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设置 Player 类

在 video_player.js 中，定义一个视频播放器封装容器类，以启动和控制 dash.js 播放器。

设置宽带播放器

通过创建视频和封装容器标记，定义要在应用中的什么位置放置宽带播放器：

<div id="broadband-wrapper">
    <video id="broadband-video"></video>
</div>index.html

创建视频播放器

使用 HTML 元素、dash.js 播放器的变量以及其他类方法可用的回调初始化视频播放器类。

/**
 * Video player wrapper class to control ad creative playback with dash.js in
 * broadband.
 */
var VideoPlayer = function() {
  this.videoElement = document.querySelector('video');
  this.broadbandWrapper = document.getElementById('broadband-wrapper');
  this.player = dashjs.MediaPlayer().create();
  this.onAdPodEndedCallback = null;

  // Function passed in VideoPlayer.prototype.setEmsgEventHandler.
  this.onCustomEventHandler = null;
  //  Scope (this) passed in VideoPlayer.prototype.setEmsgEventHandler.
  this.customEventHandlerScope = null;

  // Function to remove all of player event listeners.
  this.cleanUpPlayerListener = null;
  debugView.log('Player: Creating dash.js player');
};video_player.js

定义播放控制函数

如需显示广告播放器并附加视频视图，请创建 VideoPlayer.play() 方法。之后，创建 create VideoPlayer.stop() 方法，以处理广告连播结束后的清理工作。

/** Starts playback of ad stream. */
VideoPlayer.prototype.play = function() {
  debugView.log('Player: Start playback');
  this.show();
  this.player.attachView(this.videoElement);
};

/** Stops ad stream playback and deconstructs player. */
VideoPlayer.prototype.stop = function() {
  debugView.log('Player: Request to stop player');
  if (this.cleanUpPlayerListener) {
    this.cleanUpPlayerListener();
  }
  this.player.reset();
  this.player.attachView(null);
  this.player.attachSource(null);
  this.player = null;
  this.hide();
};video_player.js

预加载广告串流清单

如需确保在内容流式传输期间和广告插播开始前充分加载广告，请使用 VideoPlayer.preload() 和 VideoPlayer.isPreloaded()。

1. 预加载广告串流

创建 VideoPlayer.preload() 方法以预加载广告串流清单，并在广告插播时间之前建立广告缓冲区。您必须将玩家在线播放设置 'cacheInitSegments' 更新为 true。通过更新设置，您可以启用缓存 init 分段，从而避免在切换到广告时出现延迟。

/**
 * Starts ad stream prefetching into Media Source Extensions (MSE) buffer.
 * @param {string} url manifest url for ad stream playback.
 */
VideoPlayer.prototype.preload = function(url) {
  if (!this.player) {
    this.player = dashjs.MediaPlayer().create();
  }
  debugView.log('Player: init with ' + url);
  this.player.initialize(/* HTMLVideoElement */ null, url, /* autoplay */ true);

  this.player.updateSettings({
    'debug': {
      'logLevel': dashjs.Debug.LOG_LEVEL_WARNING,
      'dispatchEvent': true,  // flip to false to hide all debug events.
    },
    'streaming': {
      'cacheInitSegments': true,
    }
  });
  this.player.preload();
  this.attachPlayerListener();
  debugView.log('Player: Pre-loading into MSE buffer');
};video_player.js

2. 检查预加载的广告缓冲区

创建 VideoPlayer.isPreloaded() 方法，用于检查与应用中设置的缓冲区阈值相比，是否预加载了足够的广告缓冲区：

// Ads will only play with 10 or more seconds of ad loaded.
var MIN_BUFFER_THRESHOLD = 10;video_player.js

/**
 * Checks if the ad is preloaded and ready to play.
 * @return {boolean} whether the ad buffer level is sufficient.
 */
VideoPlayer.prototype.isPreloaded = function() {
  var currentBufferLevel = this.player.getDashMetrics()
      .getCurrentBufferLevel('video', true);
  return currentBufferLevel >= MIN_BUFFER_THRESHOLD;
};video_player.js

附加播放器监听器

如需为 dash.js 播放器事件添加事件监听器，请创建 VideoPlayer.attachPlayerListener() 方法：PLAYBACK_PLAYING、PLAYBACK_ENDED、LOG 和 ERROR。除了设置清理函数以移除这些监听器之外，此方法还会处理 scheme ID URI 的事件。

var SCHEME_ID_URI = 'https://developer.apple.com/streaming/emsg-id3';video_player.js

