4:3 content does not display properly when playing or pausing. The player seems to be getting some kind of re-sizing information that incorrectly adds a letterbox effect. The best way to identify the problem is to show how the interlacing fields are crushed slightly, highlighting how the output is distorted. There is problem with the 16:9 content.
I have done a great deal of testing and cannot find the source of this issue. At first I thought it related to video.js or css, but at this point I believe it is a bug in the video field. I have verified that the transcoded content has the correct dimensions and, since the problem shows up when using mediaelement.js player, it can't be a video.js issue. I am using multiple content types, one for HD (16:9), one for NTSC (4:3), and one for PAL (4:3).
Attached are two screen shots and the poster frame for a PAL 4:3 example, and a screen shot for a NTSC 4:3 example.
For what it's worth, PAL clips have 7 pixels of black added to the top and bottom of the player, and NTSC clips have 5 pixels added to the top and 6 pixels added to the bottom.