Complete Guide to Video Standards: SDI, HDMI, NDI, and SMPTE 2110
Ever-Evolving Video Technologies
There are more technologies to deliver your video content from your computer today than ever before, but unlike days of yore that had full words to describe these technologies, such as “Composite, Component, and S-Video”, today we are faced with an alphabet soup of acronyms and technical classifications. It is difficult to keep up with all of the changes that are taking place so this article is written to assist you with an understanding of these technologies.
Renewed Vision software products are designed to work in environments of all sizes, and to utilize all of these technologies (if not directly, through converters). There are pros and cons to each of them, so let’s dive in with an explanation of each of the technologies.
To start, be sure not to confuse the type of cabling with the type of video signal that is going over the cable. All of the video standards we are talking about in this article are digital, which means that it is less susceptible to the interference analog signals have historically been plagued with. The protocols used by each of these signal types are different and vary widely (resolutions, color space, color gamut, frame rates, etc.)
- Pros: inexpensive, readily available, built-in to your computer, uncompressed
- Cons: no locking connector, often finicky to work with, Copyright Protection (HDCP), short distance runs, doesn’t support alpha channel, not made for signal routers
HDMI is the default video signal standard these days and there likely isn’t a single video production of any size that doesn’t have some type of HDMI displays or devices. It’s ubiquity makes it somewhat inexpensive, and you’re far more likely to find cabling, displays, and other equipment with HDMI connectors at your local electronics store than any of the other standards. Every modern computer either has an HDMI connector built in, or support for HDMI via readily available adaptors.
HDMI has evolved as new and better standards have been adopted and now supports all HD and 4K resolutions, though you should make sure any cabling you purchase is made for newer video standards.
At its heart, however, HDMI was designed for consumer use and has some drawbacks. One serious drawback in production environments that are often filled with miles of cabling is that the HDMI connector type is not a locking connector, meaning that under just a bit of strain the cable is likely to pull out of its port. Further, as part of the standard, manufacturers are required to adhere to strict copyright protection (HDCP) in their devices that include HDMI. This copyright protection was originally intended to prevent the copying of video content since such digital copies would be identical to the original. By its very nature, signal converters are not HDCP compatible so if they are connected to a computer, DVD Player, or other consumer-centric device that wants an HDCP handshake, you may see or hear some unpredictable anomalies in your signal.
- Pros: Industry standard (SMPTE), longer runs for HD signals than HDMI, Locking BNC connectors, easily routable to multiple destinations, uncompressed
- Cons: More expensive for 4K, One-to-One routing
SDI, or Serial Digital Interface, is actually the oldest digital standard for the transmission of video signals and is the industry standard for broadcast video. There are few, if any, professional video cameras made today that don’t include an SDI output. SDI utilizes a coax cable, which is easily terminated (meaning it’s inexpensive and easy to make cables for) and can run longer distances than HDMI. The BNC connector type is a locking connector so you are less likely to have a signal unexpectedly pulled because someone stepped on a cable (fun fact: in stress testing, the cable breaks before the connector).
- Pros: inexpensive, readily available, uses standard network equipment, multicast signal, IP-network based (either hardwired or wireless)
- Cons: finicky on high network loads, compressed, uncommon in broadcast environments, very little hardware adoption
NDI, which stands for Network Device Interface, is a new, royalty-free system introduced by Newtek in 2015 for the distribution of video and audio streams over standard ethernet networks. Newtek, which has been in the video broadcast industry for over 35 years with products that have generally done things differently than the broadcast market at large, created this technology as an easy and inexpensive way for video to be multi-cast to multiple locations. Unlike SDI or HDMI connections which are point-to-point (meaning a dedicated connection of some sort has to be made between the source and destination with one video signal per cable)NDI is just digital data on a standard ethernet connection. It uses an auto-detect protocol so that any devices on the network can “see” available connections and “tune in” to receive them, as such there is no need for a specialized router like you would need for SDI or HDMI.
