If you are having difficulty playing the video smoothly, here are a few tips:
When in fullscreen, click the "scaling" to OFF. This will toggle between filling your entire monitor and playing the video back at "100% size"
Press play to begin the buffering process, then immediately press pause. Let the program buffer (the gray bar filling in the timeline) for a minute or so before pressing play again. This is especially helpful on slower connections where the playback may catch up to the buffering.
As a last resort, turn the HD off. The quality is still quite good!