.    * @param {number} safeMargin
  383.    * @param {boolean} force
  384.    *   If true, reload the text stream even if it did not change.
  385.    * @private
  386.    */
  387.   switchInternal_(stream, clearBuffer, safeMargin, force) {
  388.     const ContentType = shaka.util.ManifestParserUtils.ContentType;
  389.     const type = /** @type {!ContentType} */(stream.type);
  390.     const mediaState = this.mediaStates_.get(type);
  392.     if (!mediaState && stream.type == ContentType.TEXT) {
  393.       this.loadNewTextStream_(stream);
  394.       return;
  395.     }
  397.     goog.asserts.assert(mediaState, 'switch: expected mediaState to exist');
  398.     if (!mediaState) {
  399.       return;
  400.     }
  402.     if (mediaState.restoreStreamAfterTrickPlay) {
  403.       shaka.log.debug('switch during trick play mode', stream);
  405.       // Already in trick play mode, so stick with trick mode tracks if
  406.       // possible.
  407.       if (stream.trickModeVideo) {
  408.         // Use the trick mode stream, but revert to the new selection later.
  409.         mediaState.restoreStreamAfterTrickPlay = stream;
  410.         stream = stream.trickModeVideo;
  411.         shaka.log.debug('switch found trick play stream', stream);
  412.       } else {
  413.         // There is no special trick mode video for this stream!
  414.         mediaState.restoreStreamAfterTrickPlay = null;
  415.         shaka.log.debug('switch found no special trick play stream');
  416.       }
  417.     }
  419.     if (mediaState.stream == stream && !force) {
  420.       const streamTag = shaka.media.StreamingEngine.logPrefix_(mediaState);
  421.       shaka.log.debug('switch: Stream ' + streamTag + ' already active');
  422.       return;
  423.     }
  425.     if (stream.type == ContentType.TEXT) {
  426.       // Mime types are allowed to change for text streams.
  427.       // Reinitialize the text parser, but only if we are going to fetch the
  428.       // init segment again.
  429.       const fullMimeType = shaka.util.MimeUtils.getFullType(
  430.           stream.mimeType, stream.codecs);
  431.       this.playerInterface_.mediaSourceEngine.reinitText(fullMimeType);
  432.     }
  434.     // Releases the segmentIndex of the old stream.
  435.     if (mediaState.stream.closeSegmentIndex) {
  436.       mediaState.stream.closeSegmentIndex();
  437.     }
  439.     mediaState.stream = stream;
  440.     mediaState.segmentIterator = null;
  442.     const streamTag = shaka.media.StreamingEngine.logPrefix_(mediaState);
  443.     shaka.log.debug('switch: switching to Stream ' + streamTag);
  445.     if (clearBuffer) {
  446.       if (mediaState.clearingBuffer) {
  447.         // We are already going to clear the buffer, but make sure it is also
  448.         // flushed.
  449.         mediaState.waitingToFlushBuffer = true;
  450.       } else if (mediaState.performingUpdate) {
  451.         // We are performing an update, so we have to wait until it's finished.
  452.         // onUpdate_() will call clearBuffer_() when the update has finished.
  453.         // We need to save the safe margin because its value will be needed when
  454.         // clearing the buffer after the update.
  455.         mediaState.waitingToClearBuffer = true;
  456.         mediaState.clearBufferSafeMargin = safeMargin;
  457.         mediaState.waitingToFlushBuffer = true;
  458.       } else {
  459.         // Cancel the update timer, if any.
  460.         this.cancelUpdate_(mediaState);
  461.         // Clear right away.
  462.         this.clearBuffer_(mediaState, /* flush= */ true, safeMargin)
  463.             .catch((error) => {
  464.               if (this.playerInterface_) {
  465.                 goog.asserts.assert(error instanceof shaka.util.Error,
  466.                     'Wrong error type!');
  467.                 this.playerInterface_.onError(error);
  468.               }
  469.             });
  470.       }
  471.     }
  473.     this.makeAbortDecision_(mediaState).catch((error) => {
  474.       if (this.playerInterface_) {
  475.         goog.asserts.assert(error instanceof shaka.util.Error,
  476.             'Wrong error type!');
  477.         this.playerInterface_.onError(error);
  478.       }
  479.     });
  480.   }
  483.   /**
  484.    * Decide if it makes sense to abort the current operation, and abort it if
  485.    * so.
  486.    *
  487.    * @param {!shaka.media.StreamingEngine.MediaState_} mediaState
  488.    * @private
  489.    */
  490.   async makeAbortDecision_(mediaState) {
  491.     // If the operation is completed, it will be set to null, and there's no
  492.     // need to abort the request.
  493.     if (!mediaState.operation) {
  494.       return;
  495.     }
  497.     const originalStream = mediaState.stream;
  498.     const originalOperation = mediaState.operation;
  500.     if (!originalStream.segmentIndex) {
  501.       // Create the new segment index so the time taken is accounted for when
  502.       // deciding whether to abort.
  503.       await originalStream.createSegmentIndex();
  504.     }
  506.     if (mediaState.operation != originalOperation) {
  507.       // The original operation completed while we were getting a segment index,
  508.       // so there's nothing to do now.
  509.       return;
  510.     }
  512.     if (mediaState.stream != originalStream) {
  513.       // The stream changed again while we were getting a segment index.  We
  514.       // can't carry out this check, since another one might be in progress by
  515.       // now.
  516.       return;
  517.     }
  519.     goog.asserts.assert(mediaState.stream.segmentIndex,
  520.         'Segment index should exist by now!');
  522.     if (this.shouldAbortCurrentRequest_(mediaState)) {
  523.       shaka.log.info('Aborting current segment request.');
  524.       mediaState.operation.abort();
  525.     }
  526.   }
  528.   /**
  529.    * Returns whether we should abort the current request.
  530.    *
  531.    * @param {!shaka.media.StreamingEngine.MediaState_} mediaState
  532.    * @return {boolean}
  533.    * @private
  534.    */
  535.   shouldAbortCurrentRequest_(mediaState) {
  536.     goog.asserts.assert(mediaState.operation,
  537.         'Abort logic requires an ongoing operation!');
  538.     goog.asserts.assert(mediaState.stream && mediaState.stream.segmentIndex,
  539.         'Abort logic requires a segment index');
  541.     const presentationTime = this.playerInterface_.getPresentationTime();
  542.     const bufferEnd =
  543.         this.playerInterface_.mediaSourceEngine.bufferEnd(mediaState.type);
  545.     // The next segment to append from the current stream.  This doesn't
  546.     // account for a pending network request and will likely be different from
  547.     // that since we just switched.
  548.     const timeNeeded = this.getTimeNeeded_(mediaState, presentationTime);
  549.     const index = mediaState.stream.segmentIndex.find(timeNeeded);
  550.     const newSegment =
  551.         index == null ? null : mediaState.stream.segmentIndex.get(index);
  553.     let newSegmentSize = newSegment ? newSegment.getSize() : null;
  554.     if (newSegment && !newSegmentSize) {
  555.       // compute approximate segment size using stream bandwidth
  556.       const duration = newSegment.getEndTime() - newSegment.getStartTime();
  557.       const bandwidth = mediaState.stream.bandwidth || 0;
  558.       // bandwidth is in bits per second, and the size is in bytes
  559.       newSegmentSize = duration * bandwidth / 8;
  560.     }
  562.     if (!newSegmentSize) {
  563.       return false;
  564.     }
  566.     // When switching, we'll need to download the init segment.
  567.     const init = newSegment.initSegmentReference;
  568.     if (init) {
  569.       newSegmentSize += init.getSize() || 0;
  570.     }
  572.     const bandwidthEstimate = this.playerInterface_.getBandwidthEstimate();
  574.     // The estimate is in bits per second, and the size is in bytes.  The time
  575.     // remaining is in seconds after this calculation.
  576.     const timeToFetchNewSegment = (newSegmentSize * 8) / bandwidthEstimate;
  578.     // If the new segment can be finished in time without risking a buffer
  579.     // underflow, we should abort the old one and switch.
  580.     const bufferedAhead = (bufferEnd || 0) - presentationTime;
  581.     const safetyBuffer = Math.max(
  582.         this.manifest_.minBufferTime || 0,
  583.         this.config_.rebufferingGoal);
  584.     const safeBufferedAhead = bufferedAhead - safetyBuffer;
  585.     if (timeToFetchNewSegment < safeBufferedAhead) {
  586.       return true;
  587.     }
  589.     // If the thing we want to switch to will be done more quickly than what
  590.     // we've got in progress, we should abort the old one and switch.
  591.     const bytesRemaining = mediaState.operation.getBytesRemaining();
  592.     if (bytesRemaining > newSegmentSize) {
  593.       return true;
  594.     }
  596.     // Otherwise, complete the operation in progress.
  597.     return false;
  598.   }
  601.   /**
  602.    * Notifies the StreamingEngine that the playhead has moved to a valid time
  603.    * within the presentation timeline.
  604.    */
  605.   seeked() {
  606.     const presentationTime = this.playerInterface_.getPresentationTime();
  607.     const smallGapLimit = this.config_.smallGapLimit;
  608.     const ContentType = shaka.util.ManifestParserUtils.ContentType;
  609.     const newTimeIsBuffered = (type) => {
  610.       return this.playerInterface_.mediaSourceEngine.isBuffered(
  611.           type, presentationTime, smallGapLimit);
  612.     };
  614.     let streamCleared = false;
  615.     for (const type of this.mediaStates_.keys()) {
  616.       const mediaState = this.mediaStates_.get(type);
  617.       const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  619.       // Always clear the iterator since we need to start streaming from the
  620.       // new time.  This also happens in clearBuffer_, but if we don't clear,
  621.       // we still want to reset the iterator.