The great thing about NDI is also its achilles heal because, if not implemented properly, you can get a suboptimal experience. While NDI works over standard office switching equipment, it should not be assumed that you can use your current office network for the distribution of NDI feeds. A 1080i video feed, for example, is typically around 100 mbps so for optimal quality you should have a gigabit network with plenty of overhead to hold the various connections.
While it does not have the SMPTE acceptance of its peers, it has been widely adopted by software manufacturers as it is an easy-to-implement means of sending video signals between compatible computer and broadcast video equipment. Unfortunately, very little video hardware is presently made with support for NDI. Aside from Newtek itself which makes switchers and PTZ cameras, Panasonic is the only major manufacturer that has introduced support in its hardware products. There are some new companies that have sprung up with solutions specifically to convert NDI to/from SDI/HDMI, but until devices themselves include NDI support, its adoption will likely continue to be only for niche solutions (such as sending NDI from ProPresenter to PVP3 or live streaming software). NDI video is compressed, which means you’re not getting the highest possible quality signal, but the data rate is high enough that there are very few compression artifacts. Further, the latency is relatively low (meaning it is usable in live productions), and can be transmitted wirelessly on high-quality wireless networks.
Among the great features of NDI are its ability to transmit an alpha channel within its video stream so including transparency in the video signal is easy and doesn’t take separate video connections. In addition, because it works through standard ethernet protocols, it is easy and inexpensive to implement given that most computers feature built-in or easy ways to add ethernet ports. While you can transport various frame rates and resolutions over NDI, generally the receiver can receive multiple formats and automatically scale/transcode any input.
Unfortunately, NDI is still considered a “rogue” standard, meaning it hasn’t been ratified by the industry…we’ll go into this more later in this article. NDI is owned and maintained by Newtek, now owned by Vizrt, a leader in broadcast CG applications, but is freely licensable for use in software and hardware products.
- Pros: Future-proof, Fantastic routing capabilities, standard IP network based, stable performance, separated audio/video/meta-data signals
- Cons: Expensive, still evolving
Video standards are defined and ratified by SMPTE, the Society of Motion Picture and Television Engineers, which consists of industry professionals and manufacturers that work together to create standards so that equipment from various companies work with each other. Without this organization’s stamp of approval, you would likely have to purchase all of your equipment from a single manufacturer and innovation would stagnate.
A little under a decade ago, various manufactures embraced the vision of simply treating video/audio streams as packetized data on standard data networks. These manufacturers embraced different technologies and protocols which would have resulted in calamity without the ratification of some standard. To quote the organization, “SMPTE ST 2110 is a growing and comprehensive suite of standards enabling carriage, synchronization and alignment of audio, video and metadata over IP for professional media applications and applicable range of use cases, even to low latency applications such as live production, and capable of handling future resolutions, frame rates, color sampling and bit depths.” There is a lot in that sentence, but what it amounts to is that SMPTE 2110 is here now, but is evolving very quickly. The end objective is to be able to run the same network/fiber cabling to all equipment in a broadcast environment and for it to “just work”, whether for audio, video, comms, or ancillary data.
I use the term “standard IP network cabling” loosely here because when most people think of “standard network” we think about Cat6 cabling with RJ-45 connectors…the likes of which we see on most computer equipment. By and large, SMPTE 2110 does NOT utilize copper cabling as the bandwidth is just too small. Whereas you can get no more than 10Gbps on Cat6 cabling, SMPTE 2110 typically uses fiber with bandwidths of 10, 25, or 100 Gbps. The protocols are the same, but the bandwidth is far faster. As such, you won’t be able to output video streams in ProPresenter through your ethernet port anytime soon, but rather you’ll need video hardware similar to the SDI hardware we work with to transmit SMPTE 2110 feeds.
In practice, SMPTE 2110 should work in much the same way that NDI works… but unlike NDI, SMPTE 2110 is designed for uncompressed video and audio that is eminently reliable. As such, video and audio signals and switching equipment is hard-limited to the number of streams that any network connection will support. A 10gbps optical connection can support 6 HD feeds (each of which is 1.5Gbps uncompressed) for example.
