# Preview thumbnails
Show preview thumbnails when hovering the seek bar, sourced from the manifest or a side-loaded WebVTT track.
Tip: open your browser's developer console and use the `player` and `THEOplayer` variables to interact with this demo.
**Thumbnail source**
In-manifest (DASH tiled thumbnails)Side-loaded (WebVTT)
Hover or scrub the seek bar to see the preview thumbnails.
DASH streams can carry tiled thumbnails inside the manifest. For streams without them, you can side-load a WebVTT file whose cues point at thumbnail images: add it as a `metadata` text track labeled `thumbnails` and the player's seek bar picks it up automatically.
```js
player.source = {
sources: [{ src: 'https://example.com/video.mpd', type: 'application/dash+xml' }],
textTracks: [
{
default: true,
src: 'https://example.com/thumbnails.vtt',
label: 'thumbnails',
kind: 'metadata',
},
],
};
```
See the [preview thumbnails guide](https://optiview.dolby.com/docs/theoplayer/knowledge-base/playback/what-are-the-benefits-of-preview-thumbnails.md).
Code
demo.html
```html
Preview thumbnails
```