AMD's X-Video Bitstream Acceleration

In early September we shared that UVD2 and XvMC is coming to Linux and that two new library files had begun shipping with the ATI Catalyst driver: AMDXvBA and XvBAW. Earlier this month the Unified Video Decoding 2 (UVD2) support was then enabled by default in the Catalyst 8.10 driver. These video acceleration improvements to the ATI Linux driver aren't exactly end-user friendly yet, but today we have information on how those interested can begin using the X-Video Motion Compensation extension with their ATI hardware along with what the XvBA extension will provide users in regards to advanced video acceleration that is very similar to Microsoft's DirectX Video Acceleration.

Earlier this month we had toyed around with the XvMC wrapper and making other changes to the XvBAW library in order to use XvMC with the binary ATI Linux driver. Those efforts were to no avail, but if you recompile mplayer and specify the ATI XvMC library, you should be able to use this extension. From the mplayer source-code run configure with the --enable-xvmc and --with-xvmclib=AMDXvBA arguments. Check your Xorg.0.log to ensure that the Unified Video Decoder 2 is enabled.

XvBA isn't yet usable by end-users on Linux, but we have acquired some information on this UVD2 video acceleration interface. XvBA stands for X-Video Bitstream Acceleration and it's very similar (if not identical) to DXVA. DXVA, or DirectX Video Acceleration, is Microsoft's video interface that allows the GPU to accelerate iDCT, motion compensation, de-interlacing, and color correction. XvBA also supports accelerating all of these operations. XvBA is mirrored off DXVA since all of their hardware takes DXVA formatted packets so it was easiest and most efficient to model this Linux video acceleration interface after what they are doing on Windows. Now most of the multimedia source-code to the Catalyst driver is shared between Windows and Linux. Initially, XvBA will accelerate H.264, VC1, and MPEG-2 formats.

Right now this XvMC and XvBA support is limited to those with UVD2 graphics cards (primarily the Radeon HD 4000 series), but AMD may backport the XvBA interface to earlier UVD1 chipsets. Backporting the XvMC MPEG-2 support is less likely to happen. XvBA will be able to accelerate more than one video at a time and there are no limitations such as needing root access. The API for XvBA isn't published yet and we are not sure whether it will be due to legal issues. We're told by a credible source though that X-Video Bitstream Acceleration wouldn't be much of a challenge to reverse-engineer by the open-source community.

We have found out that early on in the XvBA development they had looked at VA-API but as aforementioned, they wished to follow a similar design to the DirectX Video Acceleration design. Earlier this year at FOSDEM it was talked about by Intel's Keith Packard to extend XvMC to support more formats. This hasn't been done yet but as of September at XDS, Keith still intends to do this as a stopgap solution until VA-API is ready. The UVD2 XvMC implementation only accelerates MPEG-2 video.

When we have more information on X-Video Bitstream Acceleration (XvBA), we will pass it along. The changes required by mplayer (and other Linux video applications) to implement XvBA are fairly invasive, so it may be a while before end-users are exposed to this level of acceleration.