Video in the material can’t be affected with MoGraph. What can be directed are images based on brightness-values of the clones via the Multi-Shader.
The key is to have a cycle of gray values for each clone that represents the clip’s running time and move the cycles for each randomly.
For a four-second clip with a matching fps, this would be it.
If all 20 clips are added into one clip, then saved as an image sequence, this would be an option, but it would not cycle a single clip per screen, of course. Since I have not a lot of data about the project, clip length all equal, etc. I can’t say more.
Besides that, the Animation parameter Range start/end and loop will allow for a manual setting, but that is typically not wanted.
All the best