video formats

A video format describes how one device sends video pictures to another device, such as the way that a DVD player sends pictures to a television, or a computer to a monitor. More formally, the video format describes the sequence and structure of frames that create the moving video image.

Video formats are commonly known in the domain of commercial broadcast and consumer devices; most notably to date, these are the analog video formats of NTSC, PAL, and SECAM. However, video formats also describe the digital equivalents of the commercial formats, the aging custom military uses of analog video (such as RS-170 and RS-343), the increasingly important video formats used with computers, and even such offbeat formats such as color field sequential.

Video formats were originally designed for display devices such as a CRTs. However, because other kinds of displays have common source material and because video formats enjoy wide adoption and have convenient organization, video formats are a common means to describe the structure of displayed visual information for a variety of graphical output devices.

Common organization of video formats

A video format describes a rectangular image carried within an envelope containing information about the image. Although video formats vary greatly in organization, there is a common taxonomy:

• A frame can consist of two or more fields, sent sequentially, that are displayed over time to form a complete frame. This kind of assembly is known as interlace. An interlaced video frame is distinguished from a progressive scan frame, where the entire frame is sent as a single intact entity.
• A frame consists of a series of lines, known as scan lines. Scan lines have a regular and consistent length in order to produce a rectangular image. This is because in analog formats, a line lasts for a given period of time; in digital formats, the line consists of a given number of pixels. When a device sends a frame, the video format specifies that devices sends each line independently from any others and that all lines are sent in top-to-bottom order.

• As above, a frame may be split into fields – odd and even (by line "numbers") or upper and lower, respectively. In NTSC, the lower field comes first, then the upper field, and that's the whole frame. The basics of a format are Aspect Ratio, Frame Rate, and Interlacing with field order if applicable: Video formats use a sequence of frames in a specified order. In some formats, a single frame is independent of any other (such as those used in computer video formats), so the sequence is only one frame. In other video formats (such as the Bruch sequence in PAL), frames have an ordered position. Individual frames within a sequence typically have similar construction. However, depending on its position in the sequence, frames may vary small elements within them to represent additional information. For example, MPEG-2 compression, may eliminate the information that is redundant frame-to-frame in order to reduce the data size, preserving the information relating to changes between frames. See Video Compression for further explanation, and particularly I-frame or Key-frame.

Analog video formats

• NTSC
• PAL
• SECAM

Blanking region

The video format consists of more information than the visible content of the frame. Preceding and following the image are lines and pixels containing synchronization information or a time delay. This surrounding margin is known as a blanking interval; the horizontal and vertical front porch and back porch are the building blocks of the blanking interval.

Digital Video Formats

These are MPEG2 based terrestrial broadcast video fomats

• ATSC Standards
• DVB
• ISDB

These are strictly the format of the video itself, and not for the modulation used for transmission.

See List of codecs

Donate to Wikimedia