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Comment by jorvi | Hacker News Reader

Why would it be a better option than VAAPI?

Decoding h264/h265 in fixed (CPU) hardware is much more efficient than on the GPU.

Don’t get me wrong, its still miles and miles better than software decode.

VAAPI is also using the GPU. The fixed-function video decoders are on the GPUs, not the CPU. That just happens to be using the iGPU on Intel so you don't need a discreet GPU necessarily, but this is also missing if you have a CPU-only sku like the -f suffix parts

The only difference is the vulkan spec is _in theory_ cross-platform. However, since MacOS doesn't support Vulkan and MoltenVK doesn't implement this extension (and probably won't), and this extension also isn't implemented on Android, then your scope of actual availability is quite pathetic. So it probably doesn't make sense to move off of VAAPI regardless unless you really want Linux & Windows to share a codepath, even though you have something OS-specific anyways for MacOS/iOS & Android.

It's unhelpful to bundle this into the "GPU" at large and is only true for desktop systems anyway. On mobile, video decoding, GPU and display pipeline are typically different hardware blocks often made by different companies.

> MoltenVK doesn't implement this extension (and probably won't)

Since Khronos appears to have decided to require manual DPB management, this cannot be implemented in HW on macOS by MoltenVK.

Huh, I stand corrected. I always figured they stuffed it in its own little bit of silicon. Thanks for clearing it up!

Intel does do this, they call it Quick Sync Video. There's support for it in vaapi. AV1 is only if you have a Gen12 iGPU or newer, or Arc.

I might just be bad at Google-fu, but my understanding is that -F processors don’t have Quick Sync, which seems to imply that the iGPU is required in some capacity.

Vulkan Video Extensions use the same physical hardware as VAAPI, but with a little bit less of forcing you to do codec-specific nonsense. It should be better in that it's much easier to get a zero-copy Vulkan texture from the decoded frame.

The GPU has also the fixed function video encode like integrated CPUs. Both VAAPI and Vulkan Video address the same hardware. Differences are in the API itself (with Vulkan being more explicit) and potentially in which vendors (or OSS driver developers) support which API in what degree.

Do CPUs have fixed video decoders? I thought those were only included in GPUs, including iGPUs.

Yes, every Intel consumer CPU has included a hardware video block since Haswell, called Quick Sync Video.

That block is a part of the included iGPU though.

Intel CPUs without iGPU, like the F-series, do not support QSV.

I think not being tied to VAAPI reduces the chain of development (like you don't need to wait for Intel to add something first since they are the primary developers of VAAPI in general).

Could anyone elaborate on the difference between software decoding and CPU decoding? Software decoding uses the CPU right?

That's right. "Software decoding" means the decoding algorithms run on the CPU. (As opposed to "hardware decoding" which typically means the work is done by some fixed-function video units on e.g. a GPU)

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