when I start VLC like this:
export LIBVA_DRIVER_NAME=gallium
vlc
and then inside VLC select VA-API as hardware acceleration and then open a
video, my screen goes black after a few seconds and my system becomes
unresponsive and I have to force poweroff by long pressing the power button.

I am using Arch Linux with the 3.18.2 Kernel and Mesa 10.4.2
My graphics card: Advanced Micro Devices, Inc. [AMD/ATI] RV610/M74 [Mobility
Radeon HD 2400 XT]