4K Video Signal Guide

Last updated by Yermy Weiss on Apr 4

One of the most confounding aspects of 4K video production is the lack of accepted standards. And like many other parts of the emerging 4K workflow, 4K video signals are done in many different ways. The biggest problem is that there is still no broadcast standardized SMPTE 4K signal.

Without a supported professional method for distributing 4K most companies have had to improvise. Some use multiple existing HD video signals simultaneously and stitch them together, as is the case with Quad-Link HD-SDI. Other 4K products use existing consumer 4K standards, such as HDMI 1.4. One company even developed their own 4K signal.

The result is a widely fragmented group of 4K signals on the market. Getting these devices to work with one another will most likely require a converter box of some sort. To help navigate this confusing market this article discusses the various different signals that are used for 4K video, their maximum quality, and how to convert those signals to other signals.

Quad-Link HD-SDI

Quad-Link HD-SDI transmits 4K as four separate 2K or 1080p signals. HD-SDI is a SMPTE standardized signal for 2K and 1080p video distribution. This makes Quad-Link HD-SDI a reliable, though cumbersome, way to distribute 4K video. You will need four separate 75 ohm BNC coax cables that support at least 1.5 Gb/s of bandwidth for Quad-Link HD-SDI. Quad-Link HD-SDI supports both DCI 4K and UHD 4K. The maximum quality supported by Quad-Link HD-SDI is 10-bit 4:2:2 at 30p. HD-SDI is a proven and extremely reliable signal for HD video, which is probably why Quad-Link HD-SDI is the most common way of distributing 4K on professional broadcast equipment.

Quad-Link HD-SDI can be converted to the following signals:

  • HDMI 1.4 with either the Blackmagic Miniconverter SDI to HDMI 4K or the AJA Hi5-4K
  • Dual-Link 3G-SDI with the Blackmagic Multiplex 4K
  • 6G-SDI with the Blackmagic Multiplex 4K

Quad-Link 3G-SDI

Quad-Link 3G-SDI is very similar to Quad-Link HD-SDI but, as the name implies, uses four 3G-SDI signals instead of HD-SDI. The extra bandwidth of 3G-SDI allows Quad-Link 3G-SDI to transmit 10-bit 4:2:2 4K at double the frame rate (up to 60p) or to transmit up to 12-bit 4:4:4 at the same frame rate (up to 30p). You will need four separate 75 ohm BNC coax cables that support at least 3 Gb/s of bandwidth for Quad-Link 3G-SDI. Quad-Link 3G-SDI is the most useful for post production where the extra color information in a 4:4:4 signal can be utilized. Currently no 4K cameras output a 4:4:4 signal, but some capture cards do. Because Quad-Link 3G-SDI exceeds the bandwidth of all other 4K signals currently on the market there are no ways to convert a Quad-Link 3G-SDI signal into anything else. However any device capable of Quad-Link 3G-SDI should also do Quad-Link HD-SDI.

Dual-Link 3G-SDI

This is essentially the same signal as Quad-Link HD-SDI, but sent over Dual-Link 3G-SDI. The maximum quality available over Dual-Link 3G-SDI is 10-bit 4:2:2 4K at up to 30p. You will need two BNC cables that support 3 Gb/s of bandwidth for 3G-SDI. It is useful for reducing cable clutter since only two BNC cables are used. Dual-Link 3G-SDI is not currently output by any 4K cameras but converter boxes exist to convert it to and from other 4K formats. Also some capture cards can output Dual-Link 3G-SDI and some monitors will input Dual-Link 3G-SDI.

Dual-Link 3G-SDI can be converted to the following signals:

  • HDMI 1.4 with the Blackmagic MiniConverter SDI to HDMI or AJA Hi5-4K
  • Quad-Link HD-SDI with the Blackmagic Multiplex 4K
  • 6G-SDI with the Blackmagic Multiplex 4K

6G-SDI from Blackmagic

Blackmagic Design seemingly got tired of waiting for SMPTE to finalize a 4K signal and went ahead and released their own. Blackmagic Design calls their 4K signal 6G-SDI, but it is important to note that 6G-SDI is not a standard.  When or if SMPTE standardizes a 4K signal they may or may not decide to call it 6G-SDI. And there is chance whatever SMPTE 6G-SDI ends up being it will not be compatible with Blackmagic's iteration of it.

With that disclaimer out of the way it’s time to move on to the good news. 6G-SDI uses just one BNC cable to send 10 Bit 4:2:2 4K at 30p or 24p. You will need one BNC cable that supports 6 Gb/s of bandwidth for 6G-SDI. Finding a compatible cable can be tough because cables are not advertised as supporting 6G-SDI since it’s not a standard. Blackmagic says most high-quality 3G-SDI cables should work over short distances. But as of yet we haven't been able to test this. Currently only Blackmagic products utilize this signal, but Blackmagic Design has announced a number of converter boxes to convert most other 4K signals to and from 6G-SDI.

