HDMI, The ALMOST Universal Audio/Visual Standard

By Erick Engelke and Mark Bruvelaitis
Updated October 3, 2025

There is no single universal Audio/Visual standard, but in 2025, HDMI comes close by being supported either directly or through conversion adaptors from EGA, VGA, DisplayPort, composite, S-Video, DVI and others with five different possible connectors. It is a licensed standard with all the benefits and challenges to be expected with independent vendor implementations over the last 22 years.

There are several HDMI standard specifications (see link). First introduced in 2003, HDMI has gone through a number of versions, each version adding new features while maintaining backward compatibility.

By 2021, about 10, billion HDMI-enable devices have been sold worldwide. As with many interoperatble multi-vendor systems, testing for compliance was immediately recognized as challenging and important, and the first Authorized Testing Centre (ATC) was opened in 2003. By 2013, there were over 1,300 different HDMI adopters.

For our classroom teaching systems, we have focused on HDMI 1.0. With its maximum clock rate of 165 Mhz, it can support 1080p and WUXGA (1920x1200) at 60 Hz. In theory, every HDMI-compliant system should be backward compatible with the 1.0 base version. In reality, there are occasional rare exceptions to that rule.

There are various issues which can sometimes make HDMI fail:

Internally, HDMI uses TMDS (Transition-minimized Differential Signalling) to serially transmit high speed data and offer robust clock recovery as well as electromagnetic interference reduction, as well as supporting both longer cables and inexpensive short ones.

Our equipment (and IST’s) is all tested and verified to be compliant with HDMI 1.0, the baseline standard. All HDMI compliant products negotiate a handshake between the source (eg. computer) and the sink (eg. projector) and should throttle back to the maximum compatible standard – which would be 1.0 in this case and exchange data such as the highest quality shared features including resolution and refresh rates.

This exchange shares their EDID (Extended Display Identification Data) and HDCP (copyright projection) compliance before any data is shared. So often compatibility failures due to HDCP are immediate upon connection due to the failed exchange. HDCP non-compliance often results in connected displays intermittently cutting to a black or green screen or not working at all. On the Crestron touch panel within the "laptop" page we provide the option to toggle HDCP compliance on/off at the HDMI input. This can often remedy the symptoms of HDCP non-compliance but is not a reliable "fix" as this is dependant upon the device’s implementation of the specification.

The distances within our teaching spaces between the podium and the projects require the HDMI specification to be converted to allow for the long cable lengths. Crestron Digital Media Video Switchers consisting of modular input and output cards along with external transmitters and receivers distribute the HDMI audio and video signal across a standard STP cable. This increases the maximum distance of the signal from 15m to 100m with no loss in signal strength or quality. These switchers also allow for remote video switching via the touch panel and distribution of the signal across multiple displays and projectors.

Furthermore, problems can exist at the driver level or the client operating system or the system firmware.

When something doesn’t work as expected, clearly either the classroom system is at fault or there is something about the configuration of the computer device or its cable connector. All three must be tested. This unfortunately takes time and is challenging if there is already a class in session.

One may wonder how we test and verify that the sink device is indeed working and meeting the specifications. Obviously in a Bring Your Own Device (BYOD) system, it’s impossible to guarantee success with every possible configuration in the market. Interoperability in any standards environment is challenging, and it’s accomplished with known reference implementations against which we can test.

We certainly do test with a typical laptop, but we also have an industry-standards compliant device which generates known test patterns. We and IST’s ITMS use the AVlink HDMI Pattern Generator PG-N1.

The pattern generator has the benefit of being guaranteed to generate known patterns, at known resolutions and frequencies, at known HDMI specifications. It is calibrated and expected to be more reliable than a consumer-grade device such as a laptop.

If the sink system checks out, our natural inclination is to suspect the client device has an issue. Our systems can display the EDID and HDCP values negotiated by the source device, and we use that information to make an informed initial support decision.

All computer based systems, including classroom technologies, may have rare periodic issues and require the occasional reboot following extended periods of successful operation.

We try to keep note of how often subcomponents require a reboot or other nudging. If it changes from rare to more frequent, the component will usually be replaced.

Sometimes users attempt to use extended wireless technologies such as Microsoft Miracast, Apple’s AirPlay or Google’s Chromecast. All of these are consumer friendly technologies which are great at home but simply do not work in the enterprise environment. Most assume a shared broadcast medium (eg. home Wifi), but the campus Wifi is not compatible by design since it is designed and configured for security first and foremost.

There are commercial technologies which are compatible and give similar functionality, but they are much more expensive to purchase, and thus are rarely deployed in the field.