I've created a link to a video file (mov) in an article. It seems to work but get teh message (in dutch) that I need to give permission to joomla to run a quicktime player file. If so how do I do that ? I can't find anything in the documentation on this.

This is a security notification from the browser. Quicktime always requires your permission to run on sites. This is the default behaviour and it is unrelated to Joomla! or your site in general.
To enable it simply click on the allow button.