Video resolution

Video resolution is one of those “fuzzy” things in life. It is common to see video resolutions quoted as “720×480” or “1920×1080.” 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 1440 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, this is 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” and “576i,” respectively.

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

Enhanced-Definition

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

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

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 (720 p) or 1080 interlaced (1080i) active scan lines. For a fixed-pixel (non-CRT) consumer display with a 16:9 aspect ratio, this translates into an active resolution of 1280×720 p or 1920×1080i, respectively.

However, HDTV displays are technically defined as being capable of displaying a minimum of 720 p or 1080i active scan lines. They also must be capable of displaying 16:9 content using a minimum of 540 progressive (540 p) or 810 interlaced (810i) active scan lines. This enables the manufacturing of CRT-based HDTVs with a 4:3 aspect ratio and LCD/plasma 16:9 aspect ratio displays with resolutions of 1024×1024 p, 1280×768 p, 1024×768 p, and so on, lowering costs.

Video and audio 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®, MPEG-1, or MPEG-2 audio.

MPEG-2 expanded on the original MPEG-1 video and audio compression to cover a much wider range of applications. The primary application targeted during the definition process was all-digital transmission of broadcast-quality video at bit-rates of 4 to 9 Mbps. However, MPEG-2 is useful for many other applications, such as HDTV, and now supports bit-rates of 1.5 to 60 Mbps.

MPEG-2 is an ISO standard that consists of eleven parts. As with MPEG-1, the compressed bitstreams implicitly define the decompression algorithms. The compression algorithms are up to the individual manufacturers, within the scope of the international standard.

Today, in addition to the legacy DV, MPEG-1, and MPEG-2 audio and video compression standards, there are three new high-performance video compression standards, which offer much higher video compression for a given level of video quality:

• MPEG-4.2 This video codec typically offers a 1.5 to 2 times improvement in compression ratio over MPEG-2. However, this standard has never achieved widespread acceptance due to its complexity. Many simply decided to wait for the new MPEG-4.10 (H.264) video codec to become available.
• MPEG-4.10 (H.264) This video codec typically offers a two to three times improvement in compression ratio over MPEG-2. Additional improvements in compression ratios and quality are expected as the encoder become better and use more of the available tools that H.264 offers. H.264 is optimized for implementing on low-cost single-chip solutions and has already been adopted by the DVB and ARIB.
• SMPTE 421 M (VC-1) A competitor to MPEG-4.10 (H.264), this video codec also typically offers a two to three times improvement in compression ratios over MPEG-2. Again, additional improvements in compression ratios and quality are expected as the encoders become better.