Editing Serial digital interface (section)

==Electrical interface==
The various serial digital interface standards all use (one or more) [[coaxial cable]]s with [[BNC connector]]s, with a nominal impedance of 75 [[Ohm (unit)|ohms]]. 

This is the same type of cable used in analog [[composite video]] setups, potentially allowing for easier "drop-in" equipment upgrades (although, at high bitrates and/or long distances, it may be necessary for older, oxidising, or lower-grade cable to be replaced with [[Optical fiber connector|optical fibre]]). The specified signal amplitude at the source is 800 [[Volt|mV]] (±10%) peak-to-peak; far lower voltages may be measured at the receiver owing to [[attenuation]]. Using [[Equalization (communications)|equalization]] at the receiver, it is possible to send 270&nbsp;Mbit/s SDI over {{Convert|300|m|sp=us}} without use of repeaters, but shorter lengths are preferred. The HD bitrates have a shorter maximum run length, typically {{Convert|100|m|sp=us}}.<ref>{{cite book|title=Advice on the use of 3&nbsp;Gbit/s HD-SDI interfaces|date=July 2011|publisher=European Broadcasting Un|url=https://tech.ebu.ch/docs/techreports/tr002.pdf|access-date=20 July 2015}}</ref><ref>{{cite web|title=Recommended Transmission Distance at Serial Digital Data Rates|url=https://www.belden.com/resourcecenter/tools/upload/TB65_p28.pdf|website=Belden|access-date=20 July 2015|archive-url=https://web.archive.org/web/20150226050515/http://www.belden.com/resourcecenter/tools/upload/TB65_p28.pdf|archive-date=2015-02-26|url-status=dead}}</ref>

Uncompressed digital [[Component video|component]] signals are transmitted. Data is encoded in [[NRZI]] format, and a [[linear feedback shift register]] is used to [[scrambler|scramble]] the data to reduce the likelihood that long strings of zeroes or ones will be present on the interface. The interface is self-synchronizing and self-clocking. Framing is done by detection of a special [[synchronization]] pattern, which appears on the (unscrambled) serial digital signal to be a sequence of ten ones followed by twenty zeroes (twenty ones followed by forty zeroes in HD); this bit pattern is not legal anywhere else within the data payload.

===Standards===
{| class="wikitable"
|-
!Standard
!Name
!Introduced
!Bitrates (Mbit/s)
!Example video formats
|-
|[[SMPTE 259M]]
|SD-SDI
|1989<ref name=Hudson/>
|{{0|00}}270, 360, 143, 177
|480i, 576i
|-
|[[SMPTE 344M]]
|ED-SDI
|2000<ref>{{Cite web|url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1576-0-200206-W!!PDF-E.pdf|title=Transport of alternate source formats through Recommendation ITU-R BT.1120|website=International Telecommunication Union|access-date=February 27, 2019}}</ref>
|{{0|00}}540
|480p, 576p
|-
|[[SMPTE 292M]]
|HD-SDI
|1998<ref name=Hudson/>
|{{0}}1485 and 1485/1.001
|720p, 1080i
|-
|[[SMPTE 372M]]
|Dual Link HD-SDI
|2002<ref name=Hudson/>
|{{0}}2970 and 2970/1.001
|1080p60
|-
|[[SMPTE 424M]]
|3G-SDI
|2006<ref name=Hudson/>
|{{0}}2970 and 2970/1.001
|1080p60
|-
|SMPTE ST 2081
|6G-SDI
|2015<ref name="SDI2081March2015IEEE"/>
|{{0}}6000
|1080p120, 2160p30
|-
|SMPTE ST 2082
|12G-SDI
|2015<ref name="SDI2082March2015IEEE"/>
|12000
|2160p60
|-
|SMPTE ST 2083
|24G-SDI
|2020<ref name="SMPTE: 32NF-70 WG">{{Dead link|date=November 2017|cite web|url=https://kws.smpte.org/kws/public/projects/project/details?project_id=180|title=SMPTE: 32NF-70 WG Ultra HD SDI Interfaces|publisher=SMPTE}}</ref><ref>{{cite web|title=March 2014 Standards Quarterly Report (page 28)|url=https://www.smpte.org/sites/default/files/2014-03%20Niagra%20Outcome%20Report%20FINAL.pdf|website=SMPTE|access-date=19 September 2014|archive-date=16 July 2014|archive-url=https://web.archive.org/web/20140716042807/https://www.smpte.org/sites/default/files/2014-03%20Niagra%20Outcome%20Report%20FINAL.pdf|url-status=dead}}</ref>
|24000
|2160p120, 4320p30
|}

