HD Video, or High-Definition Video, is a video transmission system with a resolution higher than that of a Standard-Definition Video (SD Video). Whereas SD has fixed dimensions of 720x576 pixels for PAL and 720x480 pixels for NTSC, HD has two frame sizes – the smaller 1280x720 and the larger 1920x1080. The larger HD is today the predominant standard for TVs.
HD Video, introduced in 2004, was the first viable format for use in inexpensive cameras. Its two important features are – 1. It uses anamorphic stretching. This means that it uses curved lenses so that wider images can fit in a narrow frame, thus reducing the amount of data required. 2. It uses the MPEG-2 codec to compress and organize single frames into groups of frames, thus giving a better image and further reducing the amount of data.
H.261, introduced in 1990 by ITU (International Telecom Union), is one of the earlier video formats, now almost obsolete. It was developed for video conferencing over Public Switched Telephone Network (PSTN) to run at multiples of 64 Kbps data rates from 1x to 30x. H.261 was the first practical video codec and all the later standards have been based on this.
Different versions followed till H.264 was introduced in 2003. This version offers better compression efficiency and greater flexibility. It has the ability to predict macro-blocks based on data from other frames. This reduces the amount of information necessary to reproduce a video and gives a better picture quality.
In 2004, a better version of H.264 was released with new features like the Fidelity Range Extensions. This includes adaptive switching between 4x4 and 8x8 integer transforms, efficient inter-picture lossless coding, perceptual-based quantization weighting matrices, and support for additional color spaces. Further versions were released almost every year with more and better features, the latest being version 9, which was released in January 2009.
Today H.264 is considered the best scalable video coding system available, delivering excellent video quality across the entire bandwidth – including HD. For this reason H.264 is predominantly used in High-Definition Video.
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