Digital Video Connections 101

What's the first thing you think of when you hear someone say "digital video"? It is a term getting used more frequently - especially with the upcoming analog shutoff - but there is still a lot of misconceptions about what digital video is. The biggest of these misconceptions is that digital video is the same thing as high-definition video. Digital video is not necessarily in high definition, but HD video is usually sent with a digital signal. That is not always true however, as we saw in last week's post, some analog connections are capable of transmitting HD video.

The main difference between analog video and digital video is that analog is sent as a radio wave, while digital is sent as a series of 1's and 0's. By sending the signal this way, there is no quality loss as the binary string will still be the same when it reaches the other end. This lends itself to another one of the major benefits of digital video - it is much easier to distribute. Analog video depends on film and tape, while digital video can be copied and sent electronically much easier.

Below are the different types of connections used to transfer digital video. Some are used in conjunction with cameras and PCs, while others are used in home theater setups.

USB (Universal Serial Bus)
USB is a system of connecting multiple devices to a computer at once with little setup necessary besides plugging it in. USB has many other uses besides transferring video; it is included here even though there are faster connections available because virtually all current computers have multiple USB connections. USB 2.0 was released in 2000 with an increased data transfer rate to 480 megabits per second, which is 40 times faster than the previous version USB 1.1. USB is not used as television connector because it does not have enough bandwidth to send an HD signal in real time.

Firewire (IEEE 1394)
Firewire goes by many names including Sony i.LINK and IEEE 1394, which is the official name of the connector. Firewire was designed by Apple in 1995 as an alternative to USB, which at the time was rather slow. Firewire's original data transfer rate (400 Mbps) was much faster than USB 1.1. USB 2.0 closed the gap but was followed by a revision to the Firewire standard, bumping it's bandwidth up to 800 Mbps. Firewire's main use is in transferring digital video from camcorders to computers for later editing.

DVI (Digital Video Interface)
DVI connections are a computer's answer to the analog / digital switch. Computer monitors were originally created with the same cathode ray tube technology as televisions. CRT monitors display video as an analog signal, so the analog VGA connection used for over a decade with PCs was fine. As Liquid Crystal Displays (LCD) started to hit the market, a new type of digital connection was needed. Sure, many LCD displays have VGA inputs and your analog VGA cable will work fine with them, but there is a catch. The computer sends the info digitally and the monitor displays the image digitally. If you're using an analog cable, the computer will have to convert the signal to analog, send it over the cable, and then the monitor must convert it back to digital before it can display the picture.

HDMI (High Definition Multimedia Interface)
The biggest advantage of HDMI over DVI is that an HDMI cable can carry audio as well as video. The video signal in an HDMI cable is sent the same way as in the DVI cable, which makes them compatible with each other. HDMI connections are even starting to replace DVI connections on some high-end graphics cards and monitors, which will only continue to blur the line between television and computers. HDMI is considered the future of digital video, but all HDMI connections are not created equal. HDMI is currently at version 1.3b with talk of HDMI 1.4 in the works. Check back soon for an in depth explanation of the different HDMI versions.

Resources:
HDTV Connection Type
Audio/Visual Signal Protocols