The creation mode for the thumbnails in the Sprite. Two possible creation modes exist: generate thumbnails starting with the beginning of the video or after the first configured period. When using distance=10 and unit=SECONDS and INTERVAL_END, the first image of the sprite is from the second 10 of the video. When using distance=10 and unit=SECONDS and INTERVAL_START, the first image of the sprite is from the very start of the video, while the second image is from second 10 of the video. It is recommended to use 'INTERVAL_START' when using the sprites for trick play so that there is an additional thumbnail from the beginning of the video. Only supported starting with encoder version `2.76.0`.