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HDMI Best Practices for Strato

To achieve the best possible audio and video performance in a given installation, you may need to use both of Strato’s HDMI outputs, or adjust some of Strato’s settings.  The approach you take will depend upon the capabilities of the display and any intermediate devices like AV receivers. Consult the Kaleidescape Support page entitled Strato and Ultra HD Video Standards for context.

Best Quality, Single Connection

To achieve maximum image quality, Strato must be connected to a display that supports HDMI 2.0a at 18 Gbps with HDCP 2.2.  The HDMI cables must also be certified to support these standards. If the signal is routed through an audio receiver, the receiver must also support both HDMI 2.0a at 18 Gbps and HDCP 2.2.  Such an installation allows for maximum video quality at all 4K Ultra HD frame rates, and fully supports 4K HDR at up to 60 frames per second.
In Strato’s Browser Interface, the default video configuration “Avoid Display Mode Changes” plays:
  • The on-screen display (OSD) at 2160p60 4:2:2 with 8 bits per channel;
  • SDR 4K movies at 2160p60 4:2:2 with 10 bits per channel, BT.709 color space;
  • HDR 4K movies at 2160p60 4:2:2 with 10 bits per channel, PQ EOTF and BT.2020 color space.
While there would be a change in EOTF and color space for HDR, sometimes shown with an icon on the TV as “HDR Mode”, there is no video mode change and so the transition between the OSD and the movie should be fairly seamless.

Playing movies in their native format

In some cases, a customer may be more interested in the best possible video fidelity than in seamless transitions between the OSD and the movie, and so, in Strato’s Browser Interface, the video configuration “Allow Display Mode Changes” plays:
  • The OSD at 2160p60 4:4:4 with 8 bits per channel (SDR);
  • SDR 4K movies at 2160p24 4:4:4 with 10 bits per channel, gamma and BT.709 color space;
  • HDR 4K movies at 2160p24 4:4:4 with 10 bits per channel, PQ EOTF and BT.2020 color space.
This configuration plays movies in their native format, and also displays the crispest-looking graphics for the OSD; however, the video mode change may cause a delay or momentary flash at the start of movie playback. (Note that in the UK and other countries using the PAL format, content is displayed at 25 or 50 frames per second rather than 24 or 60.)

Playing movies on 1080p displays           

Strato provides a great experience with a 1080p display.  4K Ultra HD content is down-scaled for display at 1080p, and the Kaleidescape onscreen display runs at a full 60 fps.  Using Strato with a 1080p display is a good choice in an installation that has a mix of 4K and 1080p displays, especially if the 1080p displays may be upgraded over time.  If you can use 18 Gbps-capable cables, a later upgrade should also go more smoothly. Note that while 4K Ultra HD content can be down-scaled, 4K HDR content cannot. This is because 1080p displays don’t support HDR, and Strato cannot convert HDR content for playback on non-HDR displays.

Best Quality, Dual Connection

A common situation is one in which the display supports HDMI 2.0 or 2.0a at 18 Gbps with HDCP 2.2, but the AV receiver either does not support HDMI 2.0 and HDCP 2.2, or supports HDMI 2.0 at only 10.2 Gbps.  You can still achieve maximum video (and audio) quality in such a system by using the second (audio-only) HDMI port on Strato. Connect the display directly to Strato’s primary (VIDEO) HDMI port, and connect the receiver or audio processor to the secondary (DIGITAL AUDIO) HDMI port.  This dual connection allows the full video capability of Strato to be delivered to the display, while still providing full fidelity audio such as Dolby Atmos to the receiver.

Very Good Quality, Single and Dual Connections

If the display supports HDMI 2.0 and HDCP 2.2, but at 10.2 Gbps, Strato can still output 4K Ultra HD, including 4K Ultra HD at 60 frames per second.  However, at 60fps, video will be limited to 8-bit color, which can produce color banding with some content. With such a display, configuring Strato to “Allow Display Mode Changes” in the Video tab of the browser interface’s Settings dialog will allow Strato to switch to 24 frames per second for movies.  At 24 fps, Strato can output 10-bit color and HDR content even over a 10.2 Gbps link for displays that support it, so the image is identical to what you would see on an 18 Gbps connection. As with the 18 Gbps connection options described above, you can connect the audio equipment to the second HDMI port to if the audio equipment has HDMI or HDCP limitations that the display does not. Even if the display only supports a maximum of 10.2 Gbps, consider choosing cables that are tested to work at 18 Gbps or higher, especially when cables are run in-wall or in other difficult to replace installations.  This will help to ensure a smoother upgrade path to a new display in the future.

HDMI Cables

One of the most common sources of interoperability issues is poor-quality or overly-long HDMI cables. Cables that work well for 10.2 Gbps signals may not work at all for 4K 18 Gbps signals, showing either no video signal, flashing, or snow. For runs carrying an 18 Gbps signal up to 15 feet, passive cables should meet these criteria:
  • HDMI High-Speed cable tested to at least 20 Gbps;
  • Double Shielded;
  • AWG number for the conductors of 26, 24, 22, or lower.

Examples of such cables include those carrying a Premium HDMI Cable Certification, and cables that have been given a  4K-18G-DC certification by DPL Labs.

For runs longer than 15 feet, it may be necessary to use an active cable (including fiber optic cables) or an extender system. However, in our testing, many active cables and extenders have been unable to reliably support 18 Gbps signals in all situations, despite how they are labeled. The following document contains our specific recommendations for cables longer than 15 feet, based on testing performed in our engineering labs: Kaleidescape Recommended HDMI Cables.


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