Resolution Scaling for Hardware Encoders

[Xaymar]

Discussion Thread

https://github.com/Xaymar/obs-StreamFX/discussions/847

Provide a summary of the Improvement

Users should be able to choose a different stream and recording resolution without incurring the multi-copy overhead when a Hardware Encoder on the same GPU as OBS Studio is used. The ideal solution is a drop-in class that can be called from any current and future encoder.

Completion Requirements

• Easily integratable in future encoder implementations. A junior C/C++ developer should be able to integrate this change within 1 hour of starting.
  • This either means a separate class or direct integration into the common encoder factory.
• Code should have enough comments to be understood, but not too many.
  • int a = 1; // Assigns 1 to a is pointless.
  • a *= std::max(b/c, log(d)) / log2(e); should definitely have a comment.
  • Multiple comments may be grouped into one block preceding the difficult section.
• Code is licensed under GPLv2 or later.
• Support for NV12->NV12, I420->I420, I444->I444 and RGB->RGB.
• Scalers: Linear, Bicubic, Lanczos or Magic Kernel.
• Zero-Copy should stay functional, and scaling should have no to very little impact.
• Multi-GPU support should stay functional.
• Encoders can run at an integer fraction of the OBS Studio framerate without causing problems with OBS Studio's fixed function sequential pipeline.