Given the difference seen between HD (720p) and SD video, I suspect your CPUs are not powerful enough to show the HD videos smoothly.
Can you verify that hardware-accelerated direct rendering is enabled? - please provide the output of glxinfo |grep render on each system.
Also, on the NVIDIA 8400 GST if may be possible to enable VDPAU if it is not already enabled.
Given the difference seen between HD (720p) and SD video, I suspect your CPUs are not powerful enough to show the HD videos smoothly.
Can you verify that hardware- accelerated direct rendering is enabled? - please provide the output of glxinfo |grep render on each system.
Also, on the NVIDIA 8400 GST if may be possible to enable VDPAU if it is not already enabled.