YouTube finally has a fix for their HD videos having black bars on the sides.
 

I started uploading high definition (HD) clips to YouTube since that become possible. My current native resolution is 1920x1200. All the clips I (and others) uploaded at this resolution, even though high definition, still had two thick black bars on the left and right sides of the video. This was just insane and unprofessional. Finally, after some time I was able to find a solution. Funnily, it's an official YouTube one - proving that it is an issue on their side. At least it's simple and can be retro applied to existing videos. All you have to do is add yt:stretch=16:9 to your tags. That's it - problem solved.


Now the video properly fills the whole space: