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Digital Video Formats

Digital Video Formats

SDI video

SDI ConnectorThe 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

DVI ConnectorThe 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

HDMI ConnectorThe 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

DisplayPort ConnectorDesigned 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 2-meter 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 15 meters 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.

Buyer's Tips

  • If one connection is DVI and the other is VGA HD15, you’ll need a cable or an adapter with both connectors.
  • To transmit embedded audio (without the need for a separate audio run), use HDMI or DisplayPort devices.
  • A DVI-to-HDMI adapter can be used without a loss of video quality.
  • 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.
  • If you require connections in high-vibration areas, devices with DisplayPort connectors are a good choice.
  • Newer DisplayPort++ sources are able to output DVI or HDMI signals using a simple adapter. This, however, doesn’t work the other way around.
  • 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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