Consecutive Image Creation from Video

[viking]

I have a lot of videos and a single thumbnail of the video is not adequate to realize its content. It would be great if XnView could read and save consecutive images from the video:

XnView can currently build thumbnails for videos and it creates a single thumbnail with 4 images captured somewhere in the video.
1. At what times in the video are these captured?
2. I would like to have control of the timing; e.g. every 30 sec.
3. Furthermore, I would like to have the option for XnView to automatically create separate images of the video (and save them in the source folder); e.g. every 30 sec and 20 images.


Meanwhile, does anyone know of some software that can accomplish this? It needs to scan all folders and automatically create images of all videos?
(PotPlayer can capture consecutive images but it needs to play the video so it becomes very slow. It can also not scan all the folders, looking for videos)