The 4K First Mile: Launching 4K Streams

4K Connections and Cables

I love the HD-SDI connection standard that uses BNC-type connectors. It is a professional connection standard and is much more stable than the consumer HDMI standard. BNC signals are determined by the output device. When you split an SDI signal, none of the split signals rely on each other. HDMI, on the other hand, negotiates the signal resolution and frame rate between the output device and every connected device. It then selects the highest common standard between all devices.

This sounds great for consumers, but the negotiation process is a series of back-and-forth tests where all the connected devices go blank and intermittently connect until the common signal is determined. Not only does HDMI take longer to connect initially, it also takes longer to reconnect, and if you add or subtract a connected device, the interconnect negotiation process starts over again. This is not what you want when you are broadcasting a live video signal.

Unfortunately, the answer isn’t as easy as just using an HD-SDI connection for your 4K UHD signal from your video camera to your video switcher and webcast encoder. The HD-SDI standard required for a 4K UHD signal is 6G for 30P and 12G for 60P signals. Blackmagic Design is one of the few camera manufacturers to offer 6G and 12G HD-SDI video camera outputs (Figure 2, below), while most Japanese camera manufacturers (Sony, Panasonic, Canon, etc.) offer only 3G HD-SDI outputs, which are suitable for 1080 60P video signals.

Figure 2. Blackmagic Design's URSA line, unlike cameras from most other manufacturers, features 6G and 12G HD-SDI outputs, suitable for 1080p60 signals.

I’m a bit disappointed that 6G and 12G HD-SDI aren’t available on more video cameras, especially seeing that the 24G standard is already being developed by a SMPTE workgroup for 2160 120P support. As a result, most UHD 4K workflows are connected by the HDMI 1.4 (30P) and HDMI 2.0 (60P) standards. I should also note that the new HDMI 2.1 standard supports dynamic HDR and video resolutions up to 10K 120P.

The challenge in the typical 4K UHD workflow over HDMI is that, in addition to the interconnect issue I have already discussed, HDMI cables are limited to much shorter cable lengths for the same signal bandwidth as an HD-SDI signal. Most mid-range HDMI cables are also very thick, and this can cause strain or accidental disconnects on your camera’s HDMI port.

I recently came across HDMI cables from RedMere that allow for longer and thinner lengths. RedMere cables contain an integrated semiconductor chipset that draws its required power from the HDMI signal and boosts and equalizes the video signal. The result is a directional cable that requires less copper and is thinner and lighter. Although RedMere technology (first announced in 2008) isn’t new, until recently, RedMere HDMI cables were available only at a high premium from companies such as Monster. Now you can buy HDMI 2.0 cables with RedMere in 50' lengths for $29.99.

If you require a longer cable run than 50–60' over HDMI, then you will need to convert your HDMI signal to HD-SDI, CAT6, or fiber-optic cable. Some workflows will require you to convert the signal back to HDMI on the receiving end, while others will allow you to directly connect your fiber-optic or HD-SDI cable.

4K Video Switching

If you are mixing between two or more 4K UHD video or computer signals, you will need a hardware or software video switcher. With so many different resolution and frame rates to work with, the big thing to keep in mind is that if you need to up- or down-convert one or more of your video signals, you may need an external device to process this conversion.

Video conversion also can introduce unwanted delay in your video workflow. This delay becomes noticeable very quickly when you are also providing a live IMAG display and for these workflows. In general, hardware video switchers also have less processing delay than do software solutions such as vMix 4K or Wirecast. HDMI connections also introduce more delay into the signal-flow than do HD-SDI connections.

4K Capture Cards

Getting your 4K UHD video signal into your webcast encoder or software video switcher requires a 4K UHD video capture card. 4K capture cards are available for PCI Express desktop or workstation builds, but you may want to consider Thunderbolt or USB 3.0 models if also you want to use your video capture hardware on laptops. A good place to start your research for 4K capture cards (Figure 3, below) is vMix’s video capture hardware support page that lists the manufacturer’s model, number and type of input(s), and the connection requirement.

Figure 3. vMix recently certified the YUAN SC560 N4, a PCIe 4-input 4K HDMI capture card. 

4K capture cards don’t need to be expensive, either. A single-input Blackmagic Design DeckLink Mini Recorder 4K can accept either HDMI or 6G-SDI signals on a PCIe connection and costs only $195. If you have limited PCIe space and require multiple 4K inputs, you will want to look at the YUAN SC560 N4, a PCIe 4-input 4K HDMI capture card, that vMix recently certified.