2160p25 HLG Rec 2020 HDMI capture Ultrastudio Mini 4K

Hi there

I'm trying to capture the output of a source that is capable of both Rec 709 SDR and Rec 2020 HLG HDR via HDMI in 2160p25 on a Mac running Catalina and Desktop Video 12, Media Express 3.7. I'm using a Black Magic Ultrastudio Mini 4K. (I've previously captured Rec 2020 HLG 2160p50 with no problems from a different source)

Whilst in Media Express I can see valid video in the capture window for both Rec 709 SDR and Rec 2020 HLG HDR sources - but recordings in either Uncompressed YCbCr 10 bit or ProRes of the Rec 2020 HLG source are audio only, whilst when Rec 709 SDR is captured the video is present.

I'm using an HDMI splitter that allows EDID from my display to be used (and the splitter output indicates Rec 2020 and HLG when I'm playing back in that mode)

It's very weird that in Media Express I can see the video in the capture window, but not record it.

The only difference I can think of between the 2160p50 Rec 2020 HLG capture that was successful and the Rec 2020 HLG 2160p25 capture that wasn't is that the former was 4:2:2 or 4:2:0 YCbCr 10-bit via HDMI, the latter is RGB 8-bit (Yes - 8-bit HLG...)


Any thoughts?

OK - Capturing 10-bit Uncompressed RGB works - but YUV doesn't. Odd.