Low-definition television

Low-definition television (LDTV) refers to television systems that have a lower screen resolution than standard-definition television systems. The term is usually used in reference to digital television, in particular when broadcasting at the same (or similar) resolution as low-definition analog TV systems. Mobile DTV systems usually transmit in low definition, as do all slow-scan TV systems.

The most common source of LDTV programming is the Internet, where mass distribution of higher-resolution video files could overwhelm computer servers and take too long to download. Many mobile phones and portable devices such as Apple’s iPod Nano, or Sony’s PlayStation Portable use LDTV video, as higher-resolution files would be excessive to the needs of their small screens (320×240 and 480×272 pixels respectively). The current generation of iPod Nanos have LDTV screens, as do the first three generations of iPod Touch and iPhone (480×320).

For the first years of its existence, YouTube offered only one, low-definition resolution of 320x240p at 30fps or less, only extending - first to widescreen 426×240, then to gradually higher resolutions - once the video service had become well established, it could afford radically improved storage space and transmission bandwidth, and could rely on a good proportion of its users having high-speed internet connections. More recently, YouTube has also extended further into the LDTV realm by adding an even lower 256×144p resolution with a halved framerate - giving an overall effect reminiscent of early online video streaming attempts using RealVideo or similar, where 160×120p at single-figure fps was deemed acceptable - to cater to those whose network connections could not even widthstand the rigors of "240p".

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