Any idea why I am getting a black border around retimed frames? The net result is a black flicker around the border area between retimed and non-retimed frames. This is very annoying.

Hi,
 
Could you let us know what is your version of Retimer? Does these artifacts occur while using mattes?
We noticed this kind of mistakes in older versions but as far as we know they are fixed in the latest release 2.5.5.
 
Another possibility is that your original footage has a black margin that is distorted due to the retiming process. Black borders should always be removed from the original sequence prior to a retiming.
 
In order to answer more precisely, could you send us details on your configurartion and how to reproduce these errors: pat@realviz.com