Source: lib/media/playhead.js

  1. /*! @license
  2.  * Shaka Player
  3.  * Copyright 2016 Google LLC
  4.  * SPDX-License-Identifier: Apache-2.0
  5.  */
  7. goog.provide('shaka.media.MediaSourcePlayhead');
  8. goog.provide('shaka.media.Playhead');
  9. goog.provide('shaka.media.SrcEqualsPlayhead');
  11. goog.require('goog.asserts');
  12. goog.require('shaka.log');
  13. goog.require('shaka.media.GapJumpingController');
  14. goog.require('shaka.media.StallDetector');
  15. goog.require('shaka.media.StallDetector.MediaElementImplementation');
  16. goog.require('shaka.media.TimeRangesUtils');
  17. goog.require('shaka.media.VideoWrapper');
  18. goog.require('shaka.util.EventManager');
  19. goog.require('shaka.util.IReleasable');
  20. goog.require('shaka.util.MediaReadyState');
  21. goog.require('shaka.util.Timer');
  22. goog.requireType('shaka.media.PresentationTimeline');
  25. /**
  26.  * Creates a Playhead, which manages the video's current time.
  27.  *
  28.  * The Playhead provides mechanisms for setting the presentation's start time,
  29.  * restricting seeking to valid time ranges, and stopping playback for startup
  30.  * and re-buffering.
  31.  *
  32.  * @extends {shaka.util.IReleasable}
  33.  * @interface
  34.  */
  35. shaka.media.Playhead = class {
  36.   /**
  37.    * Called when the Player is ready to begin playback. Anything that depends
  38.    * on setStartTime() should be done here, not in the constructor.
  39.    *
  40.    * @see https://github.com/shaka-project/shaka-player/issues/4244
  41.    */
  42.   ready() {}
  44.   /**
  45.    * Set the start time. If the content has already started playback, this will
  46.    * be ignored.
  47.    *
  48.    * @param {number} startTime
  49.    */
  50.   setStartTime(startTime) {}
  52.   /**
  53.    * Get the number of playback stalls detected by the StallDetector.
  54.    *
  55.    * @return {number}
  56.    */
  57.   getStallsDetected() {}
  59.   /**
  60.    * Get the number of playback gaps jumped by the GapJumpingController.
  61.    *
  62.    * @return {number}
  63.    */
  64.   getGapsJumped() {}
  66.   /**
  67.    * Get the current playhead position. The position will be restricted to valid
  68.    * time ranges.
  69.    *
  70.    * @return {number}
  71.    */
  72.   getTime() {}
  74.   /**
  75.    * Notify the playhead that the buffered ranges have changed.
  76.    */
  77.   notifyOfBufferingChange() {}
  78. };
  81. /**
  82.  * A playhead implementation that only relies on the media element.
  83.  *
  84.  * @implements {shaka.media.Playhead}
  85.  * @final
  86.  */
  87. shaka.media.SrcEqualsPlayhead = class {
  88.   /**
  89.    * @param {!HTMLMediaElement} mediaElement
  90.    */
  91.   constructor(mediaElement) {
  92.     /** @private {HTMLMediaElement} */
  93.     this.mediaElement_ = mediaElement;
  94.     /** @private {boolean} */
  95.     this.started_ = false;
  96.     /** @private {?number} */
  97.     this.startTime_ = null;
  99.     /** @private {shaka.util.EventManager} */
  100.     this.eventManager_ = new shaka.util.EventManager();
  101.   }
  103.   /** @override */
  104.   ready() {
  105.     goog.asserts.assert(
  106.         this.mediaElement_ != null,
  107.         'Playhead should not be released before calling ready()',
  108.     );
  110.     // We listen for the loaded-data-event so that we know when we can
  111.     // interact with |currentTime|.
  112.     const onLoaded = () => {
  113.       if (this.startTime_ == null ||
  114.           (this.startTime_ == 0 && this.mediaElement_.duration != Infinity)) {
  115.         this.started_ = true;
  116.       } else {
  117.         const currentTime = this.mediaElement_.currentTime;
  118.         let newTime = this.startTime_;
  119.         // Using the currentTime allows using a negative number in Live HLS
  120.         if (this.startTime_ < 0) {
  121.           newTime = Math.max(0, currentTime + this.startTime_);
  122.         }
  123.         if (currentTime != newTime) {
  124.           // Startup is complete only when the video element acknowledges the
  125.           // seek.
