Friday, December 9, 2011

Picking the Right Driver

We are very excited to announce the availability of the fourth generation G-Series 1 VP8 hardware decoder, internally codenamed “Driver”.

In this release, our focus has been on optimizing the VP8 bitstream decoder. The new architecture helps the IP run at 13% higher operating frequency allowing the decoder chips to reach higher frame rates or do multi-channel decoding more easily. At the same time, the new implementation has reduced the decoder’s logic gate count by 6% which directly cuts the production cost of each chip incorporating a WebM hardware decoder. Furthermore, the revamped design allows us to do even more optimizations for the next release. With future video requirements in mind, we designed Driver to decode up to 4k by 4k video resolutions.

To make the IP evaluation easier for a chip company, the deliverables now include a bit-exact decoder C-model. This allows partners to create their own test cases for thorough performance analysis.

Modern multi-core CPUs are getting powerful enough to decode HD video, so why is having hardware accelerators still useful? One good reason is battery life. We got our hands on one of the first commercial Android tablets based on the Rockchip RK2918 chip which uses our very own WebM hardware decoder and ran some tests. We charged the battery and looped a 480p video until the battery died. For the purpose of the experiment, we had to limit the resolution because the single-core CPU of the device could not run 720p @ 30fps in pure software. The battery test was done with the VP8 hardware acceleration enabled and disabled, and at two display brightness settings. The result: with the hardware offload the battery lasted up to 36% longer which gets us one extra movie to watch on that long flight! You can see the battery discharge vs. elapsed time plots below. Needless to say, using two or four CPU cores for HD video decoding in software uses even more power and widens the gap to hardware's benefit.

The G1 v4 VP8 decoder is now available for licensing at no cost at the WebM Project hardware page. The multiformat version of the IP and support services can be accessed through our partner Verisilicon.

Aki Kuusela is Engineering Manager of the WebM Project hardware team.

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