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For example, an HD 1080 picture has 1080 lines (rows) of pixels. An odd field consists of pixel information for lines 1, 3, 5...1079. An even field has pixel information for lines 2, 4, 6...1080. When video is sent in interlaced-scan format, each frame is sent in two fields, the field of odd-numbered lines followed by the field of even-numbered ...
The compression ratio (that is, the size of the compressed file compared to that of the uncompressed file) of lossy video codecs is nearly always far superior to that of the audio and still-image equivalents. Video can be compressed immensely (e.g., 100:1) with little visible quality loss
The quality the codec can achieve is heavily based on the compression format the codec uses. A codec is not a format, and there may be multiple codecs that implement the same compression specification – for example, MPEG-1 codecs typically do not achieve quality/size ratio comparable to codecs that implement the more modern H.264 specification.
Most video coding standards, such as the H.26x and MPEG formats, typically use motion-compensated DCT video coding (block motion compensation). [70] [71] Most video codecs are used alongside audio compression techniques to store the separate but complementary data streams as one combined package using so-called container formats. [72]
Video compression schemes for Web and DVD make use of a 4:2:1 color sampling pattern, and the DV standard uses 4:1:1 sampling ratios. Professional video codecs designed to function at much higher bitrates and to record a greater amount of color information for post-production manipulation sample in 4:2:2 and 4:4:4 ratios.
XM (requires an eXternal electro-mechanical adapter) – Technically the same as EM, but such adapter usually consists of 2 parts: a pseudo-card with pin routing and physical enclosure size that perfectly match the target slot and a break-out box (a card reader) that holds a real card. Such adapter is the least comfortable to use.
Uncompressed video is digital video that either has never been compressed or was generated by decompressing previously compressed digital video. It is commonly used by video cameras, video monitors, video recording devices (including general-purpose computers), and in video processors that perform functions such as image resizing, image rotation, deinterlacing, and text and graphics overlay.
Software distributors use executable compression for a variety of reasons, primarily to reduce the secondary storage requirements of their software; as executable compressors are specifically designed to compress executable code, they often achieve better compression ratio than standard data compression facilities such as gzip, zip or bzip2 [citation needed].