[CinCV] need clarification of user-manual comment

In section 3.3.4 under limitations of the open-gl playback driver the following statement exists:

Project and track sizes need to be multiples of four for OpenGL to work.

Can someone clarify?  this statement can be taken several ways. 1) do you mean that the length of the clip must
be a multiple of four?  2) do you mean that the frame image dimensions must be evenly divisible by four? 3) do
you mean that the visuals in the timeline must be sized somehow?

What is it that you're trying to say here?

regards