Is the krpano version and the videoplayer plugin version up-to-date?
In older versions the scaling of the html5 video element was done via DOM-sizing and this way the browser was always scaling the video content proportionally, but in the newer versions krpano is scaling the video via CSS3D transforms, there the video can be any size.
Additionally - do you get the same results in all browsers?
Firefox has some CSS3D rendering bugs, especially when the CSS3D elements will be rendered without hardware acceleration.
Best regards,
Klaus