  622.       mediaState.segmentIterator = null;
  624.       if (!newTimeIsBuffered(type)) {
  625.         const bufferEnd =
  626.             this.playerInterface_.mediaSourceEngine.bufferEnd(type);
  627.         const somethingBuffered = bufferEnd != null;
  629.         // Don't clear the buffer unless something is buffered.  This extra
  630.         // check prevents extra, useless calls to clear the buffer.
  631.         if (somethingBuffered || mediaState.performingUpdate) {
  632.           this.forceClearBuffer_(mediaState);
  633.           streamCleared = true;
  634.         }
  636.         // If there is an operation in progress, stop it now.
  637.         if (mediaState.operation) {
  638.           mediaState.operation.abort();
  639.           shaka.log.debug(logPrefix, 'Aborting operation due to seek');
  640.           mediaState.operation = null;
  641.         }
  643.         // The pts has shifted from the seek, invalidating captions currently
  644.         // in the text buffer. Thus, clear and reset the caption parser.
  645.         if (type === ContentType.TEXT) {
  646.           this.playerInterface_.mediaSourceEngine.resetCaptionParser();
  647.         }
  648.       }
  649.     }
  651.     if (!streamCleared) {
  652.       shaka.log.debug(
  653.           '(all): seeked: buffered seek: presentationTime=' + presentationTime);
  654.     }
  655.   }
  658.   /**
  659.    * Clear the buffer for a given stream.  Unlike clearBuffer_, this will handle
  660.    * cases where a MediaState is performing an update.  After this runs, every
  661.    * MediaState will have a pending update.
  662.    * @param {!shaka.media.StreamingEngine.MediaState_} mediaState
  663.    * @private
  664.    */
  665.   forceClearBuffer_(mediaState) {
  666.     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  668.     if (mediaState.clearingBuffer) {
  669.       // We're already clearing the buffer, so we don't need to clear the
  670.       // buffer again.
  671.       shaka.log.debug(logPrefix, 'clear: already clearing the buffer');
  672.       return;
  673.     }
  675.     if (mediaState.waitingToClearBuffer) {
  676.       // May not be performing an update, but an update will still happen.
  677.       // See: https://github.com/shaka-project/shaka-player/issues/334
  678.       shaka.log.debug(logPrefix, 'clear: already waiting');
  679.       return;
  680.     }
  682.     if (mediaState.performingUpdate) {
  683.       // We are performing an update, so we have to wait until it's finished.
  684.       // onUpdate_() will call clearBuffer_() when the update has finished.
  685.       shaka.log.debug(logPrefix, 'clear: currently updating');
  686.       mediaState.waitingToClearBuffer = true;
  687.       // We can set the offset to zero to remember that this was a call to
  688.       // clearAllBuffers.
  689.       mediaState.clearBufferSafeMargin = 0;
  690.       return;
  691.     }
  693.     const type = mediaState.type;
  694.     if (this.playerInterface_.mediaSourceEngine.bufferStart(type) == null) {
  695.       // Nothing buffered.
  696.       shaka.log.debug(logPrefix, 'clear: nothing buffered');
  697.       if (mediaState.updateTimer == null) {
  698.         // Note: an update cycle stops when we buffer to the end of the
  699.         // presentation, or when we raise an error.
  700.         this.scheduleUpdate_(mediaState, 0);
  701.       }
  702.       return;
  703.     }
  705.     // An update may be scheduled, but we can just cancel it and clear the
  706.     // buffer right away. Note: clearBuffer_() will schedule the next update.
  707.     shaka.log.debug(logPrefix, 'clear: handling right now');
  708.     this.cancelUpdate_(mediaState);
  709.     this.clearBuffer_(mediaState, /* flush= */ false, 0).catch((error) => {
  710.       if (this.playerInterface_) {
  711.         goog.asserts.assert(error instanceof shaka.util.Error,
  712.             'Wrong error type!');
  713.         this.playerInterface_.onError(error);
  714.       }
  715.     });
  716.   }
  719.   /**
  720.    * Initializes the initial streams and media states.  This will schedule
  721.    * updates for the given types.
  722.    *
  723.    * @return {!Promise}
  724.    * @private
  725.    */
  726.   async initStreams_() {
  727.     const ContentType = shaka.util.ManifestParserUtils.ContentType;
  729.     goog.asserts.assert(this.config_,
  730.         'StreamingEngine configure() must be called before init()!');
  732.     if (!this.currentVariant_) {
  733.       shaka.log.error('init: no Streams chosen');
  734.       throw new shaka.util.Error(
  735.           shaka.util.Error.Severity.CRITICAL,
  736.           shaka.util.Error.Category.STREAMING,
  737.           shaka.util.Error.Code.STREAMING_ENGINE_STARTUP_INVALID_STATE);
  738.     }
  740.     /**
  741.      * @type {!Map.<shaka.util.ManifestParserUtils.ContentType,
  742.      *              shaka.extern.Stream>}
  743.      */
  744.     const streamsByType = new Map();
  745.     /** @type {!Set.<shaka.extern.Stream>} */
  746.     const streams = new Set();
  748.     if (this.currentVariant_.audio) {
  749.       streamsByType.set(ContentType.AUDIO, this.currentVariant_.audio);
  750.       streams.add(this.currentVariant_.audio);
  751.     }
  753.     if (this.currentVariant_.video) {
  754.       streamsByType.set(ContentType.VIDEO, this.currentVariant_.video);
  755.       streams.add(this.currentVariant_.video);
  756.     }
  758.     if (this.currentTextStream_) {
  759.       streamsByType.set(ContentType.TEXT, this.currentTextStream_);
  760.       streams.add(this.currentTextStream_);
  761.     }
  763.     // Init MediaSourceEngine.
  764.     const mediaSourceEngine = this.playerInterface_.mediaSourceEngine;
  765.     const forceTransmuxTS = this.config_.forceTransmuxTS;
  767.     await mediaSourceEngine.init(streamsByType, forceTransmuxTS);
  768.     this.destroyer_.ensureNotDestroyed();
  770.     this.setDuration_();
  772.     for (const type of streamsByType.keys()) {
  773.       const stream = streamsByType.get(type);
  774.       if (!this.mediaStates_.has(type)) {
  775.         const state = this.createMediaState_(stream);
  776.         this.mediaStates_.set(type, state);
  777.         this.scheduleUpdate_(state, 0);
  778.       }
  779.     }
  780.   }
  783.   /**
  784.    * Creates a media state.
  785.    *
  786.    * @param {shaka.extern.Stream} stream
  787.    * @return {shaka.media.StreamingEngine.MediaState_}
  788.    * @private
  789.    */
  790.   createMediaState_(stream) {
  791.     return /** @type {shaka.media.StreamingEngine.MediaState_} */ ({
  792.       stream,
  793.       type: stream.type,
  794.       segmentIterator: null,
  795.       lastSegmentReference: null,
  796.       lastInitSegmentReference: null,
  797.       lastTimestampOffset: null,
  798.       lastAppendWindowStart: null,
  799.       lastAppendWindowEnd: null,
  800.       restoreStreamAfterTrickPlay: null,
  801.       endOfStream: false,
  802.       performingUpdate: false,
  803.       updateTimer: null,
  804.       waitingToClearBuffer: false,
  805.       clearBufferSafeMargin: 0,
  806.       waitingToFlushBuffer: false,
  807.       clearingBuffer: false,
  808.       recovering: false,
  809.       hasError: false,
  810.       operation: null,
  811.     });
  812.   }
  815.   /**
  816.    * Sets the MediaSource's duration.
  817.    * @private
  818.    */
  819.   setDuration_() {
  820.     const duration = this.manifest_.presentationTimeline.getDuration();
  821.     if (duration < Infinity) {
  822.       this.playerInterface_.mediaSourceEngine.setDuration(duration);
  823.     } else {
  824.       // Not all platforms support infinite durations, so set a finite duration
  825.       // so we can append segments and so the user agent can seek.
  826.       this.playerInterface_.mediaSourceEngine.setDuration(Math.pow(2, 32));
  827.     }
  828.   }
  831.   /**
  832.    * Called when |mediaState|'s update timer has expired.
  833.    *
  834.    * @param {!shaka.media.StreamingEngine.MediaState_} mediaState
  835.    * @suppress {suspiciousCode} The compiler assumes that updateTimer can't
  836.    *   change during the await, and so complains about the null check.
  837.    * @private
  838.    */
  839.   async onUpdate_(mediaState) {
  840.     this.destroyer_.ensureNotDestroyed();
  842.     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  844.     // Sanity check.
  845.     goog.asserts.assert(
  846.         !mediaState.performingUpdate && (mediaState.updateTimer != null),
  847.         logPrefix + ' unexpected call to onUpdate_()');
  848.     if (mediaState.performingUpdate || (mediaState.updateTimer == null)) {
  849.       return;
  850.     }
  852.     goog.asserts.assert(
  853.         !mediaState.clearingBuffer, logPrefix +
  854.         ' onUpdate_() should not be called when clearing the buffer');
  855.     if (mediaState.clearingBuffer) {
  856.       return;
  857.     }
  859.     mediaState.updateTimer = null;
  861.     // Handle pending buffer clears.
