Transcode Performance: The APU, CUDA, Stream, And Software
Limited to decode acceleration, our expectations of what AMD’s Zacate APU will be able to do in transcode-oriented workloads has to be tempered.
We’re testing each solution with a 10.5 Mb/s trailer of the movie Death Race from Apple’s Web site, encoded using H.264 video and AAC multi-channel audio.
Because the E-350 doesn’t include hardware-accelerated encode, we’re only able to test it in software-only mode and with decode acceleration enabled. Using an optimized copy of CyberLink MediaEspresso 6.5, and converting to the canned iPad profile (Smart Fit, H.264, AAC) we cut what would have been a nearly 11-minute transcode down to just over nine minutes—an almost-20% speed-up.
AMD’s 880G chipset, armed with Radeon HD 4250 graphics (40 stream processors) is similarly too anemic to handle encode acceleration. That task rests on the low-power Athlon II X2 240e running at 2.8 GHz. As a result, we’re able to compare software transcoding to AMD’s chipset with decode acceleration enabled. Because the desktop-class CPU is so much faster than Zacate, even the software-based test blazes by in less than four minutes. Decode acceleration helps get the job done 17% faster, though.
In software-only mode, Intel’s 10 W Celeron SU2300 takes more than eight minutes to complete its transcode task. Flipping the switch on Nvidia’s Ion chipset, enabling PureVideo support, helps cut that number to just over seven minutes. Adding hardware-accelerated encoding makes an even more dramatic impact, cutting the transcode to less than four minutes. All told, you get a 212% performance boost by turning on hardware-accelerated encode and decode.
Now, the most interesting result surfaces when you switch off decode acceleration, leaving accelerated encoding enabled. The job drops to 3:45, 14 seconds less than decode/encode enabled. Why is this? As it turns out, if you ask Ion to handle both encode and decode, the decode side of that equation slows down, causing the fully-accelerated configuration to take longer than if you let the CPU handle decoding on its own.
If you’re using a mobile system, you’ll still want to leave both hardware options turned on, though, because you’ll benefit from reduced host processor loading with full acceleration enabled, and consequently, longer battery life.
Despite its Ion chipset, the Atom-based platform does not show CUDA acceleration as an option in MediaEspresso. As such, we were only able to select PureVideo decode acceleration. But as the results demonstrate, that doesn't help our transcode job at all. In fact, the data transfer from graphics to processor is enough to slow down the workload versus a software-only implementation.