===Bit rates===
Several bit rates are used in serial digital video signal:

* For [[standard-definition]] applications, as defined by SMPTE 259M, the possible bit rates are 270&nbsp;Mbit/s, 360&nbsp;Mbit/s, 143&nbsp;Mbit/s, and 177&nbsp;Mbit/s. 270&nbsp;Mbit/s is by far the most commonly used; though the 360&nbsp;Mbit/s interface (used for [[widescreen]] standard definition) is sometimes encountered. The 143 and 177&nbsp;Mbit/s interfaces were intended for transmission of composite-encoded ([[NTSC]] or [[PAL]]) video digitally and are now considered obsolete.
* For [[enhanced definition television|enhanced definition]] applications (mainly 525P), there are several 540&nbsp;Mbit/s interfaces defined, as well as an interface standard for a dual-link 270&nbsp;Mbit/s interface. These are rarely encountered.
* For [[HDTV]] applications, the serial digital interface is defined by SMPTE 292M. Two bit rates are defined, 1.485&nbsp;Gbit/s, and 1.485/1.001&nbsp;Gbit/s. The factor of 1/1.001 is provided to allow SMPTE 292M to support video formats with frame rates of 59.94&nbsp;Hz, 29.97&nbsp;Hz, and 23.98&nbsp;Hz, in order to be compatible with existing [[NTSC]] systems. The 1.485&nbsp;Gbit/s version of the standard supports other frame rates in widespread use, including 60&nbsp;Hz, 50&nbsp;Hz, 30&nbsp;Hz, 25&nbsp;Hz, and 24&nbsp;Hz. It is common to collectively refer to both standards as using a nominal bit rate of 1.5&nbsp;Gbit/s.
* For very high-definition applications, requiring greater resolution, frame rate, or color fidelity than the HD-SDI interface can provide, the SMPTE 372M standard defines the '''dual link''' interface. As the name suggests, this interface consists of two SMPTE 292M interconnects operating in parallel. In particular, the dual link interface supports 10-bit, 4:2:2, 1080P formats at frame rates of 60&nbsp;Hz, 59.94&nbsp;Hz, and 50&nbsp;Hz, as well as 12-bit color depth, RGB encoding, and [[Chroma subsampling#4:4:4|4:4:4]] colour sampling.
* A nominal 3&nbsp;Gbit/s interface (more accurately, 2.97&nbsp;Gbit/s, but commonly referred to as "3 gig") was standardized by SMPTE as 424M in 2006. Revised in 2012 as SMPTE ST 424:2012, it supports all of the features supported by the dual 1.485&nbsp;Gbit/s interface but requires only one cable rather than two.

===Other interfaces===
SMPTE 297-2006 defines an optical fiber system for transmitting bit-serial digital signals It is intended for transmitting SMPTE ST 259 signals (143 through 360&nbsp;Mbit/s), SMPTE ST 344 signals (540&nbsp;Mbit/s), SMPTE ST 292-1/-2 signals (1.485&nbsp;Gbit/s and 1.485/1.001&nbsp;Gbit/s) and SMPTE ST 424 signals (2.970&nbsp;Gbit/s and 2.970/1.001&nbsp;Gbit/s). In addition to optical specification, ST 297 also mandates laser safety testing and that all optical interfaces are labelled to indicate safety compliance, application and interoperability.<ref>{{Cite web|url=https://www.smpte.org/sites/default/files/2013-09-10-3GSDI-Hudson-V3-Full.pdf|title=3Gb/s SDI for Transport of 1080p50/60, 3D, UHDTV1 / 4k and Beyond|last=SMPTE|date=2013|access-date=2017-03-17|archive-date=2016-03-03|archive-url=https://web.archive.org/web/20160303225904/https://www.smpte.org/sites/default/files/2013-09-10-3GSDI-Hudson-V3-Full.pdf|url-status=dead}}</ref>

An 8-bit parallel digital interface is defined by [[Rec. 601|ITU-R Rec. 601]]; this is obsolete (however, many clauses in the various standards accommodate the possibility of an 8-bit interface).