  862.     if (mediaState.waitingToClearBuffer) {
  863.       // Note: clearBuffer_() will schedule the next update.
  864.       shaka.log.debug(logPrefix, 'skipping update and clearing the buffer');
  865.       await this.clearBuffer_(
  866.           mediaState, mediaState.waitingToFlushBuffer,
  867.           mediaState.clearBufferSafeMargin);
  868.       return;
  869.     }
  871.     // Make sure the segment index exists. If not, create the segment index.
  872.     if (!mediaState.stream.segmentIndex) {
  873.       const thisStream = mediaState.stream;
  875.       await mediaState.stream.createSegmentIndex();
  877.       if (thisStream != mediaState.stream) {
  878.         // We switched streams while in the middle of this async call to
  879.         // createSegmentIndex.  Abandon this update and schedule a new one if
  880.         // there's not already one pending.
  881.         // Releases the segmentIndex of the old stream.
  882.         if (thisStream.closeSegmentIndex) {
  883.           goog.asserts.assert(!mediaState.stream.segmentIndex,
  884.               'mediastate.stream should not have segmentIndex yet.');
  885.           thisStream.closeSegmentIndex();
  886.         }
  887.         if (mediaState.updateTimer == null) {
  888.           this.scheduleUpdate_(mediaState, 0);
  889.         }
  890.         return;
  891.       }
  892.     }
  894.     // Update the MediaState.
  895.     try {
  896.       const delay = this.update_(mediaState);
  897.       if (delay != null) {
  898.         this.scheduleUpdate_(mediaState, delay);
  899.         mediaState.hasError = false;
  900.       }
  901.     } catch (error) {
  902.       await this.handleStreamingError_(error);
  903.       return;
  904.     }
  906.     const mediaStates = Array.from(this.mediaStates_.values());
  908.     // Check if we've buffered to the end of the presentation.  We delay adding
  909.     // the audio and video media states, so it is possible for the text stream
  910.     // to be the only state and buffer to the end.  So we need to wait until we
  911.     // have completed startup to determine if we have reached the end.
  912.     if (this.startupComplete_ &&
  913.         mediaStates.every((ms) => ms.endOfStream)) {
  914.       shaka.log.v1(logPrefix, 'calling endOfStream()...');
  915.       await this.playerInterface_.mediaSourceEngine.endOfStream();
  916.       this.destroyer_.ensureNotDestroyed();
  918.       // If the media segments don't reach the end, then we need to update the
  919.       // timeline duration to match the final media duration to avoid
  920.       // buffering forever at the end.
  921.       // We should only do this if the duration needs to shrink.
  922.       // Growing it by less than 1ms can actually cause buffering on
  923.       // replay, as in https://github.com/shaka-project/shaka-player/issues/979
  924.       // On some platforms, this can spuriously be 0, so ignore this case.
  925.       // https://github.com/shaka-project/shaka-player/issues/1967,
  926.       const duration = this.playerInterface_.mediaSourceEngine.getDuration();
  927.       if (duration != 0 &&
  928.           duration < this.manifest_.presentationTimeline.getDuration()) {
  929.         this.manifest_.presentationTimeline.setDuration(duration);
  930.       }
  931.     }
  932.   }
  935.   /**
  936.    * Updates the given MediaState.
  937.    *
  938.    * @param {shaka.media.StreamingEngine.MediaState_} mediaState
  939.    * @return {?number} The number of seconds to wait until updating again or
  940.    *   null if another update does not need to be scheduled.
  941.    * @private
  942.    */
  943.   update_(mediaState) {
  944.     goog.asserts.assert(this.manifest_, 'manifest_ should not be null');
  945.     goog.asserts.assert(this.config_, 'config_ should not be null');
  947.     const ContentType = shaka.util.ManifestParserUtils.ContentType;
  949.     // Do not schedule update for closed captions text mediastate, since closed
  950.     // captions are embedded in video streams.
  951.     if (shaka.media.StreamingEngine.isEmbeddedText_(mediaState)) {
  952.       this.playerInterface_.mediaSourceEngine.setSelectedClosedCaptionId(
  953.           mediaState.stream.originalId || '');
  954.       return null;
  955.     } else if (mediaState.type == ContentType.TEXT) {
  956.       // Disable embedded captions if not desired (e.g. if transitioning from
  957.       // embedded to not-embedded captions).
  958.       this.playerInterface_.mediaSourceEngine.clearSelectedClosedCaptionId();
  959.     }
  961.     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  963.     // Compute how far we've buffered ahead of the playhead.
  964.     const presentationTime = this.playerInterface_.getPresentationTime();
  966.     // Get the next timestamp we need.
  967.     const timeNeeded = this.getTimeNeeded_(mediaState, presentationTime);
  968.     shaka.log.v2(logPrefix, 'timeNeeded=' + timeNeeded);
  970.     // Get the amount of content we have buffered, accounting for drift.  This
  971.     // is only used to determine if we have meet the buffering goal.  This
  972.     // should be the same method that PlayheadObserver uses.
  973.     const bufferedAhead =
  974.         this.playerInterface_.mediaSourceEngine.bufferedAheadOf(
  975.             mediaState.type, presentationTime);
  977.     shaka.log.v2(logPrefix,
  978.         'update_:',
  979.         'presentationTime=' + presentationTime,
  980.         'bufferedAhead=' + bufferedAhead);
  982.     const unscaledBufferingGoal = Math.max(
  983.         this.manifest_.minBufferTime || 0,
  984.         this.config_.rebufferingGoal,
  985.         this.config_.bufferingGoal);
  987.     const scaledBufferingGoal =
  988.         unscaledBufferingGoal * this.bufferingGoalScale_;
  990.     // Check if we've buffered to the end of the presentation.
  991.     const timeUntilEnd =
  992.         this.manifest_.presentationTimeline.getDuration() - timeNeeded;
  993.     const oneMicrosecond = 1e-6;
  994.     if (timeUntilEnd < oneMicrosecond) {
  995.       // We shouldn't rebuffer if the playhead is close to the end of the
  996.       // presentation.
  997.       shaka.log.debug(logPrefix, 'buffered to end of presentation');
  998.       mediaState.endOfStream = true;
  1000.       if (mediaState.type == ContentType.VIDEO) {
  1001.         // Since the text stream of CEA closed captions doesn't have update
  1002.         // timer, we have to set the text endOfStream based on the video
  1003.         // stream's endOfStream state.
  1004.         const textState = this.mediaStates_.get(ContentType.TEXT);
  1005.         if (textState &&
  1006.             shaka.media.StreamingEngine.isEmbeddedText_(textState)) {
  1007.           textState.endOfStream = true;
  1008.         }
  1009.       }
  1010.       return null;
  1011.     }
  1012.     mediaState.endOfStream = false;
  1014.     // If we've buffered to the buffering goal then schedule an update.
  1015.     if (bufferedAhead >= scaledBufferingGoal) {
  1016.       shaka.log.v2(logPrefix, 'buffering goal met');
  1018.       // Do not try to predict the next update.  Just poll according to
  1019.       // configuration (seconds). The playback rate can change at any time, so
  1020.       // any prediction we make now could be terribly invalid soon.
  1021.       return this.config_.updateIntervalSeconds / 2;
  1022.     }
  1024.     const bufferEnd =
  1025.         this.playerInterface_.mediaSourceEngine.bufferEnd(mediaState.type);
  1026.     const reference = this.getSegmentReferenceNeeded_(
  1027.         mediaState, presentationTime, bufferEnd);
  1028.     if (!reference) {
  1029.       // The segment could not be found, does not exist, or is not available.
  1030.       // In any case just try again... if the manifest is incomplete or is not
  1031.       // being updated then we'll idle forever; otherwise, we'll end up getting
  1032.       // a SegmentReference eventually.
  1033.       return this.config_.updateIntervalSeconds;
  1034.     }
  1036.     // Do not let any one stream get far ahead of any other.
  1037.     let minTimeNeeded = Infinity;
  1038.     const mediaStates = Array.from(this.mediaStates_.values());
  1039.     for (const otherState of mediaStates) {
  1040.       // Do not consider embedded captions in this calculation.  It could lead
  1041.       // to hangs in streaming.
  1042.       if (shaka.media.StreamingEngine.isEmbeddedText_(otherState)) {
  1043.         continue;
  1044.       }
  1045.       // If there is no next segment, ignore this stream.  This happens with
  1046.       // text when there's a Period with no text in it.
  1047.       if (otherState.segmentIterator && !otherState.segmentIterator.current()) {
  1048.         continue;
  1049.       }
  1051.       const timeNeeded = this.getTimeNeeded_(otherState, presentationTime);
  1052.       minTimeNeeded = Math.min(minTimeNeeded, timeNeeded);
  1053.     }
  1055.     const maxSegmentDuration =
  1056.         this.manifest_.presentationTimeline.getMaxSegmentDuration();
  1057.     const maxRunAhead = maxSegmentDuration *
  1058.         shaka.media.StreamingEngine.MAX_RUN_AHEAD_SEGMENTS_;
  1059.     if (timeNeeded >= minTimeNeeded + maxRunAhead) {
  1060.       // Wait and give other media types time to catch up to this one.
  1061.       // For example, let video buffering catch up to audio buffering before
  1062.       // fetching another audio segment.
  1063.       shaka.log.v2(logPrefix, 'waiting for other streams to buffer');
  1064.       return this.config_.updateIntervalSeconds;
  1065.     }
  1067.     const p = this.fetchAndAppend_(mediaState, presentationTime, reference);
  1068.     p.catch(() => {});  // TODO(#1993): Handle asynchronous errors.
