Wiki:
github.com
Manual:
Stable: mpv.io
Git: mpv.io
User Scripts & Shaders:
github.com
High quality video output profile (goes into mpv.conf):
profile=gpu-hq
Configuration Files:
mpv.io
mpv.io
Input.conf:
github.com
Post your system specs and config if you're asking performance related questions.
Windows Builds:
sourceforge.net
Evaluating mpv's upscaling algorithms:
artoriuz.github.io