With the rise of high definition video content and the adoption of HDTV, the need for a standard unified connector was needed. The DVI interface was originally developed for computer systems and was placed on early HDTV units, but there are a number of limitations with it that manufacturers looked to put together a newer connector. From this, the High Definition Multi-media Interconnect or HDMI standards were developed.
This article looks at some of the features of the HDMI interface in relation to the older DVI interface and compares it to alternative digital video connectors used in computer systems.
Smaller Standardized Connectors
One of the big advantages of the HDMI interface over the DVI interface is the size of the connector. The DVI interface is similar in size to the older VGA interface at roughly 1.5 inches in width. The standard HDMI connector is roughly one third the size of the DVI connector. The HDMI version 1.3 specification added support for a smaller mini-HDMI connector which was useful for the extremely thin laptops and smaller consumer electronics like cameras. With HDMI version 1.4, the micro-HDMI connector was added with an even smaller connector that was useful for the growing use of tablet and smarthphone devices.
Audio and Video on a Single Cable
The cable advantages of HDMI become even more pronounced over DVI because HDMI also carries digital audio. With most home computers using at least one and possible up to three mini-jack cables to run audio from it to the speakers, the HDMI cable simplifies the number of cables require to carry the audio signal to the monitor. In the original HDMI implementations of graphics cards, audio passthrough connectors were used to add the audio stream to the graphics cards but most now also feature sound drives to handle both audio and video at the same time.
While audio and video on a single cable was unique when HDMI was first intorduced, this feature was also implemented into the DisplayPort video connector. Since that has occurred, the HDMI group has worked on expanding the support for additional multi-channel audio. This includes 7.1 audio in the HDMI version 1.4 and now up to a total of 32 audio channels with the latest HDMI version 2.0.
Increased Color Depth
Analog and digital color for PC computers has long been restricted to 24-bit color producing roughly 16.7 million colors. This is generally considered true color because the human eye can't distinguish between the shades easily. With the increased resolution of HDTV, the human eye can tell a difference in overall quality of color between 24-bit color depth and higher levels, even if it can't distinguish the individual colors.
DVI is limited to this 24-bit color depth. Early HDMI versions are also limited to this 24-bit color, but with version 1.3 color depths of 30, 36 and even 48-bit were added. This greatly increases the overall quality of the color that can be displayed, but both the graphics adapter and monitor must support the HDMI version 1.3 or higher. In contrast, the DisplayPort also introduced expanded color depth support up to the 48-bit color depth.
One of the big requirements for the high definition DVD and TV signals is a digital rights management signal. This allows the rights holder to ensure that a digital copy of the material cannot be capture before it reaches the video display. At this point, all devices now support this digital rights standard. If you attempt to use something that requires a HDCP verified connection between the graphics card and the display device but don't have it, the video signal is generally dropped to a black screen or an error message stating the hardware requirements. This isn't too much of an issue with current HDMI hardware but some early gear may not support it.
The DVI video standard did not require that the HDCP or high definition copy protection signal be supported by the devices. As a result, many PC computers and monitors that feature the DVI connector may be locked out from the high definition content. Some video card and display manufacturers do support the HDCP signal with the DVI devices, but it can be hard to ensure that your hardware is compliant.
HDMI has this HDCP built into the standard. As a result, any HDMI capable graphics card and monitor must have this feature. This prevents the potential problem in the future of restricted or non-functional digital video from the PC. DisplayPort is fully compliant with HDCP standards.
One of the most important features included with the HDMI standard is the ability for it to be used with DVI connectors. Through the use of an adapter cable, an HDMI plug can be attached to a DVI monitor port for the video signal. This is a very useful feature for those that do purchase a system with an HDMI compliant video output but their television or computer monitor only has a DVI input. It should be noted that this only uses the video portion of the HDMI cable so no audio can be used with it. In addition, while a monitor with a DVI connector can connect to a HDMI graphics port on the computer, a HDMI monitor cannot connect to a DVI graphics port on the computer.
DisplayPort does not have as much flexibility in this area. In order to use DisplayPort with other video conectors, an active dongle connector is required to convert the video signal from the Displayport standard to HDMI, DVI or VGA. These connectors can be quite expensive and is a major drawback to the DisplayPort connector.
Standard vs. High Speed Cables
The HDTV industry tried to spur continued consumer demand with a huge push for 3D video content. The goal was to provide a more immersive environment for the viewing. With the added data requirements to carry the extra signal necessary to generate the 3D image, the HDMI standard groups introduced the version 1.4 standard. This added the necessary data bandwidth for 3D HDTV but it also introduced several different style of cables. They look nearly identical but eletrically they are quite different just like Ethernet cables couldbe designed for Fast or Gigabit speeds.
Essentially there are two different classes of cables, standard or high speed (also called category 2). The standard cable works perfectly fine for delaing with standard 720p or 1080p video with multichannel audio. The high speed HDMI cables are necessary for any application that uses resolutions above 1080p, 3D video or the deep color channels that were mentioned above. In addition to these, you can also have standard or high speed cables with or without Ethernet ability. Essentially, this type of cable adds an additional data cable component that allows for standard computer networking between two devices. It should be noted that both ends of the cable must support the feature as well as the cable. The Ethernet style cables are very uncommon as it is not support by many consumer devices.
If you do happen to have HDMI devices, it is best to use high speed rated cables as they are fully backwards compatible but allow for future hardware changes without the need for new cables.
Version 2.0 Additions
With the rise of UltraHD or 4K Displays, there are some major bandwidth requirements in order to carry all of the data necessary for such a high resolution display. The HDMI version 1.4 standards were able to go up to the 2160p resolutions requires but only at 30 frames per second. This was a major shortcoming compared to the DisplayPort standards. Thankfully, the HDMI working group released version 2.0 before the bulk of 4K displays reached market. In addition to the high frame rates at the UltraHD resolutions, it also supports:
- Ability to have two (1080p) video streams carried over a single cable.
- Improved audio sampling rates for improve sound fideltiy.
- Ability to carry four audio streams to multiple users across a single cable.
- Support for 21:9 aspect ratio video for wider screen displays.
- Dynamic audio to video sychornoication.
- Support for command and control extensions for mutliple device control through a single device.
Most of these features have yet to be integrated into home consumer electronics or computer systems but they do have significant potential for users that may need to share a computer device, display or audio setup.
Should You Look at HDMI on a Computer System?
At this point, all consumer laptop and desktop computers should come with an HDMI port standard. This makes it very easy to use them with your standard digital computer monitors and HDTVs. It should be noted that there are still a few budget class computers on the market that do not feature this connector. I would probably avoid these computers as it can be a liability in the future. In addition to this, some corporate class computers may not feature the HDMI port but instead come with a DisplayPort. This is a suitable alternative but you need to make sure you have a monitor that can support that connector.
The issue with HDMI support is more for tablet computers and smartphones. This is not something that is standard to them but you may want support for a micro or mini-HDMI connector so that it can be hooked up to a HDTV for streaming or playback of video content.