mpeg2 is not accellerated with xvba, h264 l5.1 is also not possible with xvba. if you select other testfiles xvba should work. in theory there is a h264 encoder you can use via (intel) vaapi es well but i don't know if there is an app using is yet (besides the test tools from libva).
GMA3150, with free drivers, versus Brazos, with free drivers, and with less than 1/10 of its theoretical performance, thanks to crappy free drivers.
I think it's perfectly possible. Brazos only wins over GMA3150 when using Catalyst.
And that'd be delusional, The Atom N series is paired with the 200Mhz version of the GMA3150, so thats 2 200Mhz OpenGL2 Pixel Pipelines and only support for MPEG2 acceleration vs 80 280Mhz OpenGL4.2/OpenCL1.1 shaders, even at 1/10th optimal performance the GMA3150 a POS. Especially when you look at the CPUs, the AMD Z-01 and C-50 are both real dual core 64-bit CPUs at 1Ghz, All the Pineview series save for the 2 top end N550 and N570 are single core with hyperthreading and as such they are the only ones that come close to the E-350, E-450 and E2-1800 in terms of raw CPU power.
As for MPEG2 performance, it's still not all that relevant since my decade old Pentium4 can handle it. Just rip your DVDs already, the optical drive is eating more of your battery on the current crop of low end CPUs.