its likely that SL and VLC are using the integrated GPU to decode frames at the same time and its likely too much for the GPU to handle.
In fact, SL on its own is too much for the GPU. I'm getting less than 10 fps and it's jerky. Often it freezes for several seconds at a time.
I had an AMD FirePro, but it developed a memory defect, making the system crash, thus forcing me to pull out the card. Now, I'm considering getting a new graphics card, but it's a laptop and I'm not familiar with the compatibility issues. Is there a good place, like a forum, to go for assistance?
im not familiar with Linux but your problem sounds all too familiar to me.
i would think though, if you minimize SL (Firestorm), GPU use should cease from it and then VLC should work, but i dont know the implementation of firestorm on Linux though i am familiar with SL and firestorm (im an SL member for almost 20 years now)
I'm going to try the minimisation at some point.
-aw