  126.           this.eventManager_.listenOnce(this.mediaElement_, 'seeking', () => {
  127.             this.started_ = true;
  128.           });
  129.           this.mediaElement_.currentTime = newTime;
  130.         } else {
  131.           this.started_ = true;
  132.         }
  133.       }
  134.     };
  136.     shaka.util.MediaReadyState.waitForReadyState(this.mediaElement_,
  137.         HTMLMediaElement.HAVE_CURRENT_DATA,
  138.         this.eventManager_, () => {
  139.           onLoaded();
  140.         });
  141.   }
  143.   /** @override */
  144.   release() {
  145.     if (this.eventManager_) {
  146.       this.eventManager_.release();
  147.       this.eventManager_ = null;
  148.     }
  150.     this.mediaElement_ = null;
  151.   }
  153.   /** @override */
  154.   setStartTime(startTime) {
  155.     // If we have already started playback, ignore updates to the start time.
  156.     // This is just to make things consistent.
  157.     this.startTime_ = this.started_ ? this.startTime_ : startTime;
  158.   }
  160.   /** @override */
  161.   getTime() {
  162.     // If we have not started playback yet, return the start time. However once
  163.     // we start playback we assume that we can always return the current time.
  164.     const time = this.started_ ?
  165.                  this.mediaElement_.currentTime :
  166.                  this.startTime_;
  168.     // In the case that we have not started playback, but the start time was
  169.     // never set, we don't know what the start time should be. To ensure we
  170.     // always return a number, we will default back to 0.
  171.     return time || 0;
  172.   }
  174.   /** @override */
  175.   getStallsDetected() {
  176.     return 0;
  177.   }
  179.   /** @override */
  180.   getGapsJumped() {
  181.     return 0;
  182.   }
  184.   /** @override */
  185.   notifyOfBufferingChange() {}
  186. };
  189. /**
  190.  * A playhead implementation that relies on the media element and a manifest.
  191.  * When provided with a manifest, we can provide more accurate control than
  192.  * the SrcEqualsPlayhead.
  193.  *
  194.  * TODO: Clean up and simplify Playhead.  There are too many layers of, methods
  195.  *       for, and conditions on timestamp adjustment.
  196.  *
  197.  * @implements {shaka.media.Playhead}
  198.  * @final
  199.  */
  200. shaka.media.MediaSourcePlayhead = class {
  201.   /**
  202.    * @param {!HTMLMediaElement} mediaElement
  203.    * @param {shaka.extern.Manifest} manifest
  204.    * @param {shaka.extern.StreamingConfiguration} config
  205.    * @param {?number} startTime
  206.    *     The playhead's initial position in seconds. If null, defaults to the
  207.    *     start of the presentation for VOD and the live-edge for live.
  208.    * @param {function()} onSeek
  209.    *     Called when the user agent seeks to a time within the presentation
  210.    *     timeline.
  211.    * @param {function(!Event)} onEvent
  212.    *     Called when an event is raised to be sent to the application.
  213.    */
  214.   constructor(mediaElement, manifest, config, startTime, onSeek, onEvent) {
  215.     /**
  216.      * The seek range must be at least this number of seconds long. If it is
  217.      * smaller than this, change it to be this big so we don't repeatedly seek
  218.      * to keep within a zero-width window.
  219.      *
  220.      * This is 3s long, to account for the weaker hardware on platforms like
  221.      * Chromecast.
