Thanks for your help. I finally found why it did not work. Explanations for those in need.
I tried your link but I didn’t work either. Since I’m behind a proxy, Internet was not reachable. I added proxy settings in wp-config.php file, so I could display the video you sent me.
It was not the reason why I could’nt display the videos.
Since I use FTp to transfer my videos, wordpress did not include them into the database so that it couldn’t display them. I installed the plugin “Add from server ” to do it.
Finally it works, all videos are displaying
Thanks you very much for your help and for Foyer