Hi Pilou, yes that's normal - the forum only resizes image elements and the video is an iframe element, not an image element.

You can also view it at:
https://www.screencast.com/users/MoI/folders/Camtasia%20Studio/media/5d54cfd1-206a-449a-ba84-cd9f40e4f6c7

that one will have a "full screen" control in the lower right corner, I think it should fit it to your monitor size.

- Michael