# How to implement preview thumbnails on Android

This article describes how you can enable preview thumbnails, which THEOplayer implements through the TextTrack API. The thumbnails are loaded as a separate text track, by side-loading them as a text track in your source description.

A demo of the preview thumbnails on the THEOplayer Web SDK is available at <https://demo.theoplayer.com/preview-thumbnails>.

## Usage

You can add or edit your source description as follows.

```kotlin
val sourceWithThumbnails =
    SourceDescription.Builder("https://cdn.theoplayer.com/video/big_buck_bunny/big_buck_bunny.m3u8")
        .textTracks(
            TextTrackDescription.Builder("https://cdn.theoplayer.com/dash/theoplayer/thumbnails/big_buck_bunny_thumbnails.vtt")
                .isDefault(true)
                .kind(TextTrackKind.METADATA)
                .srclang("en")
                .label("thumbnails")
                .build()
        )
        .build()
```

## Related articles

* [How to insert subtitles](https://docs-preview.optiview.dolby.com/pr-863/theoplayer/how-to-guides/android/text-tracks/insert-subtitles.md)