Our VDPAU testing had not stopped after looking at the CPU usage. Instead of just showing the CPU usage results, we also recorded a video of playing back the H.264 1920 x 1080 with and without VDPAU -- but here's the catch: we did this while we were compiling the Linux kernel (by running phoronix-test-suite benchmark build-linux-kernel). Due to the single-core Sempron being occupied with compiling the kernel using multiple jobs simultaneously, the CPU utilization was already at 100% when starting our video playback testing.
Above is the MPlayer playback of the video without VDPAU. To take note of in the video is particularly the choppy audio (especially starting halfway through) since the CPU is busy with GCC compiling the Linux kernel. Below is the video when VDPAU was enabled.
There still were a few areas where the video playback had slowed down with VDPAU, but the audio was remarkably better and it was a much-improved experience -- it's certainly not bad for compiling the Linux kernel simultaneously all with a $20 processor and $30 graphics card.