VC-1 Encoded Playback
VC-1 is the most common codec in the first wave of HD-DVD and Blu-ray discs that were released in the US, and is actually the basis for the Windows Media Video 9 codec as well. The bit rates on our VC-1 discs averaged in the 12-15 Mbps range though it can top out at 20 Mbps in some places.
I watched quite a few movies encoded with VC-1 with the bit rate information on screen in order to find a title that seemed to use higher bit rates that most (as more advanced/proper VC-1 implementation will lead to higher rates). I went with the new Mission: Impossible III video for our benchmarking, starting in the fourth scene and recording CPU utilization data for 3 full minutes. Lower CPU utilization means a better user experience and leaves more CPU cycles for other tasks that might be going on in the background in the operating system. We tested with and without hardware acceleration enabled, effectively testing CPU decoding versus CPU and GPU combined decoding.
From our testing, average CPU utilization is 10% lower when we enable the NVIDIA PureVideo HD technology for decode acceleration.
H.264 Encoded Playback
I was more interested in the newer, more compute-intense H.264 codec that more and more movies will be released with in the coming months. This codec offers a higher image quality with similar storage levels but requires more processing to decode quickly enough for smooth playback. In our testing the H.264 bit rates were higher than the VC-1 rates, in the high 18-19 Mbps up to 22 Mbps in some cases. The codec itself is already speced at bit rates up to 960 Mbps (!!) though we obviously don’t have the power to decode that quite yet.
Our first HD-DVD tested is “True Blue” a film that looks at ocean wildlife, beaches and other places that we’d all rather be. The imagery and great range of colors created a GREAT visual quality test as well as performance test with its H.264 encoding. As you can clearly see, the E6400 processor is having a difficult time decoding the movie with the CPU usage basically spiked at 100% the entire time the movie is playing. Dropped frames were very common and I can easily say that in this mode, watching an HD-DVD would definitely be a bad user experience.
However, once we enable the hardware acceleration in the PowerDVD control panel, things are much improved. Average CPU usage drops from 99% to 55% and maximum and minimum rates waver within 10% either way. The movie experience was MUCH better and I was able to watch the whole movie without any hiccups or dropped frames of any kind. Plus, with only 55% CPU utilization, we theoretically have some spare head room for additional applications.
The first retail HD-DVD with H.264 support in the US uses a slightly lower bit rate that “True Blue”, but “The Interpreter” is still a much more difficult movie to decode than the VC-1 titles with CPU utilizations in the 80% range on average without the NVIDIA PureVideo HD hardware acceleration. When we flip the hardware switch, CPU usage is cut in half and the experience is much smoother and we have room for more processing if necessary.