Full screen videos get stretched to fill the whole screen

[tinvsworld]

When I put a video into full screen on some sites (like kshow123, dramacool, goplay.anotpp) it gets stretched to fill the whole screen, it doesn't maintain the video's aspect ratio. I don't have these issues in chrome, safari, or firefox. Is there a way to fix this? Tried searching but can't seem to find an answer!

stretched video:

normal: