Video in Transition- Hauling a 4K load Over a 1080p Bridge

New technology brings new challenges and solutions in AV design

The transition from 3:4 analog to 16:9 digital HD was reasonably painless. For meeting rooms and living rooms, HD screens had had little impact on room design – they were about as tall as 3:4 screens, with more horizontal real estate.

Converting analog video to HD was a greater challenge for twisted-pair video distribution. “Video Voodoo” problems arose as the precise kind of wire twist affected distance, resolution and performance. Those problems faded away with the introduction of HDBaseT, a chipset that converted digital video into packets. Think of HDBaseT UTP cable as an 8G bridge, easily transporting 3G 1080p video, audio, control data and Ethernet for up to 300 feet.

Enter 4K, an easy step for TV vendors, not so easy for twisted-pair video. That 8G bridge now has to carry a 10-16G load, more with 4:4:4 color and 10-bit HDR. Not happening, so something has to change – lighten the load, strengthen the bridge, or a bit of both.

Building the Bridge with PAM

PAM stands for Pulse-Amplitude Modulation, that expresses data using amplitude in a series of signals. PAM-5, used by 1G Ethernet uses values of -2, -1,0,+1 and +2 VDC to represent bits of data. Each of the four twisted pairs carry up to 125 mbps, summing up to 1G of data. 10G Ethernet, both HDBaseT and IP Switching, employs PAM-16, encoding 16 levels with added physics. The limiting factor in PAM technology is RF noise, as it prevents the receiver from sensing the right levels. This is a key factor in 10G Ethernet, as the level steps are much smaller. For this reason, shielded cable should be used for all 10G applications. 2.5G/5G Ethernet uses a lighter version of PAM-16 designed for Cat 5e/6 UTP applications. Of course, optical fiber is always the best carrier, as there is no RF noise to interfere with the signal.

It’s interesting to note that AV platforms we view as different – AV over IP, QAM digital cable, 8-VSB off-air digital channels, and HDBaseT – are all based on variations of PAM technology.

Compression – Lightening the Load

Full 18G 4K60 HDR video can’t travel over a 10G bridge, so the stream has to be compressed to fit. There are two technologies in use today:

  • VESA Display Stream Compression (DSC) in newer HDBaseT systems, creates a visually lossless stream, typically at a 3:1 ratio, reducing an 18G 4K60 HDR stream to 6G with little loss in quality. Examples include Crestron DM 4KZ and WyreStorm 18G HDBaseT systems.
  • Motion JPEG 2000 was designed for video storage, reducing files by 3:1 without losing original quality. With today’s higher bandwidth, the codec has a new application in AV over IP technology:
    • 10G IP Switching. Employs 3:1 compression to deliver mathematically lossless video. In use today in SVDoE and Extron systems.
    • 1G IP Switching. Employs 20:1 compression to deliver visually lossless streams over 1G Ethernet networks. Available from Crestron, WyreStorm, Extron, Kramer and many others.

VESA DSC has a key advantage – compression only affects streams starting at 4K60 4:4:4, other streams are uncompressed.

The good news is there are solutions in place for the challenges in 4K video distribution.

  • Sites with existing Cat 5e/6 UTP wiring can transport 4K video using 1G IP switching gear, and companies like WyreStorm and others have HDBaseT extenders that can transport 4K video over Cat 6, with some resolution and distance limitations.
  • New installations have many options for 4K distribution over Cat 6a/7a STP cable or fiber.