The shaders implement chroma upscaling based on the closed least squares solution for linear regression, inspired by the adoption of the same technique in modern video codecs. Since a simple linear regression obviously doesn't take into account pixel distance, the prediction is mixed with the output of a normal resampling filter based on how high the correlation between luma and chroma is.
You can control which local linear regressions you want to use with USE_12_TAP_REGRESSION, USE_8_TAP_REGRESSIONS.
The lite variant offers better performance at the expense of some quality.
The shaders are experimental and minor improvements are being made over time. If you have any suggestions, feel free to send them.
Add something like this to your mpv config:
glsl-shader="path/to/shader/CfL_Prediction.glsl"