There is no HDR on the Mac because MPV is currently using the OpenGL interface for rendering video. Apple’s insistence on creating their own graphics API (Metal) and refusal to adopt a cross-platform one (Vulkan) is why it doesn’t use a more modern interface. There is some on-going work to address this by the open source community by creating a layer that implements Vulkan on Metal (which is really a job Apple should’ve done). That work could bring HDR to the Mac.
As per metadata passthrough, I’ve not looked at the APIs for Metal in depth but my gut tells me that there is no way to accomplish metadata passthrough because that would be consistent with Apple’s style.
