DPS do not support looping the video however you can achieve this by a trick but it will bit raise the size of folio depending upon the video size.
- Export the video into image sequence
- Call the image sequence instead of video and set loop as per your convenient.
You could also try using a nested overlay slideshow that alternates between the video and a still from the first/last frame of the video.
If you want something to appear on top of an overlay you can try this technique