A number of factors can influence the performance of MixEmergency. The following is a rough guide to some of the features that can influence MixEmergency's performance.
MixEmergency uses your computer's memory to store video frames in an attempt to optimize video decoding performance. If the memory on your computer becomes low, this can cause MixEmergency's performance to deteriorate. The level of memory used can be set in the Advanced panel of the preferences. You can check the level of your computer's free memory using the Activity Monitor application on Mac OS X.
If using GPU-accelerated video decoding, make sure that MixEmergency's cache size is set to a lower value. Often a good setting is to set this at around 1/4 of the RAM available to the GPU. For example, if your GPU has 1024 MB of RAM, set MixEmergency's Cache Size to between 200 MB to 300 MB. Higher values may degrade performance.
The quality slider in the Output panel of the preferences can be used to tune performance. For example, if you were to output MixEmergency to an external screen of size 1280 x 720, and your videos are of size 640 x 480, then setting the Quality slider to medium would be appropriate. This would cause MixEmergency to render internally (transitions and effects) at 640 x 480 instead of 1280 x 720, and should improve performance while maintaining the quality of your videos. You can use the Info window to determine the output dimensions, and the quality adjusted dimensions (i.e. the render pipeline dimensions).
Some of the more complex transitions and effects can have an effect on performance. You should test your system with all the effects and transitions that you plan to use in a live situation beforehand.