构建应用类

在 application.js 中，为与 HbbTV 广播互动的 HbbTV 应用创建主类。此类与 broadcastAppManager 和 broadcastContainer 进行交互。如需查看类似类的示例，请参阅处理广播音频/视频对象。

修改此基本 HbbTV 应用以请求 IMA 直播并响应广告插播事件。

初始化应用

按照教程处理广播 a/v 对象中的说明，在 application.js 中初始化应用类，设置 broadcastAppManager 和 broadcastContainer。然后，启动新的 VideoPlayer 和 AdManager 对象。

/** Main HbbTV Application. */
var HbbTVApp = function() {
  this.broadcastAppManager = document.getElementById('broadcast-app-manager');
  this.broadcastContainer = document.getElementById('broadcast-video');

  this.playState = -1; // -1 as null play state.

  try {
    this.applicationManager =
        this.broadcastAppManager.getOwnerApplication(document);
    this.applicationManager.show();
    this.broadcastContainer.bindToCurrentChannel();
    this.subscribedToStreamEvents = false;
    this.broadcastContainer.addEventListener(
        'PlayStateChange', this.onPlayStateChangeEvent.bind(this));

    debugView.log('HbbTVApp: App loaded');
    this.videoPlayer = new VideoPlayer();
    this.videoPlayer.setOnAdPodEnded(this.resumeBroadcast.bind(this));
  } catch (e) {
    debugView.log('HbbTVApp: No HbbTV device detected.');
    return;
  }

  this.adManager = new AdManager(this.videoPlayer);
};
application.js

发出 IMA 流请求

在 HbbTVApp.onPlayStateChangeEvent() 方法中，发出流请求以响应应用切换到 PRESENTING_PLAYSTATE。此方法可让您的应用准备好在响应 AD_BREAK_EVENT_ANNOUNCE 事件时加载广告插播清单。

if (!this.subscribedToStreamEvents &&
    this.broadcastContainer.playState == PRESENTING_PLAYSTATE) {
  this.subscribedToStreamEvents = true;
  this.broadcastContainer.addStreamEventListener(
      STREAM_EVENT_URL, 'eventItem', function(event) {
        this.onStreamEvent(event);
      }.bind(this));
  debugView.log('HbbTVApp: Subscribing to stream events.');
  this.adManager.requestStream(NETWORK_CODE, CUSTOM_ASSET_KEY);
}
application.js

如果设备未正确发出广播容器 PlayStateChange 事件，请使用 setInterval() 函数检查播放状态变化：

setInterval(function() {
      if (!subscribedToStreamEvents &&
            this.broadcastContainer.playState == PRESENTING_PLAYSTATE) {
        subscribedToStreamEvents = true;
        this.broadcastContainer.addStreamEventListener(
            STREAM_EVENT_URL, 'eventItem', function(event) {
              this.onStreamEvent(event);
            }.bind(this));
        debugView.log('Subscribing to stream events');
        this.adManager.requestStream(NETWORK_CODE, CUSTOM_ASSET_KEY);
      }
      …

监听 HbbTV 流事件

创建 HbbTVApp.onStreamEvent() 方法以监听广告插播时间点事件 adBreakAnnounce、adBreakStart 和 adBreakEnd：

/**
 * Callback for HbbTV stream event.
 * @param {!Event} event Stream event payload.
 */
HbbTVApp.prototype.onStreamEvent = function(event) {
  var eventData = JSON.parse(event.text);
  var eventType = eventData.type;
  if (eventType == AD_BREAK_EVENT_ANNOUNCE) {
    this.onAdBreakAnnounce(eventData);
  } else if (eventType == AD_BREAK_EVENT_START) {
    this.onAdBreakStart(eventData);
  } else if (eventType == AD_BREAK_EVENT_END) {
    this.onAdBreakEnd(eventData);
  }
};
application.js

处理 HbbTV 流事件

如需处理 HbbTV 流事件，请完成以下步骤：

1. 如需加载广告插播清单以响应 adBreakAnnounce 事件，请创建 HbbTVApp.onAdBreakAnnounce() 方法：

   /**
    * Callback function on ad break announce stream event.
    * @param {!Event} event HbbTV stream event payload.
    */
   HbbTVApp.prototype.onAdBreakAnnounce = function(event) {
     var eventType = event.type;
     var eventDuration = event.duration;
     var eventOffset = event.offset;
     debugView.log(
         'HbbTV event: ' + eventType + ' duration: ' + eventDuration +
         's offset: ' + eventOffset + 's');
     this.adManager.loadAdPodManifest(NETWORK_CODE, CUSTOM_ASSET_KEY, eventDuration);
   };
   application.js

2. 如需在广告插播期间切换到广告流播放，请创建 HbbTVApp.onAdBreakStart() 方法：

   /**
    * Callback function on ad break start stream event.
    * @param {!Event} event HbbTV stream event payload.
    */
   HbbTVApp.prototype.onAdBreakStart = function(event) {
     debugView.log('HbbTV event: ' + event.type);
     if (!this.videoPlayer.isPreloaded()) {
       debugView.log('HbbTVApp: Switch aborted. ' +
                     'The ad preloading buffer is insufficient.');
       return;
     }
     this.stopBroadcast();
     this.videoPlayer.play();
   };
   application.js

3. 如需返回内容广播，请创建 HbbTVApp.onAdBreakEnd() 方法：

   /**
    * Callback function on ad break end stream event.
    * @param {!Event} event HbbTV stream event payload.
    */
   HbbTVApp.prototype.onAdBreakEnd = function(event) {
     debugView.log('HbbTV event: ' + event.type);
     this.videoPlayer.stop();
     this.resumeBroadcast();
   };
   application.js

您现在可以在 HbbTV 应用中请求并展示 IMA SDK 广告插播时间。如需将您的应用与已完成的示例应用进行比较，请参阅 GitHub 上的 IMA HbbTV 示例。