[Snippo]

Here are the logs. Pastebinit didn't work for some reason so I used something different.

kodi.log:
http://pasted.co/5dfef35e

dmesg:
http://pasted.co/38554646

journalctl -S "today":
http://pasted.co/ba9158fb

vainfo:
http://pasted.co/8e35e315

The drops only start after about 20 seconds, which can also be seen in the debug log.

Edit:
and pacman -Qs mesa:
local/glu 9.0.0-4
Mesa OpenGL Utility library
local/libtxc_dxtn 1.0.1-6
S3 Texture Compression (S3TC) library for Mesa
local/mesa 11.1.2-1
an open-source implementation of the OpenGL specification
local/mesa-demos 8.3.0-1
Mesa demos and tools
local/mesa-libgl 11.1.2-1
Mesa 3-D graphics library

Let me know if I forgot something.