Last updated by Yermy Weiss on Apr 4

4K Video Signal Guide

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.

18 Comments

Hello I have a son a7S II and I would like to use the Odyssey 7Q+ recorder with my camera to record video in ProRes I saw an instagram saying get the most of your camera (picture had a Panasonic G5s an AJA HA5-4K and the Odyssey 7Q+ recorder) so I was curious why do I need AJA and not just using the Sony a7S II connected via Atomos HDMI that supports 4K at 60 fps, HD at 240 fps B&H # ATOM4K60C2 so why do I need and AJA between Sony and Odyssey 7Q+ recorder?

And how I connect them all together if AJA has quad link 3G-SDI so we have 4 3G-SDI outputs but Odyssey has just 2 3G-SDI inputs?

Or we can use just one 3G-SDI cable going out from AJA and connecting to Odyssey? (But as I understand 3G-SDI is not a 4K, 4K is 12G-SDI input?

Please let me know how it works? Thank you

Hello I have a son a7S II and I would like to use the Odyssey 7Q+ recorder with my camera to record video in ProRes I saw an instagram saying get the most of your camera (picture had a Panasonic G5s an AJA HA5-4K and the Odyssey 7Q+ recorder) so I was curious why do I need AJA and not just using the Sony a7S II connected via Atomos HDMI that supports 4K at 60 fps, HD at 240 fps B&H # ATOM4K60C2 so why do I need and AJA between Sony and Odyssey 7Q+ recorder?

And how I connect them all together if AJA has quad link 3G-SDI so we have 4 3G-SDI outputs but Odyssey has just 2 3G-SDI inputs?

Or we can use just one 3G-SDI cable going out from AJA and connecting to Odyssey? (But as I understand 3G-SDI is not a 4K, 4K is 12G-SDI input?

Please let me know how it works? Thank you

The Qdyssey 7Q+ Recorder is able to record UHD 4k through HDMI.  There is no need to use an SDI adapter to record with the A7SII, nor is there any benefit.  The A7SII is only able to output UHD at 30fps, that will not change with adapters.

Thanks!

We have a dual 3G SDI JVC monitor we use for color grading. I have a Blackmagic Decklink Pro video card that I have been using for years with Avid, Premiere and Davinci. In fact, you guys built the MAC pro with the card in it. I recently tried replacing the card with a New Blackmagic 4k
card and it did not support the dual 3G monitorin 1080p, even though they say it will. Since the monitor is 1080p the new 4K card does not down convert to 1080p. Since this monitor is a $4,000 monitor, I'm not about to get rid of it. I was on the phone with Blackmagic and they said the 4K card will not down convert to 1080p. Are they any other cards that will down convert 4K to 1080 dual 3G SDI--Thanks!
Bill

We have a dual 3G SDI JVC monitor we use for color grading. I have a Blackmagic Decklink Pro video card that I have been using for years with Avid, Premiere and Davinci. In fact, you guys built the MAC pro with the card in it. I recently tried replacing the card with a New Blackmagic 4k
card and it did not support the dual 3G monitorin 1080p, even though they say it will. Since the monitor is 1080p the new 4K card does not down convert to 1080p. Since this monitor is a $4,000 monitor, I'm not about to get rid of it. I was on the phone with Blackmagic and they said the 4K card will not down convert to 1080p. Are they any other cards that will down convert 4K to 1080 dual 3G SDI--Thanks!
Bill

We are not aware of a PCI Card that will down-convert a 4K Signal to an HD Signal through SDI.  You may need to look in to a product like the Blackmagic Design Teranex AV instead.  You can connect up to a 4k 12-SDI signal in to this unit and it will be able to down-convert it to HD and send out the signal as a Single 3G-SDI or even Dual Link HD-SDI.

https://bhpho.to/2E5YWTk

Thanks.

We are not aware of a PCI Card that will down-convert a 4K Signal to an HD Signal through SDI.  You may need to look in to a product like the Blackmagic Design Teranex AV instead.  You can connect up to a 4k 12-SDI signal in to this unit and it will be able to down-convert it to HD and send out the signal as a Single 3G-SDI or even Dual Link HD-SDI.

https://bhpho.to/2E5YWTk

Thanks.

Hi, I have an Atomos Shougun Flame and I would like to output 4K RAW 25p from it. My current SDI/BNC cable skips frames in that mode. What cable should I get?

You may want to look at cables that are specifically rated for 12G SDI, such as B&H Number CAL55CUHD006 from Canare.

https://bhpho.to/2yD0Ewn

So what is 2SI?  4k over 2 BNC cables 1080p interleaved ?

We are not quite sure of the question you are asking, feel free to email us at ask@bandh.com with more information, specifically what you are referring to by 2SI?

2SI is a method to encode the UHD raster into 4 video streams.  Quadrant square division is another.  The datarate depends on the frame rate, but typically a 2160p59.94 UHD video can be transmitted as 2SI over a single 12Gbps link or over 4x 3G cable links.  2160p59.94 Quadrant Square Division is only transmitted over 4x 3G links. 

Buyer beware when it comes to 2SI vs quadrants... Make sure your equipment uses compatible standards and frame rates.  Some products state they have UHD outputs, but in the fine print you see only at maximum frame rate of 30Hz, for example. 

Useful article, since it gives some authoritatve information abotu unofficial standards. It needs to be updated to include 12G-SDI, though. And Blackmagic now offers "Teranex mini" converters that can convert 12G-SDI to dual 3G-SDI or quad SDI.

The Panasonic GH4 claims to output 10-bit 4:2:2 4k video up to 30fps, over an HDMI 1.4 connection. This post claims that is impossible. Can you explain?

Hi Jon -

The Panasonic LUMIX GH$4 sends 4:2:2 8-bit or 4:2:2 10-bit video in real-time to external monitors or recorders via the micro HDMI output. An optional micro HDMI cable is required. When outputting a 4:2:2 10-bit signal over HDMI, video cannot be recorded on the SDHX/SDXC memory card in the camera.

Please contact us via e-mail if you have additional questions:  AskBH@BandH.com

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

Hi Vince -

We offer the recommended cabling in a variety of lengths:

Canare HD-SDI Video Coaxial Cable - BNC to BNC Connectors - 0.5'

Canare HD-SDI Video Coaxial Cable - BNC to BNC Connectors - 1'

Canare HD-SDI Video Coaxial Cable - BNC to BNC Connectors - 2'

We also offer this cable in longer lengths if you should require them.

Please contact us via e-mail if you have additional questions:  AskBH@BandH.com

Alternatively You may use Belden cable model 1505F  terminated with a Suitable HD BNC connector. 

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