Strato is a high-performance source device, capable of playing 4K Ultra HD content encoded at data rates of 100 megabits per second (Mbps) or higher. It supports 10-bit color, and high dynamic range (HDR) content. Taking full advantage of Strato’s capabilities requires careful attention to HDMI connections, cabling, and configuration. This page describes how HD video standards have evolved to Ultra HD, and what issues to watch out for in a Strato 4K installation.
Moving from HD video to Ultra HD video
Ultra HD video brings with it several new concepts and HDMI video standards, and, unless your equipment and cables meticulously comply with these standards, you may have interoperability issues. In the past, DVDs and Blu-ray discs established HDMI video standards that most equipment adopted over time. Most common is the HD video format 1080p, which uses a resolution of 1080 lines of pixels and a frame rate of 24 or 60 frames per second (fps). HD movies are copy protected with HDCP, which has a version number like 1.x. Finally, the color standard popularized by Blu-ray discs is called Rec. 709 or BT.709, and these colors are delivered with a bit depth of 8 bits per channel and a luma mapping that uses an exponential “gamma” curve (also called an electro-optical transfer function, EOTF).
As the HDMI standard has evolved over time, its bandwidth capabilities have increased to keep up with higher resolutions and denser color spaces. HDMI 1.0 maxed out at a video bandwidth of 3.96 Gbps, and even as recently as HDMI 1.4, introduced in 2009, bandwidth was limited to 10.2 Gbps. While it’s true that HDMI 1.4 was the first version of HDMI to support Ultra HD resolutions, its bandwidth isn’t sufficient to support many of the features of today’s higher-bandwidth 4K sources.
For Ultra HD (UHD) video from sources like Strato, in both standard dynamic range (SDR) and high dynamic range (HDR), every aspect of the older standards can change:
- HDMI version:
- 2.0 or 2.0a (HDR) or higher
- 4K, also called 2160p, with twice the lines of HD video.
- Copy protection:
- Color for Standard Dynamic Range (SDR):
- Color for High Dynamic Range (HDR):
- BT.2020, sometimes called Wide Color Gamut (WCG), a larger color space than BT.709.
- An EOTF function called PQ or ST.2084, which allows for higher contrast than gamma without banding.
- Bit depth:
- 10 or more bits per channel. Greater bit depth reduces the chance of banding in smooth color gradients, particularly for HDR content.
- Signal bandwidth (chroma subsampling refers to how color is allocated per pixel, 4:4:4 being the most color information and 4:2:0 being the least):
- 10.2 Gbps or less, for
- 2160p24, a common native format for movies
- 2160p60 with 4:2:0 chroma subsampling (8 bits per channel)
- 13.5 Gbps, for
- 2160p60 with 4:2:0 chroma subsampling (10 bits per channel)
- 18 Gbps, for
- 2160p60 with 4:4:4 chroma subsampling (8 bits per channel)
- 2160p60 with 4:2:2 chroma subsampling (10 bits per channel)
Types of 4K Displays
Achieving Strato’s highest video output quality requires a 4K HDR display capable of receiving and displaying an 18 Gbps HDMI 2.0a signal with HDCP 2.2.
As well, if Strato is connected to the display via intermediate devices (such as an audio processor, an A/V matrix switch, an active HDMI cable, or an HDMI extender), every device in that chain must support the required HDMI and HDCP versions to display 4K HDR at full fidelity.
Early 4K Displays
The earliest 4K displays lack the HDCP and HDMI standards now required to play 4K Ultra HD movies. other older displays may be able to display some 4K Ultra HD signals but without the latest features, like HDR.
Support for HDCP 2.2
HDCP 2.2 copy protection is required to play 4K Ultra HD and 4K HDR content with Strato. Some early 4K display devices do not support HDCP 2.2 and will not be able to display 4K Ultra HD content when used with Strato. Consult with the display’s manufacturer to see if an upgrade is available. If a display does not support HDCP 2.2 copy protection, but does support HDCP 1.x, Strato will down-scale the 4K Ultra HD content and output it at up to 1080p resolution. 4K HDR content cannot be down-scaled.
Support for HDMI 2.0 and HDMI2.0a (HDR)
Strato also requires HDMI 2.0 to properly display 4K Ultra HD content (2.0a for HDR content). One might expect that a display that supports HDCP 2.2 is also an HDMI 2.0 display, and vice-versa. Unfortunately, the situation is more complicated. Some early HDMI 2.0 displays do not support HDCP 2.2.
Support for lower-bandwidth HDMI signals
Some HDMI 2.0 displays only support data transfer at 10.2 Gbps, rather than the maximum 18 Gbps included in the HDMI 2.0 specification. The lower speed places some limits on how Strato displays 4K Ultra HD and 4K HDR content. Note that some equipment describes HDMI bandwidth in terms of frequency rather than data rate. A 10.2 Gbps connection or cable may also be called 340 MHz, and an 18 Gbps connection may also be called 600 MHz. In Strato’s Browser Interface, video can be configured to a lower bandwidth: see the Support page entitled HDMI Troubleshooting for Strato