ThumbnailSet
data class ThumbnailSet(val width: Int? = null, val height: Int? = null, val interval: Duration? = null)
The pictures a stream carries for a seek bar's preview (#433): a DASH adaptation set of thumbnail tiles, an HLS image playlist, or a WebVTT thumbnail file the item names in MediaItem.thumbnails. Each image is a grid of tiles, one tile for each stretch of time. Tracks.thumbnails lists the set, and KitePlayer.thumbnailAt gives the tile for a position.