Depending on the aspect ratio of your videos and output display, or the Scaling method that you have selected in MixEmergency's Preferences, a video may show black bars around the top and bottom, or left and right, edges. In MixEmergency, there is a simple way to avoid this without having to edit the original video file...
At the bottom of MixEmergency's Overlays window, there is a section titled Border Fill. When this is enabled a special filter is applied to any video that doesn't fit correctly into the output display's aspect ratio.
The example above shows the Blur filter applied to the video, which fills the area previously coloured black with a blurred version of the edges of the video.
There are a number of different filters that can be selected - so you can pick your favourite, or change during your mix to keep things interesting.
This tip was created with MixEmergency 2.6.0 and Mac OS X 10.9.3. Subsequent versions may differ.