NVIDIA vs. Radeon VDPAU Mesa 17.2 Video Decode Performance
Well, I've encountered Radeon VDPAU issues before, but don't recall the performance being so severely bad. Interestingly, the older Radeon R7 260X ended up being faster than the newer Polaris/Fiji/Tonga graphics cards but the R7 370 meanwhile couldn't handle this particular test. There's either a VDPAU Gallium3D issue going on or some other issue with the Radeon stack for video decode.
So on a performance-per-Watt basis, the Radeon cards don't end up being competitive in their current form. Later in this article are some GPU thermal numbers.
With qvdpautest's 1080p MPEG decoding test, the Radeon cards were competing with Fermi and behind Kepler GPUs tested.
With H.264 decoding, the Radeon cards were all coming behind the $70 GeForce GT 1030.