Video interfaces
May 1, 2009 12:00 PM, By Aldo Cugnini
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DisplayPort is a relatively recent license-free digital audio/video interconnect, proposed by VESA to succeed DVI; it's primarily intended to be used between a computer and its display monitor. Because it's based on a micro-packet protocol, DisplayPort may have an advantage over other interfaces by easing future expansion of the standard. The interface consists of a unidirectional main link for connecting A/V streams from source devices to sink devices, and a half-duplex bidirectional auxiliary channel used for realizing plug-and-play features such as equipment control. The main link may have one, two or four differential signal pairs (or lanes), offering a total raw capacity of up to 10.8Gb/s. Computer giant Dell is a strong DisplayPort supporter, and rumors have it that the company will include the interface on all products within two years.
Traditional USB 2.0 (high-speed USB) has already become the interface of choice for many computer peripherals, including storage media. It supports a maximum transfer rate of 480Mb/s. The new USB 3.0 specification (Super Speed) has already been completed, and USB 3.0 products are expected in late 2009. This version will increase transfer rates up to 5Gb/s.
Where's it all going?
Most production and broadcast video systems now include SD/HD-SDI, which supports up to 720p/1080i (uncompressed), and marketplace evidence suggests that video equipment is transitioning from HD-SDI to 3Gig-SDI. With 1080p video becoming the dominant video format in the future (and possibly the current de-facto production standard), transmission speed will be the bottleneck in any video interface. Research over the last two years has shown that 1080p can be done at an equivalent bit rate to current 1080i broadcasts, provided MPEG-4 (H.264/AVC) is used.
Despite the proliferation of displays with HDMI or DVI interfaces, studios will still need to test video quality on legacy analog TVs and monitors. So, don't count out analog component video interfaces — yet.
Aldo Cugnini is a consultant in the digital television industry.
Table 1. 3Gig-SDI supported video formats, per SMPTE-425M
| Picture format | Signal format | Progressive frame rate | Interlaced field rate |
|---|---|---|---|
| 1920 × 1080 | 10-bit 4:2:2 (Y'C'BC'R) | 60, 59.94, 50 | |
| 10-bit* 4:4:4 (R'G'B') 4:4:4:4 (R'G'B' + A) 4:4:4 (Y'C'BC'R) 4:4:4:4 (Y'C'BC'R + A) | 30, 29.97, 25, 24, 23.98 | 60, 59.94, 50 | |
| 12-bit 4:4:4 (R'G'B') 4:4:4 (Y'C'BC'R) 4:2:2 (Y'C'BC'R)* | |||
| 1280 × 720 | 10-bit 4:4:4 (Y'C'BC'R) 4:4:4:4 (Y'C'BC'R + A) 4:4:4 (R'G'B') 4:4:4:4 (R'G'B' + A) | 60, 59.94, 50, 30, 29.97, 25, 24, 23.98 | |
| 2048 × 1080 (D-Cinema) | 12-bit 4:4:4 (X'Y'Z')* | 24 | |
| * Includes PsF (Progressive segmented Frame) format | |||
Send questions and comments to: aldo.cugnini@penton.com
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