  1069.     return null;
  1070.   }
  1073.   /**
  1074.    * Gets the next timestamp needed. Returns the playhead's position if the
  1075.    * buffer is empty; otherwise, returns the time at which the last segment
  1076.    * appended ends.
  1077.    *
  1078.    * @param {shaka.media.StreamingEngine.MediaState_} mediaState
  1079.    * @param {number} presentationTime
  1080.    * @return {number} The next timestamp needed.
  1081.    * @private
  1082.    */
  1083.   getTimeNeeded_(mediaState, presentationTime) {
  1084.     // Get the next timestamp we need. We must use |lastSegmentReference|
  1085.     // to determine this and not the actual buffer for two reasons:
  1086.     //   1. Actual segments end slightly before their advertised end times, so
  1087.     //      the next timestamp we need is actually larger than |bufferEnd|.
  1088.     //   2. There may be drift (the timestamps in the segments are ahead/behind
  1089.     //      of the timestamps in the manifest), but we need drift-free times
  1090.     //      when comparing times against the presentation timeline.
  1091.     if (!mediaState.lastSegmentReference) {
  1092.       return presentationTime;
  1093.     }
  1095.     return mediaState.lastSegmentReference.endTime;
  1096.   }
  1099.   /**
  1100.    * Gets the SegmentReference of the next segment needed.
  1101.    *
  1102.    * @param {shaka.media.StreamingEngine.MediaState_} mediaState
  1103.    * @param {number} presentationTime
  1104.    * @param {?number} bufferEnd
  1105.    * @return {shaka.media.SegmentReference} The SegmentReference of the
  1106.    *   next segment needed. Returns null if a segment could not be found, does
  1107.    *   not exist, or is not available.
  1108.    * @private
  1109.    */
  1110.   getSegmentReferenceNeeded_(mediaState, presentationTime, bufferEnd) {
  1111.     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  1112.     goog.asserts.assert(
  1113.         mediaState.stream.segmentIndex,
  1114.         'segment index should have been generated already');
  1116.     if (mediaState.segmentIterator) {
  1117.       // Something is buffered from the same Stream.  Use the current position
  1118.       // in the segment index.  This is updated via next() after each segment is
  1119.       // appended.
  1120.       return mediaState.segmentIterator.current();
  1121.     } else if (mediaState.lastSegmentReference || bufferEnd) {
  1122.       // Something is buffered from another Stream.
  1123.       const time = mediaState.lastSegmentReference ?
  1124.           mediaState.lastSegmentReference.endTime :
  1125.           bufferEnd;
  1126.       goog.asserts.assert(time != null, 'Should have a time to search');
  1127.       shaka.log.v1(
  1128.           logPrefix, 'looking up segment from new stream endTime:', time);
  1130.       mediaState.segmentIterator =
  1131.           mediaState.stream.segmentIndex.getIteratorForTime(time);
  1132.       const ref = mediaState.segmentIterator &&
  1133.           mediaState.segmentIterator.next().value;
  1134.       if (ref == null) {
  1135.         shaka.log.warning(logPrefix, 'cannot find segment', 'endTime:', time);
  1136.       }
  1137.       return ref;
  1138.     } else {
  1139.       // Nothing is buffered.  Start at the playhead time.
  1141.       // If there's positive drift then we need to adjust the lookup time, and
  1142.       // may wind up requesting the previous segment to be safe.
  1143.       // inaccurateManifestTolerance should be 0 for low latency streaming.
  1144.       const inaccurateTolerance = this.config_.inaccurateManifestTolerance;
  1145.       const lookupTime = Math.max(presentationTime - inaccurateTolerance, 0);
  1147.       shaka.log.v1(logPrefix, 'looking up segment',
  1148.           'lookupTime:', lookupTime,
  1149.           'presentationTime:', presentationTime);
  1151.       let ref = null;
  1152.       if (inaccurateTolerance) {
  1153.         mediaState.segmentIterator =
  1154.             mediaState.stream.segmentIndex.getIteratorForTime(lookupTime);
  1155.         ref = mediaState.segmentIterator &&
  1156.             mediaState.segmentIterator.next().value;
  1157.       }
  1158.       if (!ref) {
  1159.         // If we can't find a valid segment with the drifted time, look for a
  1160.         // segment with the presentation time.
  1161.         mediaState.segmentIterator =
  1162.             mediaState.stream.segmentIndex.getIteratorForTime(presentationTime);
  1163.         ref = mediaState.segmentIterator &&
  1164.             mediaState.segmentIterator.next().value;
  1165.       }
  1166.       if (ref == null) {
  1167.         shaka.log.warning(logPrefix, 'cannot find segment',
  1168.             'lookupTime:', lookupTime,
  1169.             'presentationTime:', presentationTime);
  1170.       }
  1171.       return ref;
  1172.     }
  1173.   }
  1176.   /**
  1177.    * Fetches and appends the given segment. Sets up the given MediaState's
  1178.    * associated SourceBuffer and evicts segments if either are required
  1179.    * beforehand. Schedules another update after completing successfully.
  1180.    *
  1181.    * @param {!shaka.media.StreamingEngine.MediaState_} mediaState
  1182.    * @param {number} presentationTime
  1183.    * @param {!shaka.media.SegmentReference} reference
  1184.    * @private
  1185.    */
  1186.   async fetchAndAppend_(mediaState, presentationTime, reference) {
  1187.     const ContentType = shaka.util.ManifestParserUtils.ContentType;
  1188.     const StreamingEngine = shaka.media.StreamingEngine;
  1189.     const logPrefix = StreamingEngine.logPrefix_(mediaState);
  1191.     shaka.log.v1(logPrefix,
  1192.         'fetchAndAppend_:',
  1193.         'presentationTime=' + presentationTime,
  1194.         'reference.startTime=' + reference.startTime,
  1195.         'reference.endTime=' + reference.endTime);
  1197.     // Subtlety: The playhead may move while asynchronous update operations are
  1198.     // in progress, so we should avoid calling playhead.getTime() in any
  1199.     // callbacks. Furthermore, switch() or seeked() may be called at any time,
  1200.     // so we store the old iterator.  This allows the mediaState to change and
  1201.     // we'll update the old iterator.
  1202.     const stream = mediaState.stream;
  1203.     const iter = mediaState.segmentIterator;
  1205.     mediaState.performingUpdate = true;
  1207.     try {
  1208.       await this.initSourceBuffer_(mediaState, reference);
  1209.       this.destroyer_.ensureNotDestroyed();
  1210.       if (this.fatalError_) {
  1211.         return;
  1212.       }
  1214.       shaka.log.v2(logPrefix, 'fetching segment');
  1215.       const isMP4 = stream.mimeType == 'video/mp4' ||
  1216.               stream.mimeType == 'audio/mp4';
  1217.       const isReadableStreamSupported = window.ReadableStream;
  1218.       // Enable MP4 low latency streaming with ReadableStream chunked data.
  1219.       if (this.config_.lowLatencyMode && isReadableStreamSupported && isMP4) {
  1220.         let remaining = new Uint8Array(0);
  1221.         const streamDataCallback = async (data) => {
  1222.           this.destroyer_.ensureNotDestroyed();
  1223.           if (this.fatalError_) {
  1224.             return;
  1225.           }
  1226.           // Append the data with complete boxes.
  1227.           // Every time streamDataCallback gets called, append the new data to
  1228.           // the remaining data.
  1229.           // Find the last fully completed Mdat box, and slice the data into two
  1230.           // parts: the first part with completed Mdat boxes, and the second
  1231.           // part with an incomplete box.
  1232.           // Append the first part, and save the second part as remaining data,
  1233.           // and handle it with the next streamDataCallback call.
  1234.           remaining = this.concatArray_(remaining, data);
  1235.           let sawMDAT = false;
  1236.           let offset = 0;
  1237.           new shaka.util.Mp4Parser()
  1238.               .box('mdat', (box) => {
  1239.                 offset = box.size + box.start;
  1240.                 sawMDAT = true;
  1241.               })
  1242.               .parse(remaining, /* partialOkay= */ false,
  1243.                   /* isChunkedData= */ true);
  1244.           if (sawMDAT) {
  1245.             const dataToAppend = remaining.subarray(0, offset);
  1246.             remaining = remaining.subarray(offset);
  1247.             await this.append_(
  1248.                 mediaState, presentationTime, stream, reference, dataToAppend);
  1249.           }
  1250.         };
  1252.         await this.fetch_(mediaState, reference, streamDataCallback);
  1253.       } else {
  1254.         if (this.config_.lowLatencyMode && !isReadableStreamSupported) {
  1255.           shaka.log.warning('Low latency streaming mode is enabled, but ' +
  1256.             'ReadableStream is not supported by the browser.');
  1257.         }
  1258.         const fetchSegment = this.fetch_(mediaState, reference);
  1259.         const result = await fetchSegment;
  1260.         this.destroyer_.ensureNotDestroyed();
  1261.         if (this.fatalError_) {
  1262.           return;
  1263.         }
  1265.         // If the text stream gets switched between fetch_() and append_(), the
  1266.         // new text parser is initialized, but the new init segment is not
  1267.         // fetched yet.  That would cause an error in TextParser.parseMedia().
