Configuring text displayer

Default displayers

Shaka Player supports two implementations of shaka.extern.TextDisplayer which can be used to render & style content subtitles.

NativeTextDisplayer

shaka.text.NativeTextDisplayer which uses browser's native cue renderer. Shaka Player creates corresponding text tracks for text streams on the video element and provides necessary data so video element can render it. This is the default displayer when shaka UI is not used, we also use NativeTextDisplayer when using PiP and Fullscreen API of the video element itself.

UITextDisplayer

shaka.text.UITextDisplayer which renders subtitles inside of a DOM container provided to shaka. Container can be provided in 2 ways, by either a shaka.Player constructor or a shaka.Player#setVideoContainer method. This call is done automatically when using Shaka UI.

// Take your custom video container element.
const container = document.getElementById('video_container');
// Attach container using player constructor.
const player = new shaka.Player(/* mediaElement= */ null, container);
// Alternatively, pass it using dedicated method.
player.setVideoContainer(container);

Font size scaling for readability

For improved readability the option to scale text size is provided via player config.

player.configure({
   textDisplayer: {
      fontScaleFactor: 1.5,
   },
});

Note: Only supported on UITextDisplayer.

Overriding Subtitle Position

Shaka Player allows applications to override the default subtitle placement and render captions in predefined regions of the video viewport. This is useful when subtitles need to avoid UI overlays, follow accessibility guidelines, or provide a consistent layout across different content.

By setting the textDisplayer.positionArea configuration option, applications can:

• Explicitly control where subtitles are rendered on the screen
• Override the automatic or cue-defined positioning
• Update subtitle placement dynamically at runtime

The following enum defines the supported subtitle placement areas:

Example configuration:

player.configure({
  textDisplayer: {
    positionArea: shaka.config.PositionArea.BOTTOM_CENTER,
  },
});

Note: Only supported on UITextDisplayer.

Text displayer configuration

Additional configuration for the text displayer can be passed by calling:

player.configure({
   textDisplayer: {/*...*/}
});

See shaka.extern.TextDisplayerConfiguration for more details.

Custom text displayer

If none of displayers is suitable for your needs, you can prepare your own. To do that you need to implement shaka.extern.TextDisplayer interface and pass your custom displayer to shaka by calling:

player.configure({
   textDisplayFactory: (player) => new CustomTextDisplayer(player),
});

Keep in mind text displayers are used entirely for rendering subtitles related directly to the content. If you wish to display other information, i.e. stream metadata, you might consider using shaka.ui.Overlay#setTextWatermark instead.