> [!NOTE]
> **Note:** Before moving forward with this guide, you must complete the steps in [Get started with IMA SDK on HbbTV](https://developers.google.com/ad-manager/dynamic-ad-insertion/sdk/html5/hbbtv.md.txt).

In `video_player.js`, define a video player wrapper class to initiate and
control the dash.js player.

## Set up the broadband player

Define where in your app to place the broadband player by creating video and
wrapper tags:

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

## Create the video player

Initialize the video player class with variables for HTML elements, the dash.js
player, and callbacks that other class methods can use.

```javascript
/**
 * 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');
};
```

## Define the playback control functions

To show the ad player and attach the video view, create the `VideoPlayer.play()`
method. Afterwards, create the create `VideoPlayer.stop()` method to handle
clean-up after ad pods finish.

```javascript
/** 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();
};
```

## Preload the ad stream manifest

To verify ads are sufficiently loaded during the content stream and before the
ad break begins, use `VideoPlayer.preload()` and `VideoPlayer.isPreloaded()`.

### 1. Preload the ad stream

Create the `VideoPlayer.preload()` method to preload the ad stream manifest and
build up an ad buffer prior to an ad break. You must update the player streaming
settings `'cacheInitSegments'` to `true`. By updating the settings, you enable
caching the init segments, which avoids delays when switching to ads.

```javascript
/**
 * 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');
};
```

### 2. Check the preloaded ad buffer

Create the `VideoPlayer.isPreloaded()` method to check if enough ad buffer has
preloaded compared to a buffer threshold set in the app:

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

```javascript
/**
 * 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;
};
```

## Attach player listeners

To add event listeners for the dash.js player event, create the
`VideoPlayer.attachPlayerListener()` method: `PLAYBACK_PLAYING`,
`PLAYBACK_ENDED`, `LOG`, and `ERROR`. This method also handles events for the
scheme ID URI, in addition to setting the clean-up function to remove these
listeners.

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

```javascript
/** 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);
    }
  };
};
```

## Set player event callbacks

To manage the ad pod playback based on player events, create the
`VideoPlayer.onAdPodPlaying()`, `VideoPlayer.onAdPodEnded()`, and
`VideoPlayer.onAdPodError()` methods:

```javascript
/**
 * 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();
  }
};
```

## Create the setter for the `onAdPodEnded` event

Set a callback function that runs when an ad pod ends by creating the
`VideoPlayer.setOnAdPodEnded()` method. The app class uses this method to resume
the content broadcast after ad breaks.

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

## Handle stream metadata events

Set a callback function that runs based on emsg events by creating the
`VideoPlayer.setEmsgEventHandler()` method. For this guide, include the `scope`
parameter, as you evoke `setEmsgEventHandler()` outside of `video_player.js`.

```javascript
/**
 * 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;
};
```

## Show and hide the video player for ad breaks

To display the video player during ad breaks, and hide the player after the ad
break finishes, create the `VideoPlayer.show()` and `VideoPlayer.hide()`
methods:

```javascript
/** 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';
};
```

Next, create an ads manager class to use the IMA SDK to make a stream
request, get an ad pod manifest, listen to IMA stream events, and pass emsg
events to the IMA SDK.