[Prism] Does emulated DXVA2 and DXVA11 video decoding get ANY hardware acceleration on ARM?

Thanks Jay. So just to clarify (correct me if I'm wrong), an emulated x64 program can NOT access any harware accelerated video decoding at all, regardless of whether it uses DVXA2 or DXVA11 or whether it attempts to find a hardware-enabled MFT video decoder; therefore the only way to get hardware accelerated video decoding is to compile the program as a native ARM program that looks for a hardware-enabled MFT and uses that, or uses DXVA11 (Direct3D 11) calls directly - is that correct? And if the native ARM program tries to use DXVA2 that will only run on the CPU without h/w accel?

Regarding video ENcoding, am I right to assume that emulated programs will not be able to do hardware accelerated encoding at all - in fact it will not even be able to do any encoding on the CPU because there are no encoders available on the platform for it to load. But if the program is compiled for ARM then it will be able to find and use the Qualcomm hardware-enabled video encoder?

(Presumably the Qualcomm encoder will be native ARM, so an emulated program would not be able to load it anyway?)

Is that all correct?

Hi @appleton ,

Thank you for your response. Your explanation is mostly correct; however, I think some details are still not exactly accurate. I will restate and confirm:

According to Microsoft official documentation:

1. Situation 1: “An emulated x64 program cannot access any hardware-accelerated video decoding at all; therefore, the only way to get hardware-accelerated video decoding is to compile the program as a native ARM build.” I agree with you, with the caveat that this is implied by driver/architecture restrictions rather than stated explicitly How Emulation Works on Arm;
2. Situation 2: “If the native ARM program tries to use DXVA2, that will only run on the CPU without hardware acceleration.” This is only true if the hardware/driver does not support DXVA2 (and only supports newer Direct3D 11 video decode paths). Driver capability must be verified for that device About DXVA 2.0 GitHub Moonlight Docs - Hardware Decoding Support
3. Situation 3: “Regarding video encoding, emulated programs will not be able to do hardware-accelerated encoding; if the program is compiled for ARM it will be able to find and use the Qualcomm hardware video encoder (the Qualcomm encoder is native ARM, so an emulated program would not be able to load it).” Correct in principle. Hardware encoder MFTs are architecture-specific; an ARM64 hardware encoder cannot be loaded by an x64 emulated process. Compiling for ARM64 enables access to it. An emulated x64 process may still use software encoders if available.

I hope this helps resolve your concern. If you agree with my answer, please mark it as accepted.

Hi again Jay, that's very helpful. A couple more questions please, if you may:

1. So for an emulated program, what happens when it tries to use DXVA2 (or DXVA11)? Presumably it will not just fail as many existing video programs run under emulation OK. So it must be running a software video decoder instead - is this software decoder actully built into Prism (because the program will not necessarily have its own built-in software decoder)?
2. Re your comment on situation 2, DXVA2 might be available to the native ARM program if the driver supports DXVA2. Presumably this would be a standard driver provided by Qualcomm, so one might expect that either DXVA2 is likely to be available on (nearly) all Qualcomm "Windows on Arm" computers, or it is not available on all Windows on Arm computers. Do you know if there is any documentation that says whether the Qualcomm drivers actually do hardware acceleration of DXVA2 or just DXVA11?

Thank you for your response. Below are my current interpretations based on available Microsoft/Qualcomm info and observed runtime behavior.

1. Emulated DXVA2/DXVA11 Behavior: API calls proceed under x64 emulation but fall back to software decoding via Media Foundation's built-in decoders (e.g., for H.264/HEVC). Prism translates instructions but doesn't add codecs this matches how common players like VLC run without crashing.
2. DXVA2 vs. D3D11 on Native ARM64 (Qualcomm): Qualcomm Adreno drivers prioritize D3D11 video decode (ID3D11VideoDecoder/hardware MFT). I haven't found public Qualcomm or Microsoft docs explicitly confirming DXVA2 hardware acceleration on Snapdragon X, so I view it as unconfirmed (not "unsupported"). Recommend verifying via tools like DXVA Checker, IDirectXVideoDecoderService enumeration, or MF hardware MFT queries. Testing on-device is safest until authoritative sources emerge. No official Qualcomm doc lists DXVA2 HW support for Windows on ARM—practical validation advised.

• Qualcomm Developer Network - Adreno Video Codec SDK (focuses on MFT/D3D11 for ARM64).
• Qualcomm Blog - Latest Graphics Driver for Snapdragon X Elite (Nov 2024) (driver updates emphasizing modern video paths).

If you agree with my answer or find it useful, please consider marking it as accepted.