HDMI offers the pro A/V integrator a fully digital A/V interface. Extron Electronics take us through what it can and can’t do, its advantages and disadgantages and what it offers the integrator moving forward.
HDMI, or High Definition Multimedia Interface, is a digital A/V interface that supports high resolution computer-video and HDTV as well as multiple channels of audio on a single cable. It is prevalent in flat-panel displays and projectors as well as many consumer electronic products such as DVD and Blu-ray Disc players. For pro A/V applications, signal distribution devices are available including switchers and distribution amplifiers. HDMI enables a fully digital A/V pathway, delivering pristine, high quality computer-video and HDTV with no compression. HDMI and DVI utilize the high-speed digital video transmission standard known as TMDS, or Transition-Minimized Differential Signaling.
HDMI can offer advantages for pro A/V system integration. A digital pathway for video eliminates the need for D/A and A/D signal conversion, and a single HDMI cable can replace multiple cables. However, implementing HDMI in A/V systems has its own challenges, particularly with distributing signals. This article will explore HDMI, its capabilities, its advantages and disadvantages for pro A/V integration, products available for integrators, and what they will need to know when considering HDMI for their projects.
What are the capabilities of HDMI?
HDMI can deliver high resolution computer-video rates as high as WUXGA 1920x1200 and HDTV at 1080p, with 8-bit color depth. It supports up to eight channels of uncompressed audio at 24-bit/192 kHz, as well as the Dolby Digital and DTS compressed audio formats commonly used for DVDs, television broadcasts, and gaming.
The latest specification for HDMI, version 1.3, significantly increases video capabilities for future applications beyond HDTV, and will require support of data rates up to 10.2 Gbps, a twofold increase over 4.95 Gbps for previous versions. HDMI 1.3 supports resolutions beyond HDTV to WQXGA (2560x1600) and higher, as well as 10-bit, 12-bit, and 16-bit color depths – also known as Deep Color. Additionally, HDMI 1.3 adds support for a significantly increased color space known as x.v.Color, or the IEC 61966-2-4 xvYCC color standard that allows for reproduction of all colors visible to the human eye. For audio, HDMI 1.3 includes the Dolby and DTS lossless compression formats as part of Blu-ray Disc and HD DVD.
The HDMI standard also includes CEC, or Consumer Electronics Control. CEC enables an end user to command and control HDMI-equipped products from a single remote control, or a product to automatically command and control other CEC-enabled devices. Manufacturer implementation of CEC is optional.
HDCP, or High-bandwidth Digital Content Protection, is a technology for copy protection in which content transmitted between HDMI-equipped products is encrypted. It is of particular interest to content owners such as movie studios.
Consumer electronics products with HDMI are almost always HDCP-compliant for authorized playback of copyrighted content such as television broadcasts, Blu-ray Disc and HD DVD, and DVD from players that deliver upconverted output at HDTV resolutions. PCs and laptops with HDMI outputs generally are not expected to deliver HDCP-encrypted content, unless playing back copyrighted material such as Blu-ray Disc.
What can HDMI do for pro A/V integration?
HDMI enables an all-digital video pathway from the source to a flat-panel display or a projector, which helps to maintain high image quality throughout the system. Ultimately however, optimal presentation of high resolution video and graphics on-screen is dependent on proper set-up of the display as well as any scalers or signal processors in the system. If the incoming signal is analog, these devices need to be individually calibrated so that their internal video processing will be properly clocked and phased to the signal. This calibration should be performed for each incoming source, though in many installations the source, such as a laptop, is unknown and always changing.
However, if the display and video processors are HDMI-equipped, set-up is substantially simplified, since clocking and phasing are not necessary once an HDMI connection has been established. An HDMI infrastructure can help improve overall A/V system reliability and allow for consistent operation, without the uncertainty associated with bringing in new sources into the system.
HDMI has the potential to streamline integration, particularly in residential environments, by reducing cable requirements. A single cable connection delivers audio and video, replacing several cables. HDMI connections in A/V systems can simplify system designs and reduce the number of potential points of failure.
The connectors of HDMI cables are much smaller than those of DVI cables and are comparable to the size of RJ-45 connectors. Therefore, HDMI cables can conveniently be pulled through conduit and other restricted spaces. Since HDMI is fully backward-compatible with DVI for video, installations with DVI-equipped sources and displays as well as switchers and DAs can easily be integrated with newer HDMI cable as well as HDMI-equipped products.
