Without any system information and details like e.g. how your hardware acceleration is configured, your cache and so on we can't really tell you much. To me it sounds perfectly normal that on a weaker system you video goes stuttery. Even if the actual hardware accelerated decoding of e.g. an MP4 video may work smoothly, there could simply be other issues that show up at full res like VSync tearing or your disk cache not being able to keep up. Either way, more info is required for a reasonably certain asessment of the situation.