  1268.         // See http://b/168253400
  1269.         if (mediaState.waitingToClearBuffer) {
  1270.           shaka.log.info(logPrefix, 'waitingToClearBuffer, skip append');
  1271.           mediaState.performingUpdate = false;
  1272.           this.scheduleUpdate_(mediaState, 0);
  1273.           return;
  1274.         }
  1275.         await this.append_(
  1276.             mediaState, presentationTime, stream, reference, result);
  1277.       }
  1279.       this.destroyer_.ensureNotDestroyed();
  1280.       if (this.fatalError_) {
  1281.         return;
  1282.       }
  1283.       // move to next segment after appending the current segment.
  1284.       mediaState.lastSegmentReference = reference;
  1285.       const newRef = iter.next().value;
  1286.       shaka.log.v2(logPrefix, 'advancing to next segment', newRef);
  1288.       mediaState.performingUpdate = false;
  1289.       mediaState.recovering = false;
  1291.       const info = this.playerInterface_.mediaSourceEngine.getBufferedInfo();
  1292.       const buffered = info[mediaState.type];
  1293.       // Convert the buffered object to a string capture its properties on
  1294.       // WebOS.
  1295.       shaka.log.v1(logPrefix, 'finished fetch and append',
  1296.           JSON.stringify(buffered));
  1298.       if (!mediaState.waitingToClearBuffer) {
  1299.         this.playerInterface_.onSegmentAppended();
  1300.       }
  1302.       // Update right away.
  1303.       this.scheduleUpdate_(mediaState, 0);
  1304.     } catch (error) {
  1305.       this.destroyer_.ensureNotDestroyed(error);
  1306.       if (this.fatalError_) {
  1307.         return;
  1308.       }
  1309.       goog.asserts.assert(error instanceof shaka.util.Error,
  1310.           'Should only receive a Shaka error');
  1312.       mediaState.performingUpdate = false;
  1314.       if (error.code == shaka.util.Error.Code.OPERATION_ABORTED) {
  1315.         // If the network slows down, abort the current fetch request and start
  1316.         // a new one, and ignore the error message.
  1317.         mediaState.performingUpdate = false;
  1318.         mediaState.updateTimer = null;
  1319.         this.scheduleUpdate_(mediaState, 0);
  1320.       } else if (mediaState.type == ContentType.TEXT &&
  1321.           this.config_.ignoreTextStreamFailures) {
  1322.         if (error.code == shaka.util.Error.Code.BAD_HTTP_STATUS) {
  1323.           shaka.log.warning(logPrefix,
  1324.               'Text stream failed to download. Proceeding without it.');
  1325.         } else {
  1326.           shaka.log.warning(logPrefix,
  1327.               'Text stream failed to parse. Proceeding without it.');
  1328.         }
  1329.         this.mediaStates_.delete(ContentType.TEXT);
  1330.       } else if (error.code == shaka.util.Error.Code.QUOTA_EXCEEDED_ERROR) {
  1331.         this.handleQuotaExceeded_(mediaState, error);
  1332.       } else if (error.code == shaka.util.Error.Code.BAD_HTTP_STATUS &&
  1333.           error.data && error.data[1] == 404) {
  1334.         // The segment could not be found, does not exist, or is not available.
  1335.         // In any case just try again.
  1336.         // The current segment is not available. Schedule another update to
  1337.         // fetch the segment again.
  1338.         shaka.log.v2(logPrefix, 'segment not available.');
  1339.         mediaState.performingUpdate = false;
  1340.         mediaState.updateTimer = null;
  1341.         this.scheduleUpdate_(mediaState, 1);
  1342.       } else {
  1343.         shaka.log.error(logPrefix, 'failed fetch and append: code=' +
  1344.             error.code);
  1345.         mediaState.hasError = true;
  1347.         error.severity = shaka.util.Error.Severity.CRITICAL;
  1348.         await this.handleStreamingError_(error);
  1349.       }
  1350.     }
  1351.   }
  1354.   /**
  1355.    * Clear per-stream error states and retry any failed streams.
  1356.    * @return {boolean} False if unable to retry.
  1357.    */
  1358.   retry() {
  1359.     if (this.destroyer_.destroyed()) {
  1360.       shaka.log.error('Unable to retry after StreamingEngine is destroyed!');
  1361.       return false;
  1362.     }
  1364.     if (this.fatalError_) {
  1365.       shaka.log.error('Unable to retry after StreamingEngine encountered a ' +
  1366.                       'fatal error!');
  1367.       return false;
  1368.     }
  1370.     for (const mediaState of this.mediaStates_.values()) {
  1371.       const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  1372.       if (mediaState.hasError) {
  1373.         shaka.log.info(logPrefix, 'Retrying after failure...');
  1374.         mediaState.hasError = false;
  1375.         this.scheduleUpdate_(mediaState, 0.1);
  1376.       }
  1377.     }
  1379.     return true;
  1380.   }
  1383.   /**
  1384.    * Append the data to the remaining data.
  1385.    * @param {!Uint8Array} remaining
  1386.    * @param {!Uint8Array} data
  1387.    * @return {!Uint8Array}
  1388.    * @private
  1389.    */
  1390.   concatArray_(remaining, data) {
  1391.     const result = new Uint8Array(remaining.length + data.length);
  1392.     result.set(remaining);
  1393.     result.set(data, remaining.length);
  1394.     return result;
  1395.   }
  1398.   /**
  1399.    * Handles a QUOTA_EXCEEDED_ERROR.
  1400.    *
  1401.    * @param {shaka.media.StreamingEngine.MediaState_} mediaState
  1402.    * @param {!shaka.util.Error} error
  1403.    * @private
  1404.    */
  1405.   handleQuotaExceeded_(mediaState, error) {
  1406.     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  1408.     // The segment cannot fit into the SourceBuffer. Ideally, MediaSource would
  1409.     // have evicted old data to accommodate the segment; however, it may have
  1410.     // failed to do this if the segment is very large, or if it could not find
  1411.     // a suitable time range to remove.
  1412.     //
  1413.     // We can overcome the latter by trying to append the segment again;
  1414.     // however, to avoid continuous QuotaExceededErrors we must reduce the size
  1415.     // of the buffer going forward.
  1416.     //
  1417.     // If we've recently reduced the buffering goals, wait until the stream
  1418.     // which caused the first QuotaExceededError recovers. Doing this ensures
  1419.     // we don't reduce the buffering goals too quickly.
  1421.     const mediaStates = Array.from(this.mediaStates_.values());
  1422.     const waitingForAnotherStreamToRecover = mediaStates.some((ms) => {
  1423.       return ms != mediaState && ms.recovering;
  1424.     });
  1426.     if (!waitingForAnotherStreamToRecover) {
  1427.       // Reduction schedule: 80%, 60%, 40%, 20%, 16%, 12%, 8%, 4%, fail.
  1428.       // Note: percentages are used for comparisons to avoid rounding errors.
  1429.       const percentBefore = Math.round(100 * this.bufferingGoalScale_);
  1430.       if (percentBefore > 20) {
  1431.         this.bufferingGoalScale_ -= 0.2;
  1432.       } else if (percentBefore > 4) {
  1433.         this.bufferingGoalScale_ -= 0.04;
  1434.       } else {
  1435.         shaka.log.error(
  1436.             logPrefix, 'MediaSource threw QuotaExceededError too many times');
  1437.         mediaState.hasError = true;
  1438.         this.fatalError_ = true;
  1439.         this.playerInterface_.onError(error);
  1440.         return;
  1441.       }
  1442.       const percentAfter = Math.round(100 * this.bufferingGoalScale_);
  1443.       shaka.log.warning(
  1444.           logPrefix,
  1445.           'MediaSource threw QuotaExceededError:',
  1446.           'reducing buffering goals by ' + (100 - percentAfter) + '%');
  1447.       mediaState.recovering = true;
  1448.     } else {
  1449.       shaka.log.debug(
  1450.           logPrefix,
  1451.           'MediaSource threw QuotaExceededError:',
  1452.           'waiting for another stream to recover...');
  1453.     }
  1455.     // QuotaExceededError gets thrown if evication didn't help to make room
  1456.     // for a segment. We want to wait for a while (4 seconds is just an
  1457.     // arbitrary number) before updating to give the playhead a chance to
  1458.     // advance, so we don't immidiately throw again.
  1459.     this.scheduleUpdate_(mediaState, 4);
  1460.   }
  1463.   /**
  1464.    * Sets the given MediaState's associated SourceBuffer's timestamp offset,
  1465.    * append window, and init segment if they have changed. If an error occurs
  1466.    * then neither the timestamp offset or init segment are unset, since another
  1467.    * call to switch() will end up superseding them.
  1468.    *
  1469.    * @param {shaka.media.StreamingEngine.MediaState_} mediaState
  1470.    * @param {!shaka.media.SegmentReference} reference
  1471.    * @return {!Promise}
  1472.    * @private
  1473.    */
  1474.   async initSourceBuffer_(mediaState, reference) {
  1475.     const StreamingEngine = shaka.media.StreamingEngine;
  1476.     const logPrefix = StreamingEngine.logPrefix_(mediaState);
  1478.     /** @type {!Array.<!Promise>} */
  1479.     const operations = [];
  1481.     // Rounding issues can cause us to remove the first frame of a Period, so
  1482.     // reduce the window start time slightly.
