Latest version

The latest version of the K-Lite Codec Pack that is compatible with Windows XP is:

13.8.5 - Basic/Standard/Full - Mega (2018-08-23)

Graphics driver configuration tweaks

Fix bad video playback performance with NVIDIA drivers

NVIDIA control panel > Manage 3D settings > Global Settings > Power Management Mode > Select "Adaptive" (instead of the default "Optimal")