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Education | Video Formats
SDI video
The serial digital interface is a format most commonly found
in high-end broadcasting applications. Although SDI transmits
uncompressed, unencrypted digital video signals, it typically
depends on 75-ohm BNC coax cable for transmission — the same
cabling traditionally used for analog video communications.
SDI interfaces are standardized by the Society of Motion Picture and
Television Engineers (SMPTE) and include: standard-definition SD-SDI
(SMPTE 259M) for 480i and 576i; “expanded” standard-definition ED-SDI
(SMPTE 344M) for 480p and 576p; high-definition HD-SDI (SMPTE
292M) for 720p and 1080i; and high-definition 3G-SDI (SMPTE 424M)
for 1080p transmitted at 2.970 Gbps.
DVI video
The Digital Video Interface (DVI) is a display technology
created by the Digital Display Working Group (DDWG).
Its design followed the VESA DFP connector standard,
and it was created to accommodate both analog and
digital interfaces
with a single connector. DVI is the standard digital interface for PCs (in
contrast to HDMI, which is more commonly found on HDTVs).
The format is based on transition-minimized differential signaling (TMDS).
Single-link DVI uses one TMDS-165 MHz transmitter, and dual-link DVI
uses two, doubling the transmission power. A single-link cable can
transmit a resolution of 1920 x 1200 vs. 2560 x 1600 for a dual-link cable.
The two most common DVI connector interfaces are:
DVI-D: This digital-only interface provides a high-quality image and
fast transfer rates. It eliminates analog conversion and
improves the display. Often used to link a source and
a display, it can be used when one or both
connections are DVI-D.
DVI-I: It integrates both digital and analog RGB support, and it can
transmit digital-to-digital or analog-to-analog signals. DVI-I can be
used with adapters to enable analog connectivity to a VGA or DVI-I
display or digital connectivity to a DVI-D display. You can achieve the
best picture quality by using a digital DVI display with a DVI-D video
source.
HDMI video
The High-Definition Multimedia Interface (HDMI
®
)
combines uncompressed HD video, multichannel audio,
and intelligent format/command data in a single cable with a very
compact connector.
HDMI can carry video at resolutions up to 4K x 2K (4096 x 2160 at 24 Hz).
It provides superior HDTV video and audio clarity and has enough
bandwidth (up to 5 Gigabytes) to spare for future applications. Plus, it’s
backward compatible with DVI (which simply ignores extra HDMI data).
HDMI also supports multiple audio formats from standard stereo to
multichannel surround sound. For video distribution applications, HDMI
provides two-way communications between the source and the digital TV,
enabling simple, remote, point-and-click configurations.
HDMI also supports High-bandwidth Digital Content Protection (HDCP),
which prevents the copying of content transmitted over HDMI cable. If you
have a device between the source and the display that supports HDMI but
not HDCP, your transmission won’t work, even over an HDMI cable.
HDMI offers significant benefits over older analog AV connections. It’s
backward compatible with DVI equipment. A DVI-to-HDMI adapter can be
used without a loss of video quality.
The HDMI standard was introduced in December 2002. Since then,
there have been a number of versions with increasing bandwidth and/or
transmission capabilities. Version 1.3, introduced in 2006, increased the
bandwidth to 10.2 Gbps and added support for up to 16-bit Deep Color.
Version 1.4, released in 2009, increased maximum supported resolution
to 4K x 2K (4096 x 2160 at 24 Hz), and added support for a 100-Mbps
Ethernet connection between the HDMI devices, an audio return channel,
and 3D support.
DisplayPort video
Designed by the Video Electronics Standards Association
(VESA), it competes directly with HDMI. Unlike HDMI,
however, DisplayPort is an open standard with no royalties.
This digital interface is used primarily between a computer and a monitor
or an HDTV and is built into many computer chipsets produced today.
It’s incredibly versatile, with the capability to deliver digital video, audio,
bidirectional communications, and accessory power over a single
connector.
DisplayPort v1.1 supports a maximum of 10.8 Gbps over a 6.4-foot (2-m)
cable; v1.2 supports up to 21.6 Gbps. DisplayPort v1.2 also enables you to
daisychain up to four monitors with only a single output cable. Plus, it offers
the future promise of DisplayPort hubs that would operate much like a
USB hub.
Cables up to 50 feet can be used for lower resolutions.
The standard DisplayPort connector is very compact and features latches
that don’t add to the connector’s size. Unlike HDMI, a DisplayPort
connector is easily lockable with a pinch-down locking hood. A quick
squeeze of
the connector releases the latch. Because it locks into place, accidental
disconnections are less likely — a quite useful feature for any video
distribution application where there’s digital signage in public areas.
DP++ compatible sources are able to output TMDS signals (HDMI or DVI
video) by using a compatible DisplayPort to HDMI or DVI adapter. HDMI
or DVI sources, on the other hand, require an active powered converter
to change the signal to DisplayPort.
DVI-D, Dual Link
4 If one connection is DVI and the other is VGA HD15,
you’ll need a cable or an adapter with both connectors.
4 To transmit embedded audio (without the need for a
separate audio run), use HDMI or DisplayPort devices.
4 A DVI-to-HDMI adapter can be used without a loss
of video quality.
4 Even with an HDMI cable plugged into a Blu-ray
player, devices in the distribution chain must be
HDCP compatible to display the video content.
4 If you require connections in high-vibration areas,
devices with DisplayPort connectors are a good choice.
4 Newer DisplayPort++ sources are able to output DVI
or HDMI signals using a simple adapter. This, however,
doesn’t work the other way around.
4 For advanced display technologies such as 4K, 3D,
and Deep Color, as well as outputting video on
WQXGA cinema monitors, use High-Speed HDMI
cable for connections.
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Digital Video Formats