  222.      *
  223.      * @private {number}
  224.      */
  225.     this.minSeekRange_ = 3.0;
  227.     /** @private {HTMLMediaElement} */
  228.     this.mediaElement_ = mediaElement;
  230.     /** @private {shaka.media.PresentationTimeline} */
  231.     this.timeline_ = manifest.presentationTimeline;
  233.     /** @private {number} */
  234.     this.minBufferTime_ = manifest.minBufferTime || 0;
  236.     /** @private {?shaka.extern.StreamingConfiguration} */
  237.     this.config_ = config;
  239.     /** @private {function()} */
  240.     this.onSeek_ = onSeek;
  242.     /** @private {?number} */
  243.     this.lastCorrectiveSeek_ = null;
  245.     /** @private {shaka.media.StallDetector} */
  246.     this.stallDetector_ =
  247.         this.createStallDetector_(mediaElement, config, onEvent);
  249.     /** @private {shaka.media.GapJumpingController} */
  250.     this.gapController_ = new shaka.media.GapJumpingController(
  251.         mediaElement,
  252.         manifest.presentationTimeline,
  253.         config,
  254.         this.stallDetector_,
  255.         onEvent);
  257.     /** @private {shaka.media.VideoWrapper} */
  258.     this.videoWrapper_ = new shaka.media.VideoWrapper(
  259.         mediaElement,
  260.         () => this.onSeeking_(),
  261.         (realStartTime) => this.onStarted_(realStartTime),
  262.         () => this.getStartTime_(startTime));
  264.     /** @type {shaka.util.Timer} */
  265.     this.checkWindowTimer_ = new shaka.util.Timer(() => {
  266.       this.onPollWindow_();
  267.     });
  268.   }
  270.   /** @override */
  271.   ready() {
  272.     this.checkWindowTimer_.tickEvery(/* seconds= */ 0.25);
  273.   }
  275.   /** @override */
  276.   release() {
  277.     if (this.videoWrapper_) {
  278.       this.videoWrapper_.release();
  279.       this.videoWrapper_ = null;
  280.     }
  282.     if (this.gapController_) {
  283.       this.gapController_.release();
  284.       this.gapController_= null;
  285.     }
  287.     if (this.checkWindowTimer_) {
  288.       this.checkWindowTimer_.stop();
  289.       this.checkWindowTimer_ = null;
  290.     }
  292.     this.config_ = null;
  293.     this.timeline_ = null;
  294.     this.videoWrapper_ = null;
  295.     this.mediaElement_ = null;
  297.     this.onSeek_ = () => {};
  298.   }
  300.   /** @override */
  301.   setStartTime(startTime) {
  302.     this.videoWrapper_.setTime(startTime);
  303.   }
  305.   /** @override */
  306.   getTime() {
  307.     const time = this.videoWrapper_.getTime();
  309.     // Although we restrict the video's currentTime elsewhere, clamp it here to
  310.     // ensure timing issues don't cause us to return a time outside the segment
  311.     // availability window.  E.g., the user agent seeks and calls this function
  312.     // before we receive the 'seeking' event.
  313.     //
  314.     // We don't buffer when the livestream video is paused and the playhead time
  315.     // is out of the seek range; thus, we do not clamp the current time when the
  316.     // video is paused.
  317.     // https://github.com/shaka-project/shaka-player/issues/1121
  318.     if (this.mediaElement_.readyState > 0 && !this.mediaElement_.paused) {
  319.       return this.clampTime_(time);
  320.     }
  322.     return time;
  323.   }
  325.   /** @override */
  326.   getStallsDetected() {
  327.     return this.stallDetector_ ? this.stallDetector_.getStallsDetected() : 0;
  328.   }
  330.   /** @override */
  331.   getGapsJumped() {
  332.     return this.gapController_.getGapsJumped();
  333.   }
  335.   /**
  336.    * Gets the playhead's initial position in seconds.
  337.    *
  338.    * @param {?number} startTime
  339.    * @return {number}
  340.    * @private
  341.    */
  342.   getStartTime_(startTime) {
  343.     if (startTime == null) {
  344.       if (this.timeline_.getDuration() < Infinity) {
  345.         // If the presentation is VOD, or if the presentation is live but has
  346.         // finished broadcasting, then start from the beginning.
  347.         startTime = this.timeline_.getSeekRangeStart();
  348.       } else {
  349.         // Otherwise, start near the live-edge.
  350.         startTime = this.timeline_.getSeekRangeEnd();
  351.       }
  352.     } else if (startTime < 0) {
  353.       // For live streams, if the startTime is negative, start from a certain
  354.       // offset time from the live edge.  If the offset from the live edge is
  355.       // not available, start from the current available segment start point
  356.       // instead, handled by clampTime_().
  357.       startTime = this.timeline_.getSeekRangeEnd() + startTime;
  358.     }
  360.     return this.clampSeekToDuration_(this.clampTime_(startTime));
  361.   }
  363.   /** @override */
  364.   notifyOfBufferingChange() {
  365.     this.gapController_.onSegmentAppended();
  366.   }
  368.   /**
  369.    * Called on a recurring timer to keep the playhead from falling outside the
  370.    * availability window.
