I recently updated Windows Player from version 2 R201 to R257.2 and all the animated GIFs no longer work. None of the CMS files were changed so there is something that changed in the player.
One post showed that these are no longer supported which is a shame. The work around they posted showed to use a text box with an embedded picture. If this is the way that it is to be done, what URL should be used to reference an image in the Media Library?
As a feature request I think that support for animated GIFs should be reinstated.