How to create a custom preset for thumbnail generation?

Hi,

I have to create a new encoding preset for Adobe media encoder for generating a thumbnail. My requirement is to create one thumbnail which is not from the first frame of the video. I have tried different parameter and going through the .epr file tags, all the time it is generating a thumbnail for the first frame. In my case, most of the video starts with some black frame for a few seconds, so for all these kind of video, the thumbnails are of the same.

Is any parameter or changes in .epr file tags to make a thumbnail at a random position or other than the first frame?