Thank you for your answer – I see the problem, but I don′t know how to solve it.
I have NOT used an extra iframe, I used the video upload function which wordpress offers by default.
I don′t see where I have to put the width on 100%, as the media-player has a default, small width.
Do you mean that the solution is NOT to use the wordpress video upload function? That I only can use an iframe and set the width on 100%?
