The font size for the File Name at the top of the light box view of the Media Viewer is too small compared to the Author and Source Names below it, as seen on this multimedia alpha site. (1)
Consider increasing the font size for that File Name, as proposed in our design team's mockup (2).
Also, we should aim to let that title stretch all the way to the right of the page, instead of wrapping it up in the middle, as shown in the attached screenshot.
More info about Media Viewer on our project page (3).