Hello Enheca,
and thank you for your reply!
Sure. I try to explain the better i can.
The first occurrence of this behaviour came when I tried to export a Learning Object from one installation of Xerte (3.

to another installation (3.10) both installed on my same computer.
The export/import process went on correctly apparently. But when I opened the LO in preview mode on the new installation (3.10) and i browsed the-ages to arrive to one of those containing any video the video didn't show up and in response i obtained the request to download a file with a name apparently similar the last part of the video url. All videos are video from youtube.
This happens regardless the way I added videos to pages.
This is what I know and i can describe of the issue.
Actually I am trying a new installation on a public server to see how it goes there.
Thank you for your interest in this reported issue.
Fabrizio