[6] Dual link HD-SDI consists of a pair of SMPTE 292M links, standardized by SMPTE 372M in 1998;[2] this provides a nominal 2.970 Gbit/s interface used in applications (such as digital cinema or HDTV 1080P) that require greater fidelity and resolution than standard HDTV can provide.

[7][8] These standards are used for transmission of uncompressed, unencrypted digital video signals (optionally including embedded audio and time code) within television facilities; they can also be used for packetized data.

SDI is used to connect together different pieces of equipment such as recorders, monitors, PCs and vision mixers.

[citation needed] The various serial digital interface standards all use (one or more) coaxial cables with BNC connectors, with a nominal impedance of 75 ohms.

This is the same type of cable used in analog composite video setups, which potentially makes for easier "drop in" equipment upgrades (though may be necessary for long runs at the higher bitrates for older oxidising or lower grade of cable to replaced which may be replaced via optical fibre for long distance in modern use).

The specified signal amplitude at the source is 800 mV (±10%) peak-to-peak; far lower voltages may be measured at the receiver owing to attenuation.

Using equalization at the receiver, it is possible to send 270 Mbit/s SDI over 300 meters (980 ft) without use of repeaters, but shorter lengths are preferred.

The HD bitrates have a shorter maximum run length, typically 100 meters (330 ft).

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.

Cr and Cb further refer to the red and blue "color difference" channels; see Component video for more information.

In the HD-SDI and dual link interfaces, synchronization packets must occur simultaneously in both the Y and C datastreams.

The link number of a given interface is indicated by a VPID packet located in the vertical ancillary data space.

Ancillary data is provided as a standardized transport for non-video payload within a serial digital signal; it is used for things such as embedded audio, closed captions, timecode, and other sorts of metadata.

Ancillary data is indicated by a 3-word packet consisting of 0, 3FF, 3FF (the opposite of the synchronization packet header), followed by a two-word identification code, a data count word (indicating 0–255 words of payload), the actual payload, and a one-word checksum.

Specific applications of ancillary data include embedded audio, EDH, VPID and SDTI.

SMPTE ST 299-2:2010 extends the 3G SDI interface to be able to transmit 32 audio channels (16 pairs) on a single link.

As the standard definition interface carries no checksum, CRC, or other data integrity check, an EDH (Error Detection and Handling) packet may be optionally placed in the vertical interval of the video signal.

In early versions of the serial digital interface, it was always possible to uniquely determine the video format by counting the number of lines and samples between H and V transitions in the TRS.

The default (and most common case) is 10-bit linearly sampled video data encoded as 4:2:2 YCbCr.

Data words correspond to signal levels of the respective video components, as follows: Note that the scaling of the luma and chroma channels is not identical.

12-bit applications are scaled in a similar fashion to their 10-bit counterparts; the additional two bits are considered to be LSBs.

The asynchronous serial interface (ASI) specification describes how to transport a MPEG Transport Stream (MPEG-TS), containing multiple MPEG video streams, over 75-ohm copper coaxial cable or multi-mode optical fiber.

ASI is popular way to transport broadcast programs from the studio to the final transmission equipment before it reaches viewers sitting at home.

This standard allows, for example, several independent standard-definition video signals to be multiplexed onto an HD-SDI interface and transmitted down one wire.

This standard doesn't merely adjust EAV and SAV timing to meet the requirements of the lower-bitrate formats; instead, it provides a means by which an entire SDI format (including synchronization words, ancillary data, and video payload) can be encapsulated and transmitted as ordinary data payload within a 292M stream.

It is mainly used in the consumer area, but increasingly used in professional devices including uncompressed video, often called clean HDMI.