Nuts & Volts - January 2005

Video Basics

Video Resolution

Video resolution is one of those “fuzzy” things in life. It is common to see video resolutions of 720 x 480 or 1,920 x 1,080. However, those are just the number of horizontal samples and vertical scan lines and do not necessarily convey the amount of useful information.

For example, an analog video signal can be sampled at 13. 5 MHz to generate 720 samples per line. Sampling the same signal at 27 MHz would generate 1,440 samples per line. However, only the number of samples per line has changed, not the resolution of the content.

Therefore, video is usually measured using “lines of resolution.” In essence, how many distinct black-and-white vertical lines can be seen across the display? This number is then normalized to a 1:1 display aspect ratio (dividing the number by 3/4 for a 4: 3 display or by 9/16 for a 16: 9 display). Of course, this results in a lower value for widescreen (16: 9) displays, which goes against intuition.

Standard Definition

Standard definition video is usually defined as having 480 or 576 interlaced active scan lines and is commonly called 480i or 576i, respectively.

For a fixed-pixel (non-CRT) consumer display with a 4: 3 aspect ratio, this translates into an active resolution of 720 x 480i or 720 x 576i. For a 16: 9 aspect ratio, this translates into an active resolution of 960 x 480i or 960 x 576i.

Enhanced Definition

Enhanced definition video is usually defined as having 480 or 576 progressive active scan lines and is commonly called 480p or 576p, respectively.

For a fixed-pixel (non-CRT) consumer display with a 4: 3 aspect ratio, this translates into an active resolution of 720 x 480p or 720 x 576p. For a 16: 9 aspect ratio, this translates into an active resolution of 960 x 480p or 960 x 576p.

The difference between standard and enhanced definition is that standard definition is interlaced, while enhanced definition is progressive.

High Definition

High definition video is usually defined as having 720 progressive (720p) or 1,080 interlaced (1,080i) active scan lines. For a fixed-pixel (non-CRT) consumer display with a 16: 9 aspect ratio, this translates into an active resolution of 1,280 x 720p or 1,920 x 1,080i, respectively.

However, HDTV displays are technically defined as being capable of displaying a minimum of 720p or 1,080i active scan lines. They also must be capable of displaying 16: 9 content using a minimum of 540 progressive (540p) or 810 interlaced (810i) active scan lines. This enables the manufacturing of CRT-based HDTVs with 4: 3 aspect ratios and LCD/plasma 16: 9 aspect ratio displays with resolutions of 1,024 x 1,024p, 1,280 x 768p, 1,024 x 768p, and so on, lowering costs.

JANUARY 2005

Audio and Video Compression

The recent advances in consumer electronics — such as digital television, DVD players and recorders, digital video recorders, and so on — were made possible due to audio and video compression based largely on MPEG-2 video with Dolby^®Digital, DTS^®, or MPEG audio. New audio codecs (such as MPEG- 4 HE-AAC and WMA Pro) and new video codecs (such as H.264 and SMPTE VC-1) offer much better compression than legacy codecs for the same quality. These advances are enabling new ways of distributing content (both to consumers and within the home), new consumer products (such as portable video players and mobile video/cell phones), and more cable/satellite channels. NV

About the Author

Keith Jack is the author of Video Demystified and Director of Product Marketing at Sigma Designs, a leading supplier of Digital Media Processors that provides high quality processing of H.264, WMV9/VC-1, MPEG- 4, MPEG-2, MPEG-1, and content. In his previous career in marketing and chip design, he was involved in bringing over 30 multimedia chips to the consumer market.

Complete Ethernet Development Kit

KIT PRICE ^$99 Reg. ^$199

Breathe new life into your embedded systems with the Ethernet Connection Development Kit.

RCM3720 RabbitCore™ with 512K Flash,

256K SRAM, 1MB Serial Flash, 33 digital I/O. Complete development software (not a trial version). Royalty-free TCP/IP stack and sample programs/libraries. Development board with prototyping area. AC adapter and complete documentation.