I would recommend Hap for all video samples. I know that they can be larger files, but they will perform the best in the Sample Player. The topic of encoding can get a little bit complicated, and certain aspects of the video might change the way that you decide to encode them (for example, if you need an alpha channel). In general, lowering the framerate, for videos in the Sample Player, can be a good idea if you have high framerate videos (e.g. 50+ frames per second).