Question about the 'color sampling' options in x265 base Main 10 settings

[Selur]

Does Hybrid treat the video source as 4:2:0 (instead of proper conversion from 4:2:2 to 4:2:0) whenever Main 10 is used, regardless of the actual source chroma sampling, or does it do proper 4:2:2->4:2:0 ?

In the x265 settings you specify the color sampling of for the encoder.
If your source is for example 4:2:2 and you tell Hybrid to use x265 with 4:2:0 it will do a 4:2:2->4:2:0 conversion during the decoding/filtering of the source.
Same goes if your source if 4:2:0 and you tell Hybrid to encode to 4:4:4, Hybrid will convert the 4:2:0 input to 4:4:4 before feeding the encoder.
Some goes for the color precision. If your input is 4:2:0 8bit and your tell Hybrid to use an encoder with 4:2:2 10bit, it will convert to that output format during the decoding/filtering of the source.
Hybrid tries to avoid having encoders do other stuff than encoding.

Hope this clears things up for you.

Cu Selur