An other notice :
Notice: Trying to access array offset on value of type bool in /home/nicefict/www/wp-content/plugins/rdv-timetable/lib/views/schedule.event.php on line 42
I think, I’ve found the reason why cover images wasn’t diplayed in the player.
SSP player use the thunmbnail version of the cover. (auto generated by WP)
Size of thumbnails can be set in “Settings/Media” in WP menu.
Thumbnail size, width and height, must be set to more than 300 each.
It should be better if SSP have is own thumbnail file for each image uploaded in WP.