  371.    *
  372.    * @private
  373.    */
  374.   onPollWindow_() {
  375.     // Don't catch up to the seek range when we are paused or empty.
  376.     // The definition of "seeking" says that we are seeking until the buffered
  377.     // data intersects with the playhead.  If we fall outside of the seek range,
  378.     // it doesn't matter if we are in a "seeking" state.  We can and should go
  379.     // ahead and catch up while seeking.
  380.     if (this.mediaElement_.readyState == 0 || this.mediaElement_.paused) {
  381.       return;
  382.     }
  384.     const currentTime = this.videoWrapper_.getTime();
  385.     let seekStart = this.timeline_.getSeekRangeStart();
  386.     const seekEnd = this.timeline_.getSeekRangeEnd();
  388.     if (seekEnd - seekStart < this.minSeekRange_) {
  389.       seekStart = seekEnd - this.minSeekRange_;
  390.     }
  392.     if (currentTime < seekStart) {
  393.       // The seek range has moved past the playhead.  Move ahead to catch up.
  394.       const targetTime = this.reposition_(currentTime);
  395.       shaka.log.info('Jumping forward ' + (targetTime - currentTime) +
  396.                      ' seconds to catch up with the seek range.');
  397.       this.mediaElement_.currentTime = targetTime;
  398.     }
  399.   }
  401.   /**
  402.    * Called when the video element has started up and is listening for new seeks
  403.    *
  404.    * @param {number} startTime
  405.    * @private
  406.    */
  407.   onStarted_(startTime) {
  408.     this.gapController_.onStarted(startTime);
  409.   }
  411.   /**
  412.    * Handles when a seek happens on the video.
  413.    *
  414.    * @private
  415.    */
  416.   onSeeking_() {
  417.     this.gapController_.onSeeking();
  418.     const currentTime = this.videoWrapper_.getTime();
  419.     const targetTime = this.reposition_(currentTime);
  421.     const gapLimit = shaka.media.GapJumpingController.BROWSER_GAP_TOLERANCE;
  422.     if (Math.abs(targetTime - currentTime) > gapLimit) {
  423.       // You can only seek like this every so often. This is to prevent an
  424.       // infinite loop on systems where changing currentTime takes a significant
  425.       // amount of time (e.g. Chromecast).
  426.       const time = Date.now() / 1000;
  427.       if (!this.lastCorrectiveSeek_ || this.lastCorrectiveSeek_ < time - 1) {
  428.         this.lastCorrectiveSeek_ = time;
  429.         this.videoWrapper_.setTime(targetTime);
  430.         return;
  431.       }
  432.     }
  434.     shaka.log.v1('Seek to ' + currentTime);
  435.     this.onSeek_();
  436.   }
  438.   /**
  439.    * Clamp seek times and playback start times so that we never seek to the
  440.    * presentation duration.  Seeking to or starting at duration does not work
  441.    * consistently across browsers.
  442.    *
  443.    * @see https://github.com/shaka-project/shaka-player/issues/979
  444.    * @param {number} time
  445.    * @return {number} The adjusted seek time.
  446.    * @private
  447.    */
  448.   clampSeekToDuration_(time) {
  449.     const duration = this.timeline_.getDuration();
  450.     if (time >= duration) {
  451.       goog.asserts.assert(this.config_.durationBackoff >= 0,
  452.           'Duration backoff must be non-negative!');
  453.       return duration - this.config_.durationBackoff;
  454.     }
  455.     return time;
  456.   }
  458.   /**
  459.    * Computes a new playhead position that's within the presentation timeline.
  460.    *
  461.    * @param {number} currentTime
  462.    * @return {number} The time to reposition the playhead to.
  463.    * @private
  464.    */
  465.   reposition_(currentTime) {
  466.     goog.asserts.assert(
  467.         this.config_,
  468.         'Cannot reposition playhead when it has beeen destroyed');
  470.     /** @type {function(number)} */
  471.     const isBuffered = (playheadTime) => shaka.media.TimeRangesUtils.isBuffered(
  472.         this.mediaElement_.buffered, playheadTime);
  474.     const rebufferingGoal = Math.max(
  475.         this.minBufferTime_,
  476.         this.config_.rebufferingGoal);
  478.     const safeSeekOffset = this.config_.safeSeekOffset;
  480.     let start = this.timeline_.getSeekRangeStart();
  481.     const end = this.timeline_.getSeekRangeEnd();
  482.     const duration = this.timeline_.getDuration();
  484.     if (end - start < this.minSeekRange_) {
  485.       start = end - this.minSeekRange_;
  486.     }
  488.     // With live content, the beginning of the availability window is moving
  489.     // forward.  This means we cannot seek to it since we will "fall" outside
  490.     // the window while we buffer.  So we define a "safe" region that is far
  491.     // enough away.  For VOD, |safe == start|.