6G-SDI can be converted to the following signals:

  • HDMI 1.4 with the Blackmagic MiniConverter SDI to HDMI 4K
  • Dual-Link 3G-SDI with the Blackmagic Multiplex 4K
  • Quad-Link HD-SDI with the Blackmagic Multiplex 4K      

Quad-Link HDMI 1.3

Quad-Link HDMI 1.3 transmits 4K as four separate 1080p signals. It only supports UHD 4K and is currently only supported by JVC. You will need four separate HDMI 1.3 cables to distribute Quad-Link HDMI 1.3. In theory, Quad-Link HDMI 1.3 supports 10-bit 4:2:2 UHD 4K at up to 60p, but the only product that outputs Quad-Link HDMI is the JVC HMQ10 which outputs an 8-bit 4:2:2 signal at 60p. No converter boxes exist to convert Quad-Link HDMI 1.3 to or from any other 4K signals. You could attempt to use four separate HDMI to HD-SDI converters, but because HDMI lacks any sort of genlock the signals could end up being out of sync.

HDMI 1.4

HDMI 1.4 is used on pretty much all UHD television sets and is the closest thing to a consumer standard for 4K signals available right now. The main limitation of HDMI 1.4 is bandwidth, as HDMI 1.4 is only able to handle 8-bit color at 24p or 30p. This is suitable for most situations, but 8-bit color is limiting for proper color correction. Also, HDMI is notoriously finicky when being used with switchers, distribution amplifiers, or any other similar types of devices. For this reason there are no converter boxes that convert HDMI 1.4 to other signals. But there are a large amount of conversion boxes available to convert other 4K signals into HDMI 1.4.

These signals can be converted into HDMI 1.4:

  • Quad-Link HD-SDI with the Blackmagic MiniConverter SDI to HDMI 4K or the AJA Hi5-4K
  • Dual-Link 3G-SDI with the Blackmagic MiniConverter SDI to HDMI 4K or the AJA Hi5-4K
  • 6G-SDI with the Blackmagic MiniConverter SDI to HDMI 4K          

HDMI 2.0

HDMI 2.0 is the forthcoming HDMI standard. It supports up to 18 Gb/s of bandwidth and allows for higher frame rates and bit depths than HDMI 1.4. HDMI 2.0 supports 12-bit color at up to a 60p. It is also backwards compatible with HDMI 1.4 cables. HDMI 2.0 UHD TV sets aren't on the market yet, but some current HDMI 1.4 UHD sets should receive a firmware update to support HDMI 2.0. Like HDMI 1.4, HDMI 2.0 will most likely be hard to use with switchers and other forms of signal distribution, but could be a good option for post equipment since it supports a higher bandwidth than even Quad-Link 3G-SDI.

There are no converter boxes that work with HDMI 2.0 yet, but since TV sets will be able to update from 1.4 to 2.0 via a firmware update you might see some current converter boxes being upgraded to HDMI 2.0 in the future.

Mini Converter SDI Multiplex 4K from Blackmagic Design

The Mini Converter SDI Multiplex 4K is a very useful mini converter from Blackmagic. It can convert between almost any BNC-based 4K signal. It supports Quad-Link HD-SDI, Dual-Link 3G-SDI, and Single-Link 6G-SDI. It is very useful for converting between various 4K signals, or for working with any Blackmagic design 4K equipment that supports 6G-SDI. It can be powered with AC power or by battery with an optional adapter.

Mini Converter SDI to HDMI 4K from Blackmagic Design

The Mini Converter SDI to HDMI 4K is a mini converter from Blackmagic that converts Quad-Link HD-SDI, Dual-Link 3G-SDI, and 6G-SDI to HDMI 1.4. It is a great converter for using low cost UHD TV's for 4K viewing. It is also a great option if you are working with the Blackmagic 4K Cinema Camera. It is AC powered but can also be powered by battery with an optional adapter.

AJA Hi5-4K (AJA)

The AJA Hi5-4K is a mini converter from AJA that converts both Quad-Link HD-SDI and Dual-Link 3G-SDI to HDMI 1.4. It is ideal for using low cost UHD TV's for 4K viewing. It supports both DCI 4K and UHD 4K and is able to crop or scale DCI 4K signals for viewing on UHD TV sets that don't support DCI 4K. It is AC powered but can also be powered by battery with an optional adapter.

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Hi ! What kind of bnc wire should I use for outputing a 4k signal out of my sony fs700 to an odyssey 7q ?

Any ideas ?

Thanks