  1483.     const appendWindowStart = Math.max(0,
  1484.         reference.appendWindowStart -
  1485.         StreamingEngine.APPEND_WINDOW_START_FUDGE_);
  1486.     const appendWindowEnd =
  1487.         reference.appendWindowEnd + StreamingEngine.APPEND_WINDOW_END_FUDGE_;
  1489.     goog.asserts.assert(
  1490.         reference.startTime <= appendWindowEnd,
  1491.         logPrefix + ' segment should start before append window end');
  1493.     const timestampOffset = reference.timestampOffset;
  1494.     if (timestampOffset != mediaState.lastTimestampOffset ||
  1495.         appendWindowStart != mediaState.lastAppendWindowStart ||
  1496.         appendWindowEnd != mediaState.lastAppendWindowEnd) {
  1497.       shaka.log.v1(logPrefix, 'setting timestamp offset to ' + timestampOffset);
  1498.       shaka.log.v1(logPrefix,
  1499.           'setting append window start to ' + appendWindowStart);
  1500.       shaka.log.v1(logPrefix,
  1501.           'setting append window end to ' + appendWindowEnd);
  1503.       const setProperties = async () => {
  1504.         try {
  1505.           mediaState.lastAppendWindowStart = appendWindowStart;
  1506.           mediaState.lastAppendWindowEnd = appendWindowEnd;
  1507.           mediaState.lastTimestampOffset = timestampOffset;
  1509.           await this.playerInterface_.mediaSourceEngine.setStreamProperties(
  1510.               mediaState.type, timestampOffset, appendWindowStart,
  1511.               appendWindowEnd);
  1512.         } catch (error) {
  1513.           mediaState.lastAppendWindowStart = null;
  1514.           mediaState.lastAppendWindowEnd = null;
  1515.           mediaState.lastTimestampOffset = null;
  1517.           throw error;
  1518.         }
  1519.       };
  1520.       operations.push(setProperties());
  1521.     }
  1523.     if (!shaka.media.InitSegmentReference.equal(
  1524.         reference.initSegmentReference, mediaState.lastInitSegmentReference)) {
  1525.       mediaState.lastInitSegmentReference = reference.initSegmentReference;
  1527.       if (reference.initSegmentReference) {
  1528.         shaka.log.v1(logPrefix, 'fetching init segment');
  1530.         const fetchInit =
  1531.             this.fetch_(mediaState, reference.initSegmentReference);
  1532.         const append = async () => {
  1533.           try {
  1534.             const initSegment = await fetchInit;
  1535.             this.destroyer_.ensureNotDestroyed();
  1536.             shaka.log.v1(logPrefix, 'appending init segment');
  1537.             const hasClosedCaptions = mediaState.stream.closedCaptions &&
  1538.                 mediaState.stream.closedCaptions.size > 0;
  1539.             await this.playerInterface_.mediaSourceEngine.appendBuffer(
  1540.                 mediaState.type, initSegment, /* startTime= */ null,
  1541.                 /* endTime= */ null, hasClosedCaptions);
  1542.           } catch (error) {
  1543.             mediaState.lastInitSegmentReference = null;
  1544.             throw error;
  1545.           }
  1546.         };
  1547.         this.playerInterface_.onInitSegmentAppended(
  1548.             reference.startTime, reference.initSegmentReference);
  1549.         operations.push(append());
  1550.       }
  1551.     }
  1553.     await Promise.all(operations);
  1554.   }
  1557.   /**
  1558.    * Appends the given segment and evicts content if required to append.
  1559.    *
  1560.    * @param {!shaka.media.StreamingEngine.MediaState_} mediaState
  1561.    * @param {number} presentationTime
  1562.    * @param {shaka.extern.Stream} stream
  1563.    * @param {!shaka.media.SegmentReference} reference
  1564.    * @param {BufferSource} segment
  1565.    * @return {!Promise}
  1566.    * @private
  1567.    */
  1568.   async append_(mediaState, presentationTime, stream, reference,
  1569.       segment) {
  1570.     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  1572.     const hasClosedCaptions = stream.closedCaptions &&
  1573.         stream.closedCaptions.size > 0;
  1574.     if ((stream.emsgSchemeIdUris != null &&
  1575.         stream.emsgSchemeIdUris.length > 0) ||
  1576.         this.config_.dispatchAllEmsgBoxes) {
  1577.       new shaka.util.Mp4Parser()
  1578.           .fullBox(
  1579.               'emsg',
  1580.               (box) => this.parseEMSG_(
  1581.                   reference, stream.emsgSchemeIdUris, box))
  1582.           .parse(segment);
  1583.     }
  1585.     await this.evict_(mediaState, presentationTime);
  1586.     this.destroyer_.ensureNotDestroyed();
  1587.     shaka.log.v1(logPrefix, 'appending media segment');
  1589.     await this.playerInterface_.mediaSourceEngine.appendBuffer(
  1590.         mediaState.type,
  1591.         segment,
  1592.         reference.startTime,
  1593.         reference.endTime,
  1594.         hasClosedCaptions);
  1595.     this.destroyer_.ensureNotDestroyed();
  1596.     shaka.log.v2(logPrefix, 'appended media segment');
  1597.   }
  1600.   /**
  1601.    * Parse the EMSG box from a MP4 container.
  1602.    *
  1603.    * @param {!shaka.media.SegmentReference} reference
  1604.    * @param {?Array.<string>} emsgSchemeIdUris Array of emsg
  1605.    *     scheme_id_uri for which emsg boxes should be parsed.
  1606.    * @param {!shaka.extern.ParsedBox} box
  1607.    * @private
  1608.    * https://dashif-documents.azurewebsites.net/Events/master/event.html#emsg-format
  1609.    * aligned(8) class DASHEventMessageBox
  1610.    *    extends FullBox(‘emsg’, version, flags = 0){
  1611.    * if (version==0) {
  1612.    *   string scheme_id_uri;
  1613.    *   string value;
  1614.    *   unsigned int(32) timescale;
  1615.    *   unsigned int(32) presentation_time_delta;
  1616.    *   unsigned int(32) event_duration;
  1617.    *   unsigned int(32) id;
  1618.    * } else if (version==1) {
  1619.    *   unsigned int(32) timescale;
  1620.    *   unsigned int(64) presentation_time;
  1621.    *   unsigned int(32) event_duration;
  1622.    *   unsigned int(32) id;
  1623.    *   string scheme_id_uri;
  1624.    *   string value;
  1625.    * }
  1626.    * unsigned int(8) message_data[];
  1627.    */
  1628.   parseEMSG_(reference, emsgSchemeIdUris, box) {
  1629.     let timescale;
  1630.     let id;
  1631.     let eventDuration;
  1632.     let schemeId;
  1633.     let startTime;
  1634.     let presentationTimeDelta;
  1635.     let value;
  1637.     if (box.version === 0) {
  1638.       schemeId = box.reader.readTerminatedString();
  1639.       value = box.reader.readTerminatedString();
  1640.       timescale = box.reader.readUint32();
  1641.       presentationTimeDelta = box.reader.readUint32();
  1642.       eventDuration = box.reader.readUint32();
  1643.       id = box.reader.readUint32();
  1644.       startTime = reference.startTime + (presentationTimeDelta / timescale);
  1645.     } else {
  1646.       timescale = box.reader.readUint32();
  1647.       const pts = box.reader.readUint64();
  1648.       startTime = (pts / timescale) + reference.timestampOffset;
  1649.       presentationTimeDelta = startTime - reference.startTime;
  1650.       eventDuration = box.reader.readUint32();
  1651.       id = box.reader.readUint32();
  1652.       schemeId = box.reader.readTerminatedString();
  1653.       value = box.reader.readTerminatedString();
  1654.     }
  1655.     const messageData = box.reader.readBytes(
  1656.         box.reader.getLength() - box.reader.getPosition());
  1659.     // See DASH sec. 5.10.3.3.1
  1660.     // If a DASH client detects an event message box with a scheme that is not
  1661.     // defined in MPD, the client is expected to ignore it.
  1662.     if ((emsgSchemeIdUris && emsgSchemeIdUris.includes(schemeId)) ||
  1663.         this.config_.dispatchAllEmsgBoxes) {
  1664.       // See DASH sec. 5.10.4.1
  1665.       // A special scheme in DASH used to signal manifest updates.
  1666.       if (schemeId == 'urn:mpeg:dash:event:2012') {
  1667.         this.playerInterface_.onManifestUpdate();
  1668.       } else {
  1669.         /** @type {shaka.extern.EmsgInfo} */
  1670.         const emsg = {
  1671.           startTime: startTime,
  1672.           endTime: startTime + (eventDuration / timescale),
  1673.           schemeIdUri: schemeId,
  1674.           value: value,
  1675.           timescale: timescale,
  1676.           presentationTimeDelta: presentationTimeDelta,
  1677.           eventDuration: eventDuration,
  1678.           id: id,
  1679.           messageData: messageData,
  1680.         };
  1682.         // Dispatch an event to notify the application about the emsg box.
  1683.         const eventName = shaka.Player.EventName.Emsg;
  1684.         const data = (new Map()).set('detail', emsg);
  1685.         const event = new shaka.util.FakeEvent(eventName, data);
  1686.         this.playerInterface_.onEvent(event);
  1687.       }
  1688.     }
  1689.   }
  1692.   /**
  1693.    * Evicts media to meet the max buffer behind limit.
  1694.    *
  1695.    * @param {shaka.media.StreamingEngine.MediaState_} mediaState
  1696.    * @param {number} presentationTime
  1697.    * @private
  1698.    */
  1699.   async evict_(mediaState, presentationTime) {
  1700.     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  1701.     shaka.log.v2(logPrefix, 'checking buffer length');
  1703.     // Use the max segment duration, if it is longer than the bufferBehind, to
  1704.     // avoid accidentally clearing too much data when dealing with a manifest
  1705.     // with a long keyframe interval.
