[larsete]

Hi Jogal. Thanks for all the good work on this fork.

I may have found a/the cause of the stuttering/tearing that some NVIDIA owners are still experiencing. I use an Intel 6i3 with a GTX1650 4gb GPU running 441.66 drivers. 

I have tried all of your releases as they were posted.  Almost all work fine except for persistent stuttering when playing 4k HDR 23.9fps content. I have tried many Kodi and NVCPL settings, including power management modes and vsync modes - nothing was 100% successful. Verbose debug logs never showed anything unusual. Dropped/skipped frames were zero or very low and static. Setting "Maximum Performance" power mode in NVCPL reduced it, but did not eliminate it. However, MPC-HC/MadVR works perfectly.

The stutter shows up as the lower portion of the presenting frame being overwritten by a future frame (ie from 3 frames later on), but then the next presented frame is back in correct sequence. Very apparent on slow panning scenes. It shows up as a weird "jump forward-jump back" stutter/tearing - not like vsync tearing where the (torn) frames stay in correct sequence. It looks like the front buffer is being overwritten prematurely (not just swapped out) by the renderer before its been released.

I cloned your 1.9.1 git and found the following code in DeviceResources.cpp near the exit point of the DX:eviceResources::ResizeBuffers function:

          // Ensure that DXGI does not queue more than one frame at a time. This both reduces latency and
          // ensures that the application will only render after each VSync, minimizing power consumption.
          ComPtr<IDXGIDevice1> dxgiDevice;
          hr = m_d3dDevice.As(&dxgiDevice); CHECK_ERR();
          dxgiDevice->SetMaximumFrameLatency(1);
      }

This sets the number of frames that can be queued for presentation to 1. The Microsoft DXGI guidance says that this should be set to a value >3 for video playback workload.  Value of 1 is used for gaming where you want lowest latency and can tolerate some tearing to achieve fast user input response onscreen. Max value allowed is 16.

I set this value to 8 (taking a hint from default MadVR settings). I also moved this code snippet below the ELSE block it was in, so it executes every time ResizeBuffers is exiting (to be sure, to be sure). The stuttering/tearing has now disappeared entirely. 4k HDR 23.9 fps plays very smoothly. To push the point, I set NVCPL power mode to "Optimal power", vsync to "Use Application Setting", and also set 12 bpc colour in the "Change Resolution" menu. Kodi settings are "Adjust refresh rate" always, "Sync Playback" off, true fullscreen. No more stuttering or tearing - and according to GPU-Z, the GPU loafs along at a GPU clock of 360mhz (down from 1890) and a memory clock of 405mhz (down from 2000).

Perhaps this change should really be considered in the master branch, but the stuttering problem only manifests (for me) when running the heavier 4k HDR workload on the GPU with Windows DXGI. Others might be getting stuttering on non-HDR workloads that push their GPUs a bit.

Cheers from Oz.

Great research there! Thank you from one nVidia user suffering from it