In SMPTE 2110, all of the streams are independent…meaning the audio is not multiplexed with the video. All signals, or “essences” are timestamped so a device receiving a signal from a router can specify what video stream it received independently of what audio stream it receives independently of what closed caption feed it receives with confidence that all of the data will be synchronized. This makes it very different from SDI/HDMI which each carry a single set of video/audio/ancillary data from one point to another.
So, where does SMPTE 2110 stand at the time of this blog? Well, there is plenty of equipment available, but not all equipment is compatible with all things. For example, the 2110-20 implements embedded alpha in video streams for the first time… a great feature to be sure, but one that a lot of existing hardware isn’t capable of implementing. Further, while the protocols used by 2110 use network standards, the implementation is somewhat specialized for video, so common off the shelf routers won’t usually work with 2110…meaning more expensive hardware. There are two things that may accelerate this adoption. One is the 2110-22 standard which introduced compressed video quality which would make it more possible to use more standard copper-based switching equipment (the goal of manufacturers is to send a high-quality UHD/4K60 signal at 1Gbps). Beyond this, the technology will become more approachable as optical IP networking equipment becomes more affordable throughout the next decade.
Confused yet? We’re not done! Now there is IPMX (Internet Protocol Media Experience), introduced in 2020. Designed to enable carriage of compressed and uncompressed video, audio, and data over IP networks, the IPMX set of specifications and standards addresses the ProAV industry’s need for a single set of common, ubiquitous standards-based protocols that ensure interoperability for AV over IP. Right now, it’s just a codified set of SMPTE 2110 standards for the AV market, but this too will get more complicated.
All of the standards mentioned are digital…meaning it’s just data. The higher the resolution and framerates, the higher the data bandwidth required, and the shorter the distance your cables can run. For example, HDMI typically isn’t run further than 15 meters (49 feet). SDI rated for HD feeds can typically run 300 feet, but the same cable probably can’t carry a 4K feed more than 50 feet. Newer cabling technologies allow for 5up to 300 feet for 12G SDI feeds over coax, but it is more expensive, as one would expect.
All of the signal types described here can be made to go longer distances by using fiber optic converters. Further, all of them have embedded audio, which makes it far more convenient than what has historically been two separate cable paths for audio and video.
The Cleaner the Signal Flow, the Better
All of these signal types can be converted to the other signal types. As such, you needn’t worry too much about standardizing on a specific standard for fear that it will impinge on your ability to grow in the future. That said, the price of converters can add up, and each device that you add to your signal flow is another opportunity for failure. We’ve all seen and laughed at memes of audio or video connectors being contrived in multiple parts to adapt one connector to another…avoiding this step whenever possible in your original design of equipment will ensure fewer headaches later.
The drawbacks of each of the video standards shown are also their strengths, and vice versa. SDI and HDMI are mostly “it just works” protocols; meaning, so long as your equipment and cabling is rated for the resolution and frame rate you are using these will work. The benefit of NDI and SMPTE 2110 is that they ultimately are just data, which means that resolutions and frame rates and capabilities may change, but its unlikely that all of your equipment will need to be replaced as these changes happen because ultimately, the content is just packets of data on their respective networks. That said, when using IP based networking, the capabilities of the equipment you are using may not keep up with the evolving standards. No doubt most hardware will have firmware upgrades or provide backward compatibility for older devices, but gone is the somewhat mindless “it just works” of their predecessors.
|Infrastructure||HDMI Cabling||Coax Cabling||IP Network |
(10 Gigabit Minimum)
|Embedded Alpha||√||√ *|
|Embedded Audio||Up to 16 channels||16 channels||16 channels||Unlimited|
|Distance Limit with properly rated cabling||50 ft||350 ft||500 ft||Unlimited|
|Uncompressed Video||Uncompressed||Uncompressed||Compressed||Uncompressed & Compressed*|
* Recent updates include these features