Testing Dolby Vision with the Murideo 8k 7g through an extender

Testing Dolby Vision with the Murideo 8k 7g through an extender

Question - I can't get it to work properly with the Dolby Vision test patterns.  The TV does detect the right resolution and the DV flag, but the picture is all black.  It works fine if I connect the Seven directly to the TV without the extender.  SDR and HDR modes work fine through the extender.

If I use an Apple TV 4K instead of the Seven, it works fine through the extender in all modes including Dolby Vision.

The manufacturer of this extender thinks maybe the Seven is not compatible with CSC compression which they are using (as opposed to DSC).  Can you enlighten us about this, is it really some limitation of the generator?

Its because DOLBY VISION is not compatible with CSC compression (And hence not compatible with their extender). 

CSC modifies the Chroma sub-sampling to 4:2:0 from 4:4:4. 

How Dolby Vision works (Both methods and extender ramifications): 

Dolby Vision Sink-Led (RGB Tunneling Method) – The original HDMI signal is either 4:4:4 or RGB with 8BIT.  Using Dolby’s proprietary decoding methodology the Sink (Display) decodes the signal to 4:2:2 12 bit depending on frame rate.  In order for this to work on an extender it MUST NOT impart any influence on the chroma sub-sampling as that is where the deep color and VSIF (Vendor Specific Infoframe) reside.  This is the most accurate to the display method as the tone mapping is done by the display based of its own capabilities. 

Dolby Vision Source Led (AKA Low-Latency) – This is known as Low-Latency Source Led because the source itself preforms the tone mapping function based on EDID parameters.  In this case the source will send an HDMI signal that is 4:2:2 12 Bit.  With this signal, the VSIF  HDR Infoframe is also presented in real time on the HDMI link.  The ramifications on the CSC type extenders is you will still get a “Dolby Vision Pop” on the screen, but you will often see noticeable banding.  We like to point people to AVPro Edge because of this banding (They use a proprietary compression) – see this article https://www.avproedge.com/news/tech-tip-what-is-ict 

Extender capabilities based on technology: 

Generally speaking, copper extenders work on a 9Gbps PHY, this means that as the signal transverses that limit, compression becomes necessary.  Dolby vision is compatible with extenders taking into consideration the limitations. 

If it is a 9Gbps PHY (Like 99.99% of extenders) you can use:

  • Dolby Vision Sink-Led @ 1080P and 4K30
  • Dolby Vision Source Led up to 4K60 (Mind the banding) 

If it is a 16 Gbps PHY (Very new, very expensive) you can use:

  • Dolby Vision Sink-Led up to 4K60
  • Dolby Vision Source-Led up to 4K60 

I further recommend AVPro Edge because they manage the front end to where a source won’t excurse the capabilities of the product and they offer uncompressed options to cover all.  However, since Murideo is a professional generator, you can “force” the output as you need to test true infrastructure capabilities.

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