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Old 21st January 2019, 07:50   #54369  |  Link
Asmodian
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Join Date: Feb 2002
Location: San Jose, California
Posts: 4,406
DXVA2 Copy-back copies the video data from the memory on the GPU to system memory after hardware decoding. This allows code that runs on the CPU to access the video data but takes PCIe bandwidth. The data is also copied back to the GPU for further processing by madVR, and then finally sent to the GPU driver for display. This is why you want at least PCIe 2.0 x16 or PCIe 3.0 x8. For 4K60 HDR you might need more?

To complicate this Nvidia, with all drivers as far as I know, has that odd half pixel chroma offset which madVR avoids in copy-back mode by handling all chroma scaling itself. With DXVA2 Native there is a blur or similar damage when coping the chroma to madVR (GPU to GPU memory copy), even when using non-dxva chroma scaling. D3D11 Native avoids this issue. Nvidia's DXVA2 deinterlacing still has chroma issues no matter what chroma scaling you use.

Everything seems to work well for me with the current 417.71 drivers on a RTX 2080 Ti, Win10 1809 17763.253. HDR requires 10-bit output but both D3D11 fullscreen windowed and exclusive work well, with the GPU outputting 8-bit RGB to my LG C7P. I can add a custom mode for 23.976 Hz and optimize it.
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madVR options explained

Last edited by Asmodian; 21st January 2019 at 08:02.
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