  492.     const safe = this.timeline_.getSafeSeekRangeStart(rebufferingGoal);
  494.     // These are the times to seek to rather than the exact destinations.  When
  495.     // we seek, we will get another event (after a slight delay) and these steps
  496.     // will run again.  So if we seeked directly to |start|, |start| would move
  497.     // on the next call and we would loop forever.
  498.     const seekStart = this.timeline_.getSafeSeekRangeStart(safeSeekOffset);
  499.     const seekSafe = this.timeline_.getSafeSeekRangeStart(
  500.         rebufferingGoal + safeSeekOffset);
  502.     if (currentTime >= duration) {
  503.       shaka.log.v1('Playhead past duration.');
  504.       return this.clampSeekToDuration_(currentTime);
  505.     }
  507.     if (currentTime > end) {
  508.       shaka.log.v1('Playhead past end.');
  509.       return end;
  510.     }
  512.     if (currentTime < start) {
  513.       if (isBuffered(seekStart)) {
  514.         shaka.log.v1('Playhead before start & start is buffered');
  515.         return seekStart;
  516.       } else {
  517.         shaka.log.v1('Playhead before start & start is unbuffered');
  518.         return seekSafe;
  519.       }
  520.     }
  522.     if (currentTime >= safe || isBuffered(currentTime)) {
  523.       shaka.log.v1('Playhead in safe region or in buffered region.');
  524.       return currentTime;
  525.     } else {
  526.       shaka.log.v1('Playhead outside safe region & in unbuffered region.');
  527.       return seekSafe;
  528.     }
  529.   }
  531.   /**
  532.    * Clamps the given time to the seek range.
  533.    *
  534.    * @param {number} time The time in seconds.
  535.    * @return {number} The clamped time in seconds.
  536.    * @private
  537.    */
  538.   clampTime_(time) {
  539.     const start = this.timeline_.getSeekRangeStart();
  540.     if (time < start) {
  541.       return start;
  542.     }
  544.     const end = this.timeline_.getSeekRangeEnd();
  545.     if (time > end) {
  546.       return end;
  547.     }
  549.     return time;
  550.   }
  552.   /**
  553.    * Create and configure a stall detector using the player's streaming
  554.    * configuration settings. If the player is configured to have no stall
  555.    * detector, this will return |null|.
  556.    *
  557.    * @param {!HTMLMediaElement} mediaElement
  558.    * @param {shaka.extern.StreamingConfiguration} config
  559.    * @param {function(!Event)} onEvent
  560.    *     Called when an event is raised to be sent to the application.
  561.    * @return {shaka.media.StallDetector}
  562.    * @private
  563.    */
  564.   createStallDetector_(mediaElement, config, onEvent) {
  565.     if (!config.stallEnabled) {
  566.       return null;
  567.     }
  569.     // Cache the values from the config so that changes to the config won't
  570.     // change the initialized behaviour.
  571.     const threshold = config.stallThreshold;
  572.     const skip = config.stallSkip;
  574.     // When we see a stall, we will try to "jump-start" playback by moving the
  575.     // playhead forward.
  576.     const detector = new shaka.media.StallDetector(
  577.         new shaka.media.StallDetector.MediaElementImplementation(mediaElement),
  578.         threshold, onEvent);
  580.     detector.onStall((at, duration) => {
  581.       shaka.log.debug(`Stall detected at ${at} for ${duration} seconds.`);
  583.       if (skip) {
  584.         shaka.log.debug(`Seeking forward ${skip} seconds to break stall.`);
  585.         mediaElement.currentTime += skip;
  586.       } else {
  587.         shaka.log.debug('Pausing and unpausing to break stall.');
  588.         mediaElement.pause();
  589.         mediaElement.play();
  590.       }
  591.     });
  593.     return detector;
  594.   }
  595. };