Add preview thumbnails (Android v3)

Add preview images that appear when a user hovers over the control bar or seeks through a media asset.

JWP supports the loading of preview thumbnails for individual shots or scenes in a video. These thumbnails are displayed in a tooltip when a viewer hovers the control bar.


Preview thumbnail appearing on top of a media asset.

Preview thumbnail overview

In the Android SDK, you define your preview thumbnails in a single .vtt file. The .vtt file is part of a thumbnail Caption that is assigned to a PlaylistItem.

For an optimal user experience, the thumbnails should adhere to the following:

  • URLs must point to individual thumbnail files (filename.jpg) or to the spacial media fragment (filename.jpg#xywh=0,0,120,90) in a thumbnail sprite
  • URLs must be relative to the .vtt file
  • Thumbnail width of 100-150 px


00:00.000 --> 00:02.000

00:02.000 --> 00:05.005

00:00.000 --> 00:02.000

00:02.000 --> 00:05.005


When a media asset is uploaded to your JWP account, a thumbnail track file is created as part of the transcoding process. So, instead of creating a new .vtt file for a video asset, you can copy the URL of the thumbnail track file from your JWP dashboard.

To locate the thumbnail track of a specific video asset, follow these steps:

  1. From the video list page, click the name of a video.
  2. On the ASSET tabs, scroll down to Tracks section.
  3. Click the Thumbnail track row.
  4. Copy the Direct Link URL.

Adding preview thumbnails to an app

  1. In your main activity, create a List<Caption> object and name it, for example, thumbnailTrack.
  2. Create a Caption object and name it, for example, previewThumbnail.
  3. In the Caption object, define the preview thumbnail .vtt file URL (file). You can use the .vtt file mentioned in the TIP box above that JWP creates during the transcoding process.
  4. Define the Caption object as a thumbnail track (kind(THUMBNAILS))
  5. Add previewThumbnail to thumbnailTrack.
  6. Add thumbnailTrack to a PlaylistItem object.
List<Caption> thumbnailTrack = new ArrayList<>();

Caption previewThumbnail = new Caption.Builder()

PlaylistItem playlistItem = new PlaylistItem.Builder()
    .title("Playlist-Item Title")
    .description("Some really great content")
List<PlaylistItem> playlist = new ArrayList<>();
PlayerConfig config = new PlayerConfig.Builder()