Is it possible to “put” an object over a video presentation in the video tag?
I have an external object (a countdown timer of the video) and I want to put it over the video (like ads i.e.).

I’ve tried with this code, but the timer goes just after the video, not in.
<video id="video1" controls autoplay ><div id="time"></div></video>
Yes, just use CSS positioning. For example, you could make the tag use relative positioning, and then position the absolutely and you can place it within that video box anywhere you wish.
I would probably put the timer outside the video though, as a sibling element, and contain them both within something else that had position relative though: