ATI Stream GPU assisted video transcoding – meh?
ATI has released new drivers that has unlocked what they call ATI Stream accelerated video encoding. Basically, if you have an ATI 46xx or 48xx series card, then the powerful stream processors onboard can now be used for tasks usually reserved for CPUs, such as video encoding. This is basically a late response to Nvidia’s CUDA, which does the same thing.
Included as a separate downloads, the free ATI Avivo Video Converter supports this new type of acceleration, which is very useful because it is the only software that supports it at the moment.
So I decided to test encoding performance in ATI Avivo Video Converter using version 8.11 (no accelerated encoding using ATI Stream) and 8.12 (supports ATI Stream), and to see whether there’s a difference.
First up, not all the encoding profiles support ATI Stream. The iPod, PSP, DVD and DivX ones do (some of others may as well, but I didn’t test all of them), and so I decided to test DVD and DivX encoding (the other two types had similar results).
A bit more details about the test setup:
CPU: Intel E8500
RAM: 4 GB DDR3
GPU: ATI Radeon HD 4850 (512 MB)
OS: Windows XP SP3
The input file:
Type: XviD (AVI)
Length: 21 minutes
Size: 175 MB
The output profiles used:
DVD: Max bitrate (8 Mbps)
DivX: Max bitrate (2.6 Mbps)
First up is version 8.11, the one without ATI Stream support. Here are the results:
DVD:
Conversion Time: 2:08
CPU Usage: 100%
GPU Usage: 0%
DivX:
Conversion Time: 1:39
CPU Usage: 100%
GPU Usage: 0%
Now for version 8.12 results, where ATI Stream support is now activated:
DVD:
Conversion Time: 2:03
CPU Usage: 100%
GPU Usage: 0 to 15-20%, intermittent
DivX:
Conversion Time: 1:36
CPU Usage: 100%
GPU Usage: 0 to 15-20%, intermittent
Pretty underwhelming, you have to say. Only a 3 to 4% increase in encoding performance, which is not surprising because the GPU was hardly used during the whole thing. Nvidia’s CUDA takes a different approach, using more GPU, but less CPU, even if the encoding takes a little longer (more on that later). As a first attempt, it’s not great, but at least it shows that ATI is moving in the same direction as Nvidia and future applications from Cyberlink or TMPG Inc (which already supports CUDA acceleration) might yield better results.
As for the ATI Avivo Video Converter, the application is pretty easy to use, but unfortunately, the output quality as well as the profiles provided are fairly poor. And if that’s not bad enough, you are limited to only the selected profiles and with only bitrate as the only adjustable option (and even then, it’s limited to quite low values). The encoding speed, even without acceleration, is pretty quick as a result, about 12 minutes to encode a DVD compliant MPEG-2 file for your typical 120 minute movie. If you don’t care about quality, and want to at least get your GPU to do a little bit of the work, then this might be the tool for you.
For everyone else, it’s best to wait until a proper encoder comes out with ATI Stream support to see how much of a speed improvement there is, especially if it can get 100% of the core working on it.
December 14th, 2008 at 5:52 pm
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December 31st, 2008 at 9:08 pm
Strange and disapointing results. We were told that since 8.12 we’ll have real hardware acceleration – before that it was only software transcoding. As we see, we still have sofrware only transcoding (and I tryed it – GPU usage is low, only CPU is 100%).