Dolby Vision HDR recording on iPhone 12 series

@bford and other AVFoundation Engineers, can you please respond to this? How is Clips app by Apple recording in 10 bit Dolby Vision HDR format?

I see 4 new types of AVCaptureDeviceFormats with codecType 'x420'. Does x420 stands for extended 10 bit buffers?

Code Block 
---Format <AVCaptureDeviceFormat: 0x283b9c520 'vide'/'x420' 3840x2160, { 1- 30 fps}, HRSI:4224x2376, fov:70.291, supports vis, max zoom:129.12 (upscales @1.00), AF System:2, ISO:33.0-3168.0, SS:0.000014-1.000000, supports wide color, supports multicam>, AVMediaType(_rawValue: vide), <CMVideoFormatDescription 0x28375a190 [0x1f5b24660]> {
	mediaType:'vide' 
	mediaSubType:'x420' 
	mediaSpecific: {
		codecType: 'x420'		dimensions: 3840 x 2160 
	} 
	extensions: {(null)}
}