Amazon Engineer Adds LTR Encode Support To Open-Source AMD Radeon Linux Driver
LTR in this context refers to the Long-Term Reference mode with video encoding as a reference frame for "long distance" future frames. LTR encoding can be useful for quality improvements and resynchronization of the encoder/decoder for repair frames during data loss.
The nearly 100 lines of new Mesa code affect the RadeonSI Gallium3D driver's VCN video encode path as well as the Gallium3D "VA" video acceleration front-end in the context of H.264 encoding to handle LTR. Besides this merge request being notable in its own right, it's also interesting how this came about.
The RadeonSI LTR encode addition came from an Amazon.com email address and is a software engineer at the company. It also appears the engineer is either directly involved with -- or related to -- the Amazon Luna cloud gaming effort based on public LinkedIn activity.
As covered last year on Phoronix, newer Amazon Luna cloud gaming servers are apparently running Linux with making use of Wine/Proton, DXVK, and the like that was noted while they were hiring more engineers to join the Luna team. It's likely that this AMD LTR encode support for Mesa was driven for this purpose due to the benefits of LTR especially for Internet transmission of the encoded video contents, i.e. streaming the game to the client.
I haven't been able to find any current information about the hardware powering the Amazon Luna gaming servers but at least as of 2020 it was reported to be running on Amazon EC2 instances with Windows and NVIDIA T4 GPUs. Since then their Linux work server-side for Luna has become public and now there is this Amazon.com-connected RadeonSI contribution to Mesa from an engineer that appears to have ties to the Luna team. So with that it would seem Amazon may be using Radeon GPUs too now for Luna or at least exploring the possibility. Granted, that wouldn't be surprising in the least considering Google's Stadia is well known for its Linux server and AMD GPU combination, among other AMD+Linux combinations within the industry due to their well-received and fully open-source graphics driver stack. Whatever their motivation, it's always great seeing useful open-source driver enhancements.
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