/** Attaches event listener for various dash.js events.*/
VideoPlayer.prototype.attachPlayerListener = function() {
  var playingHandler = function() {
    this.onAdPodPlaying();
  }.bind(this);
  this.player.on(dashjs.MediaPlayer.events['PLAYBACK_PLAYING'], playingHandler);
  var endedHandler = function() {
    this.onAdPodEnded();
  }.bind(this);
  this.player.on(dashjs.MediaPlayer.events['PLAYBACK_ENDED'], endedHandler);
  var logHandler = function(e) {
    this.onLog(e);
  }.bind(this);
  this.player.on(dashjs.MediaPlayer.events['LOG'], logHandler);
  var errorHandler = function(e) {
    this.onAdPodError(e);
  }.bind(this);
  this.player.on(dashjs.MediaPlayer.events['ERROR'], errorHandler);

  var customEventHandler = null;
  if (this.onCustomEventHandler) {
    customEventHandler =
        this.onCustomEventHandler.bind(this.customEventHandlerScope);
    this.player.on(SCHEME_ID_URI, customEventHandler);
  }

  this.cleanUpPlayerListener = function() {
    this.player.off(
        dashjs.MediaPlayer.events['PLAYBACK_PLAYING'], playingHandler);
    this.player.off(dashjs.MediaPlayer.events['PLAYBACK_ENDED'], endedHandler);
    this.player.off(dashjs.MediaPlayer.events['LOG'], logHandler);
    this.player.off(dashjs.MediaPlayer.events['ERROR'], errorHandler);
    if (customEventHandler) {
      this.player.off(SCHEME_ID_URI, customEventHandler);
    }
  };
};video_player.js

设置播放器事件回调

如需根据播放器事件管理广告连播播放，请创建 VideoPlayer.onAdPodPlaying()、VideoPlayer.onAdPodEnded() 和 VideoPlayer.onAdPodError() 方法：

/**
 * Called when ad stream playback buffered and is playing.
 */
VideoPlayer.prototype.onAdPodPlaying = function() {
  debugView.log('Player: Ad Playback started');
};

/**
 * Called when ad stream playback has been completed.
 * Will call the restart of broadcast stream.
 */
VideoPlayer.prototype.onAdPodEnded = function() {
  debugView.log('Player: Ad Playback ended');
  this.stop();
  if (this.onAdPodEndedCallback) {
    this.onAdPodEndedCallback();
  }
};

/**
 * @param {!Event} event The error event to handle.
 */
VideoPlayer.prototype.onAdPodError = function(event) {
  debugView.log('Player: Ad Playback error from dash.js player.');
  this.stop();
  if (this.onAdPodEndedCallback) {
    this.onAdPodEndedCallback();
  }
};video_player.js

为 `onAdPodEnded` 事件创建 setter

通过创建 VideoPlayer.setOnAdPodEnded() 方法，设置在广告连播结束时运行的回调函数。应用类会使用此方法在广告插播后继续播放内容。

/**
 * Sets a callback function for when an ad pod has ended.
 * @param {!Function} callback Callback function.
 */
VideoPlayer.prototype.setOnAdPodEnded = function(callback) {
  this.onAdPodEndedCallback = callback;
};video_player.js

处理数据流元数据事件

通过创建 VideoPlayer.setEmsgEventHandler() 方法，设置一个根据 emsg 事件运行的回调函数。对于本指南，请添加 scope 参数，因为您是在 video_player.js 之外调用 setEmsgEventHandler()。

/**
 * Sets emsg event handler.
 * @param {!Function} customEventHandler Event handler.
 * @param {!Object} scope JS scope in which event handler function is called.
 */
VideoPlayer.prototype.setEmsgEventHandler = function(
    customEventHandler, scope) {
  this.onCustomEventHandler = customEventHandler;
  this.customEventHandlerScope = scope;
};video_player.js

显示和隐藏广告插播时间点的视频播放器

如需在广告插播期间显示视频播放器，并在广告插播结束后隐藏播放器，请创建 VideoPlayer.show() 和 VideoPlayer.hide() 方法：

/** Shows the video player. */
VideoPlayer.prototype.show = function() {
  debugView.log('Player: show');
  this.broadbandWrapper.style.display = 'block';
};

/** Hides the video player. */
VideoPlayer.prototype.hide = function() {
  debugView.log('Player: hide');
  this.broadbandWrapper.style.display = 'none';
};video_player.js

接下来，创建一个广告管理器类，以使用 IMA SDK 发出串流请求、获取广告连播清单、监听 IMA 串流事件，并将 emsg 事件传递给 IMA SDK。

HbbTV 使用入门

创建广告管理器类