  1706.     const bufferBehind = Math.max(this.config_.bufferBehind,
  1707.         this.manifest_.presentationTimeline.getMaxSegmentDuration());
  1709.     const startTime =
  1710.         this.playerInterface_.mediaSourceEngine.bufferStart(mediaState.type);
  1711.     if (startTime == null) {
  1712.       shaka.log.v2(logPrefix,
  1713.           'buffer behind okay because nothing buffered:',
  1714.           'presentationTime=' + presentationTime,
  1715.           'bufferBehind=' + bufferBehind);
  1716.       return;
  1717.     }
  1718.     const bufferedBehind = presentationTime - startTime;
  1720.     const overflow = bufferedBehind - bufferBehind;
  1721.     // See: https://github.com/shaka-project/shaka-player/issues/2982
  1722.     if (overflow <= 0.01) {
  1723.       shaka.log.v2(logPrefix,
  1724.           'buffer behind okay:',
  1725.           'presentationTime=' + presentationTime,
  1726.           'bufferedBehind=' + bufferedBehind,
  1727.           'bufferBehind=' + bufferBehind,
  1728.           'underflow=' + Math.abs(overflow));
  1729.       return;
  1730.     }
  1732.     shaka.log.v1(logPrefix,
  1733.         'buffer behind too large:',
  1734.         'presentationTime=' + presentationTime,
  1735.         'bufferedBehind=' + bufferedBehind,
  1736.         'bufferBehind=' + bufferBehind,
  1737.         'overflow=' + overflow);
  1739.     await this.playerInterface_.mediaSourceEngine.remove(mediaState.type,
  1740.         startTime, startTime + overflow);
  1742.     this.destroyer_.ensureNotDestroyed();
  1743.     shaka.log.v1(logPrefix, 'evicted ' + overflow + ' seconds');
  1744.   }
  1747.   /**
  1748.    * @param {shaka.media.StreamingEngine.MediaState_} mediaState
  1749.    * @return {boolean}
  1750.    * @private
  1751.    */
  1752.   static isEmbeddedText_(mediaState) {
  1753.     const MimeUtils = shaka.util.MimeUtils;
  1754.     const CEA608_MIME = MimeUtils.CEA608_CLOSED_CAPTION_MIMETYPE;
  1755.     const CEA708_MIME = MimeUtils.CEA708_CLOSED_CAPTION_MIMETYPE;
  1756.     return mediaState &&
  1757.         mediaState.type == shaka.util.ManifestParserUtils.ContentType.TEXT &&
  1758.         (mediaState.stream.mimeType == CEA608_MIME ||
  1759.          mediaState.stream.mimeType == CEA708_MIME);
  1760.   }
  1763.   /**
  1764.    * Fetches the given segment.
  1765.    *
  1766.    * @param {!shaka.media.StreamingEngine.MediaState_} mediaState
  1767.    * @param {(!shaka.media.InitSegmentReference|!shaka.media.SegmentReference)}
  1768.    *   reference
  1769.    * @param {?function(BufferSource):!Promise=} streamDataCallback
  1770.    *
  1771.    * @return {!Promise.<BufferSource>}
  1772.    * @private
  1773.    * @suppress {strictMissingProperties}
  1774.    */
  1775.   async fetch_(mediaState, reference, streamDataCallback) {
  1776.     const requestType = shaka.net.NetworkingEngine.RequestType.SEGMENT;
  1778.     const request = shaka.util.Networking.createSegmentRequest(
  1779.         reference.getUris(),
  1780.         reference.startByte,
  1781.         reference.endByte,
  1782.         this.config_.retryParameters,
  1783.         streamDataCallback);
  1785.     shaka.log.v2('fetching: reference=', reference);
  1787.     const stream = mediaState.stream;
  1788.     this.playerInterface_.modifySegmentRequest(
  1789.         request,
  1790.         {
  1791.           type: stream.type,
  1792.           init: reference instanceof shaka.media.InitSegmentReference,
  1793.           duration: reference.endTime - reference.startTime,
  1794.           mimeType: stream.mimeType,
  1795.           codecs: stream.codecs,
  1796.           bandwidth: stream.bandwidth,
  1797.         },
  1798.     );
  1800.     const op = this.playerInterface_.netEngine.request(requestType, request);
  1801.     mediaState.operation = op;
  1802.     const response = await op.promise;
  1803.     mediaState.operation = null;
  1804.     return response.data;
  1805.   }
  1808.   /**
  1809.    * Clears the buffer and schedules another update.
  1810.    * The optional parameter safeMargin allows to retain a certain amount
  1811.    * of buffer, which can help avoiding rebuffering events.
  1812.    * The value of the safe margin should be provided by the ABR manager.
  1813.    *
  1814.    * @param {!shaka.media.StreamingEngine.MediaState_} mediaState
  1815.    * @param {boolean} flush
  1816.    * @param {number} safeMargin
  1817.    * @private
  1818.    */
  1819.   async clearBuffer_(mediaState, flush, safeMargin) {
  1820.     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  1822.     goog.asserts.assert(
  1823.         !mediaState.performingUpdate && (mediaState.updateTimer == null),
  1824.         logPrefix + ' unexpected call to clearBuffer_()');
  1826.     mediaState.waitingToClearBuffer = false;
  1827.     mediaState.waitingToFlushBuffer = false;
  1828.     mediaState.clearBufferSafeMargin = 0;
  1829.     mediaState.clearingBuffer = true;
  1830.     mediaState.lastSegmentReference = null;
  1831.     mediaState.lastInitSegmentReference = null;
  1832.     mediaState.segmentIterator = null;
  1834.     shaka.log.debug(logPrefix, 'clearing buffer');
  1836.     if (safeMargin) {
  1837.       const presentationTime = this.playerInterface_.getPresentationTime();
  1838.       const duration = this.playerInterface_.mediaSourceEngine.getDuration();
  1839.       await this.playerInterface_.mediaSourceEngine.remove(
  1840.           mediaState.type, presentationTime + safeMargin, duration);
  1841.     } else {
  1842.       await this.playerInterface_.mediaSourceEngine.clear(mediaState.type);
  1843.       this.destroyer_.ensureNotDestroyed();
  1845.       if (flush) {
  1846.         await this.playerInterface_.mediaSourceEngine.flush(
  1847.             mediaState.type);
  1848.       }
  1849.     }
  1850.     this.destroyer_.ensureNotDestroyed();
  1852.     shaka.log.debug(logPrefix, 'cleared buffer');
  1853.     mediaState.clearingBuffer = false;
  1854.     mediaState.endOfStream = false;
  1855.     this.scheduleUpdate_(mediaState, 0);
  1856.   }
  1859.   /**
  1860.    * Schedules |mediaState|'s next update.
  1861.    *
  1862.    * @param {!shaka.media.StreamingEngine.MediaState_} mediaState
  1863.    * @param {number} delay The delay in seconds.
  1864.    * @private
  1865.    */
  1866.   scheduleUpdate_(mediaState, delay) {
  1867.     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
  1869.     // If the text's update is canceled and its mediaState is deleted, stop
  1870.     // scheduling another update.
  1871.     const type = mediaState.type;
  1872.     if (type == shaka.util.ManifestParserUtils.ContentType.TEXT &&
  1873.           !this.mediaStates_.has(type)) {
  1874.       shaka.log.v1(logPrefix, 'Text stream is unloaded. No update is needed.');
  1875.       return;
  1876.     }
  1878.     shaka.log.v2(logPrefix, 'updating in ' + delay + ' seconds');
  1879.     goog.asserts.assert(mediaState.updateTimer == null,
  1880.         logPrefix + ' did not expect update to be scheduled');
  1882.     mediaState.updateTimer = new shaka.util.DelayedTick(async () => {
  1883.       try {
  1884.         await this.onUpdate_(mediaState);
  1885.       } catch (error) {
  1886.         if (this.playerInterface_) {
  1887.           this.playerInterface_.onError(error);
  1888.         }
  1889.       }
  1890.     }).tickAfter(delay);
  1891.   }
  1894.   /**
  1895.    * If |mediaState| is scheduled to update, stop it.
  1896.    *
  1897.    * @param {shaka.media.StreamingEngine.MediaState_} mediaState
  1898.    * @private
  1899.    */
  1900.   cancelUpdate_(mediaState) {
  1901.     if (mediaState.updateTimer == null) {
  1902.       return;
  1903.     }
  1905.     mediaState.updateTimer.stop();
  1906.     mediaState.updateTimer = null;
  1907.   }
  1910.   /**
  1911.    * If |mediaState| holds any in-progress operations, abort them.
  1912.    *
  1913.    * @return {!Promise}
  1914.    * @private
  1915.    */
  1916.   async abortOperations_(mediaState) {
  1917.     if (mediaState.operation) {
  1918.       await mediaState.operation.abort();
  1919.     }
  1920.   }
  1922.   /**
  1923.    * Handle streaming errors by delaying, then notifying the application by
  1924.    * error callback and by streaming failure callback.
  1925.    *
  1926.    * @param {!shaka.util.Error} error
  1927.    * @return {!Promise}
  1928.    * @private
  1929.    */
  1930.   async handleStreamingError_(error) {
  1931.     // If we invoke the callback right away, the application could trigger a
  1932.     // rapid retry cycle that could be very unkind to the server.  Instead,
  1933.     // use the backoff system to delay and backoff the error handling.
