I have the same issue. I'm using a HP laptop with e350 processor and AMD Radeon HD 6310 Graphics. Driver version 9.00.11-120920a-147436C-ATI (I think).
Now the thing is I have no problem at all playing full HD video but GoPro mp4 causes problem. I have set use hardware acceleration in VLC but does not help. I'm on Kubuntu 12.10.
Opening the video in AVIDEMUX (for editing and conversion) I get an alert about using b-frames as an reference that could cause instability.
Might that be it???