What issues will an integrator face with HDMI?
HDMI signals can be transmitted over standard cabling up to 10 meters. Many integrators will find that this distance is not sufficient for many applications. Several products are available from Extron and others to increase the transmission distance to 60 meters and beyond through extenders, equalizers, and specialized, high performance cable.
HDMI requires a “handshake,†or connection, be established between the source and the destination – also known as “sink†– before transmission of signals is possible. First, the sink detects the presence of a newly connected source by sensing a Hot Plug Detect - HPD signal. Then, the source queries the sink for its requirements, including resolution and refresh rate, and then provides the appropriate signal. This occurs through the DDC, or Display Data Channel, and may also involve authentication if the content to be transmitted is copy-protected via HDCP. The protocol for communication between a source and a display is known as EDID, or Extended Display Identification Data.
Because of this requirement, distributing HDMI is not as straightforward as it would be for analogue RGB signals. With an HDMI distribution amplifier, it may be possible for a source to feed multiple displays simultaneously if they are identical. But what if they are different, and at various native resolutions? And what if the integrator wants to be able to route multiple sources to multiple displays via matrix switching? Many manufacturers offer products for HDMI distribution, and solutions for fully integrating HDMI into A/V systems continue to evolve.
Some integrators may face issues with compatibility between different HDMI-equipped products as well as with legacy displays with DVI ports. Some devices in use today may have HDMI interfaces from previous generations – versions prior to 1.2 – before the availability of full testing and validation for HDMI and HDCP compliance. The issue of inoperability between some HDMI-equipped products across various manufacturers is well-known in the electronics industry.
HDMI cables have stringent requirements for high speed data transmission as well as precision in their terminations. They are very difficult to terminate in the field, and as of yet no reliable tools exist to cut and terminate cables. Many integrators have also found that an HDMI cable connection is often not sufficiently secure. HDMI connectors do not have the locking screws of a DVI or VGA connector, though some manufacturers are beginning to offer connectors or boot assemblies with screw-down capability.
What solutions are available for integrating HDMI?
For sending HDMI signals beyond 10 meters, high performance HDMI cables are available at lengths of 30-45 meters or more, in some cases using fiber optic cable with the transmitter and receiver built into the connectors. Extron and other manufacturers offer extenders, products consisting of a transmitter and a receiver that send HDMI signals over CAT 5-type cables at lengths of at least 60 meters. Additionally, an HDMI cable equalizer can be attached to the end of a long HDMI cable run to help ensure signal integrity to the destination.
For distribution of HDMI signals, switchers and DAs are widely available, as well as some small-sized matrix switchers. To allow for connection between an HDMI source and multiple displays, DAs and matrix switchers are sometimes designed such that the source directly establishes DDC communications with one of the displays through one of the outputs. This EDID exchange is used as a reference and duplicated to multiple outputs, so that the source may feed multiple displays. However, this usually does not guarantee success, even when the displays are identical. If the content being delivered is copy-protected via HDCP, then establishing proper DDC communications is critical in order to be able to display content at all.
HDMI can also be integrated into A/V systems by way of scalers and signal processors that convert analog standard definition, HDTV, and high resolution RGB signals to HDMI. These devices can allow conventional A/V sources to be delivered to an HDMI-equipped display via a single cable, simplifying installation and potentially improving system reliability.
What should an integrator be aware of when working with HDMI?
Full implementation of HDMI in pro A/V systems is currently evolving. Manufacturers including Extron continue to develop solutions that will allow for reliable, robust routing and distribution of HDMI signals for facility-wide A/V integration.
Some compatibility issues may arise when integrating a system using HDMI products sourced from multiple manufacturers. To help optimize system reliability, integrators should probably stay within the same brand when specifying HDMI equipment for an A/V installation.
HDMI 1.3 is currently backward compatible with previous generations of HDMI. However, once available in future applications, enhancements in video capabilities specific to HDMI 1.3 will not be applicable to most current as well as legacy HDMI-equipped products. To accommodate the extra video bandwidth, HDMI 1.3 will require data speeds of 10.2 Gbps, a significant increase over the 4.95 Gbps maximum bit rate supported by previous generations of HDMI.
For more information about HDMI, there are further articles written by Steve Somers, Extron Vice President of Engineering available on the Extron website www.extron.com