SMPTE 292M
SMPTE 292 is a digital video transmission standard published by the Society of Motion Picture and Television Engineers (SMPTE) which expands upon SMPTE 259 and SMPTE 344 allowing for bit-rates of 1.485 Gbit/s, and 1.485/1.001 Gbit/s. These bit-rates are sufficient for and often used to transfer uncompressed high-definition video.
This standard is usually referred to as HD-SDI; it is part of a family of standards that define a Serial Digital Interface based on a coaxial cable, intended to be used for transport of uncompressed digital video and audio in a television studio environment.
The “M” designator was originally introduced to signify metric dimensions. It is no longer used in listings or filenames. Units of the International System of Units (SI) are the preferred units of measurement in all SMPTE Engineering Documents.
The SMPTE 292 standard is a nominally 1.5 Gbit/s interface. Two exact bitrates are defined; 1.485 Gbit/s, and 1.485/1.001 Gbit/s. The factor of 1/1.001 is provided to allow SMPTE 292 to support video formats with frame rates of 59.94 Hz, 29.97 Hz, and 23.98 Hz, in order to be upwards compatible with existing NTSC systems. The 1.485 Gbit/s version of the standard supports other frame rates in widespread use, including 60 Hz, 50 Hz, 30 Hz, 25 Hz, and 24 Hz.
The standard also defines nominal bitrates of 3 Gbit/s, for 50/60 frame per second 1080P applications. This version of the interface is not used (and has not been commercially implemented); instead, either a dual-link extension of SMPTE 292M known as SMPTE 372 or a version running twice as fast known as SMPTE 424 is used for e.g. 1080p60 applications.
Originally, both electrical and optical interfaces were defined by SMPTE, over concerns that an electrical interface at that bitrate would be expensive or unreliable, and that an optical interface would be necessary. Such fears have not been realized, and the optical interfaces are seldom if ever used, and are likely to be deprecated in future revisions of the standard.
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