For technical reasons, I have disabled the ability to upload video to the media gallery. It wasn't supposed to be possible yet anyway! I will be working on a solution which is more usable and flexible and will aim to roll that out soon after we upgrade to the new version of the website in coming months. This change won't affect existing videos already in the gallery - I'll deal with them separately once I get the new solution operational. Please note that for now, you will still see the option to upload videos in the gallery - and you will even be able to select a file and actually upload it, but then it will fail with a message about the video file type not being allowed.