  1934.     await this.failureCallbackBackoff_.attempt();
  1935.     this.destroyer_.ensureNotDestroyed();
  1937.     // First fire an error event.
  1938.     this.playerInterface_.onError(error);
  1940.     // If the error was not handled by the application, call the failure
  1941.     // callback.
  1942.     if (!error.handled) {
  1943.       this.config_.failureCallback(error);
  1944.     }
  1945.   }
  1947.   /**
  1948.    * @param {shaka.media.StreamingEngine.MediaState_} mediaState
  1949.    * @return {string} A log prefix of the form ($CONTENT_TYPE:$STREAM_ID), e.g.,
  1950.    *   "(audio:5)" or "(video:hd)".
  1951.    * @private
  1952.    */
  1953.   static logPrefix_(mediaState) {
  1954.     return '(' + mediaState.type + ':' + mediaState.stream.id + ')';
  1955.   }
  1956. };
  1959. /**
  1960.  * @typedef {{
  1961.  *   getPresentationTime: function():number,
  1962.  *   getBandwidthEstimate: function():number,
  1963.  *   modifySegmentRequest: function(shaka.extern.Request,
  1964.  *     shaka.util.CmcdManager.SegmentInfo),
  1965.  *   mediaSourceEngine: !shaka.media.MediaSourceEngine,
  1966.  *   netEngine: shaka.net.NetworkingEngine,
  1967.  *   onError: function(!shaka.util.Error),
  1968.  *   onEvent: function(!Event),
  1969.  *   onManifestUpdate: function(),
  1970.  *   onSegmentAppended: function(),
  1971.  *   onInitSegmentAppended: function(!number,!shaka.media.InitSegmentReference)
  1972.  * }}
  1973.  *
  1974.  * @property {function():number} getPresentationTime
  1975.  *   Get the position in the presentation (in seconds) of the content that the
  1976.  *   viewer is seeing on screen right now.
  1977.  * @property {function():number} getBandwidthEstimate
  1978.  *   Get the estimated bandwidth in bits per second.
  1979.  * @property {function(shaka.extern.Request,
  1980.  *   shaka.extern.Cmcd.SegmentInfo)} modifySegmentRequest
  1981.  *   The request modifier
  1982.  * @property {!shaka.media.MediaSourceEngine} mediaSourceEngine
  1983.  *   The MediaSourceEngine. The caller retains ownership.
  1984.  * @property {shaka.net.NetworkingEngine} netEngine
  1985.  *   The NetworkingEngine instance to use. The caller retains ownership.
  1986.  * @property {function(!shaka.util.Error)} onError
  1987.  *   Called when an error occurs. If the error is recoverable (see
  1988.  *   {@link shaka.util.Error}) then the caller may invoke either
  1989.  *   StreamingEngine.switch*() or StreamingEngine.seeked() to attempt recovery.
  1990.  * @property {function(!Event)} onEvent
  1991.  *   Called when an event occurs that should be sent to the app.
  1992.  * @property {function()} onManifestUpdate
  1993.  *   Called when an embedded 'emsg' box should trigger a manifest update.
  1994.  * @property {function()} onSegmentAppended
  1995.  *   Called after a segment is successfully appended to a MediaSource.
  1996.  * @property
  1997.  *  {function(!number, !shaka.media.InitSegmentReference)} onInitSegmentAppended
  1998.  *   Called when an init segment is appended to a MediaSource.
  1999.  */
  2000. shaka.media.StreamingEngine.PlayerInterface;
  2003. /**
  2004.  * @typedef {{
  2005.  *   type: shaka.util.ManifestParserUtils.ContentType,
  2006.  *   stream: shaka.extern.Stream,
  2007.  *   segmentIterator: shaka.media.SegmentIterator,
  2008.  *   lastSegmentReference: shaka.media.SegmentReference,
  2009.  *   lastInitSegmentReference: shaka.media.InitSegmentReference,
  2010.  *   lastTimestampOffset: ?number,
  2011.  *   lastAppendWindowStart: ?number,
  2012.  *   lastAppendWindowEnd: ?number,
  2013.  *   restoreStreamAfterTrickPlay: ?shaka.extern.Stream,
  2014.  *   endOfStream: boolean,
  2015.  *   performingUpdate: boolean,
  2016.  *   updateTimer: shaka.util.DelayedTick,
  2017.  *   waitingToClearBuffer: boolean,
  2018.  *   waitingToFlushBuffer: boolean,
  2019.  *   clearBufferSafeMargin: number,
  2020.  *   clearingBuffer: boolean,
  2021.  *   recovering: boolean,
  2022.  *   hasError: boolean,
  2023.  *   operation: shaka.net.NetworkingEngine.PendingRequest
  2024.  * }}
  2025.  *
  2026.  * @description
  2027.  * Contains the state of a logical stream, i.e., a sequence of segmented data
  2028.  * for a particular content type. At any given time there is a Stream object
  2029.  * associated with the state of the logical stream.
  2030.  *
  2031.  * @property {shaka.util.ManifestParserUtils.ContentType} type
  2032.  *   The stream's content type, e.g., 'audio', 'video', or 'text'.
  2033.  * @property {shaka.extern.Stream} stream
  2034.  *   The current Stream.
  2035.  * @property {shaka.media.SegmentIndexIterator} segmentIterator
  2036.  *   An iterator through the segments of |stream|.
  2037.  * @property {shaka.media.SegmentReference} lastSegmentReference
  2038.  *   The SegmentReference of the last segment that was appended.
  2039.  * @property {shaka.media.InitSegmentReference} lastInitSegmentReference
  2040.  *   The InitSegmentReference of the last init segment that was appended.
  2041.  * @property {?number} lastTimestampOffset
  2042.  *   The last timestamp offset given to MediaSourceEngine for this type.
  2043.  * @property {?number} lastAppendWindowStart
  2044.  *   The last append window start given to MediaSourceEngine for this type.
  2045.  * @property {?number} lastAppendWindowEnd
  2046.  *   The last append window end given to MediaSourceEngine for this type.
  2047.  * @property {?shaka.extern.Stream} restoreStreamAfterTrickPlay
  2048.  *   The Stream to restore after trick play mode is turned off.
  2049.  * @property {boolean} endOfStream
  2050.  *   True indicates that the end of the buffer has hit the end of the
  2051.  *   presentation.
  2052.  * @property {boolean} performingUpdate
  2053.  *   True indicates that an update is in progress.
  2054.  * @property {shaka.util.DelayedTick} updateTimer
  2055.  *   A timer used to update the media state.
  2056.  * @property {boolean} waitingToClearBuffer
  2057.  *   True indicates that the buffer must be cleared after the current update
  2058.  *   finishes.
  2059.  * @property {boolean} waitingToFlushBuffer
  2060.  *   True indicates that the buffer must be flushed after it is cleared.
  2061.  * @property {number} clearBufferSafeMargin
  2062.  *   The amount of buffer to retain when clearing the buffer after the update.
  2063.  * @property {boolean} clearingBuffer
  2064.  *   True indicates that the buffer is being cleared.
  2065.  * @property {boolean} recovering
  2066.  *   True indicates that the last segment was not appended because it could not
  2067.  *   fit in the buffer.
  2068.  * @property {boolean} hasError
  2069.  *   True indicates that the stream has encountered an error and has stopped
  2070.  *   updating.
  2071.  * @property {shaka.net.NetworkingEngine.PendingRequest} operation
  2072.  *   Operation with the number of bytes to be downloaded.
  2073.  */
  2074. shaka.media.StreamingEngine.MediaState_;
  2077. /**
  2078.  * The fudge factor for appendWindowStart.  By adjusting the window backward, we
  2079.  * avoid rounding errors that could cause us to remove the keyframe at the start
  2080.  * of the Period.
  2081.  *
  2082.  * NOTE: This was increased as part of the solution to
  2083.  * https://github.com/shaka-project/shaka-player/issues/1281
  2084.  *
  2085.  * @const {number}
  2086.  * @private
  2087.  */
  2088. shaka.media.StreamingEngine.APPEND_WINDOW_START_FUDGE_ = 0.1;
  2091. /**
  2092.  * The fudge factor for appendWindowEnd.  By adjusting the window backward, we
  2093.  * avoid rounding errors that could cause us to remove the last few samples of
  2094.  * the Period.  This rounding error could then create an artificial gap and a
  2095.  * stutter when the gap-jumping logic takes over.
  2096.  *
  2097.  * https://github.com/shaka-project/shaka-player/issues/1597
  2098.  *
  2099.  * @const {number}
  2100.  * @private
  2101.  */
  2102. shaka.media.StreamingEngine.APPEND_WINDOW_END_FUDGE_ = 0.01;
  2105. /**
  2106.  * The maximum number of segments by which a stream can get ahead of other
  2107.  * streams.
  2108.  *
  2109.  * Introduced to keep StreamingEngine from letting one media type get too far
  2110.  * ahead of another.  For example, audio segments are typically much smaller
  2111.  * than video segments, so in the time it takes to fetch one video segment, we
  2112.  * could fetch many audio segments.  This doesn't help with buffering, though,
  2113.  * since the intersection of the two buffered ranges is what counts.
  2114.  *
  2115.  * @const {number}
  2116.  * @private
  2117.  */
  2118. shaka.media.StreamingEngine.MAX_RUN_AHEAD_SEGMENTS_ = 1;