Distracting grey borders while playing videos in the Xbox Video app. Any fix?

[Makm]

While playing videos in my xbox video app there are thin grey borders at the top and bottom of the videos. The videos doesn't play in full fullscreen mode (thats what it seems like). Is there any way to fix this issue? Its disturbing for me, the grey borders are distracting.

P.S - The videos which i play has an aspect ratio of 16:9, so I'm sure its not the video which is causing this.