Serial Digital Interface - AbsoluteAstronomy.com

Serial digital interface (SDI) is a family of video

Video

Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...

interfaces standardized by SMPTE. For example, ITU-R

ITU-R

The ITU Radiocommunication Sector is one of the three sectors of the International Telecommunication Union and is responsible for radio communication....

BT.656 and SMPTE 259M

SMPTE 259M

SMPTE 259M is a standard published by SMPTE which "... describes a 10-bit serial digital interface operating at 143/270/360 Mb/s." The goal of SMPTE 259M is to define a Serial Digital Interface , called SDI or SD-SDI....

define digital video

Video

Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...

interfaces used for broadcast

Broadcasting

Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...

-grade video. A related standard, known as high-definition serial digital interface (HD-SDI), is standardized in SMPTE 292M

SMPTE 292M

SMPTE 292M is a standard published by SMPTE which expands upon SMPTE 259M and SMPTE 344M allowing for bit-rates of 1.485 Gbit/s, and 1.485/1.001 Gbit/s...

; this provides a nominal data rate of 1.485 Gbit/s.

An emerging interface, commonly known in the industry as dual link HD-SDI and consisting essentially of a pair of SMPTE 292M links, is standardized in SMPTE 372M

SMPTE 372M

SMPTE 372M is a standard published by SMPTE which expands upon SMPTE 259M, SMPTE 344M, and SMPTE 292M allowing for bit-rates of 2.970 Gbit/s, and 2.970/1.001 Gbit/s over two wires. These bit-rates are sufficient for 1080p video....

; this provides a nominal 2.970 Gbit/s interface used in applications (such as digital cinema

Digital cinema

Digital cinema refers to the use of digital technology to distribute and project motion pictures. A movie can be distributed via hard drives, optical disks or satellite and projected using a digital projector instead of a conventional film projector...

or HDTV 1080P) that require greater fidelity and resolution than standard HDTV can provide. A more recent interface, 3G-SDI, consisting of a single 2.970 Gbit/s serial link, is standardized in SMPTE 424M

SMPTE 424M

"SMPTE 424M" is a standard published by SMPTE which expands upon SMPTE 259M, SMPTE 344M, and SMPTE 292M allowing for bit-rates of 2.970 Gbit/s and 2.970/1.001 Gbit/s over a single-link coaxial cable. These bit-rates are sufficient for 1080p video at 50 or 60 frames per second...

that will replace the dual link HD-SDI.

These standards are used for transmission of uncompressed, unencrypted digital video signals (optionally including embedded Audio and/or Time Code) within television facilities; they can also be used for packetized data. Coaxial variants of the specification range in length but are typically less than 300 meters. Fiber optic variants of the specification such as 297M allow for long-distance transmission limited only by maximum fiber length and/or repeaters. SDI and HD-SDI are currently only available in professional video equipment; various licensing agreements, restricting the use of unencrypted digital interfaces to professional equipment, prohibit their use in consumer equipment. There are various mod kits for existing DVD player

DVD player

A DVD player is a device that plays discs produced under both the DVD-Video and DVD-Audio technical standards, two different and incompatible standards. These devices were invented in 1997 and continue to thrive...

s and other devices, which allow a user to add a serial digital interface to these devices.

Electrical interface

The various serial digital interface standards all use (one or more) coaxial

Coaxial

In geometry, coaxial means that two or more forms share a common axis; it is the three-dimensional linear analogue of concentric.Coaxial cable, as a common example, has a wire conductor in the centre a circumferential outer conductor and an insulating medium called the dielectric separating...

cables with BNC connector

BNC connector

The BNC connector ' is a common type of RF connector used for coaxial cable. It is used with radio, television, and other radio-frequency electronic equipment, test instruments, video signals, and was once a popular computer network connector. BNC connectors are made to match the characteristic...

s, with a nominal impedance of 75 ohms. This is the same type of cable used in analog video setups, which potentially makes for easier upgrades (though higher quality cables may be necessary for long runs at the higher bitrates). The specified signal amplitude at the source is 800 mV

Volt

The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...

(±10%) peak-to-peak; far lower voltages may be measured at the receiver owing to attenuation

Attenuation

In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...

. Using equalisation at the receiver

Receiver (radio)

A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...

, it is possible to send 270 Mbit/s SDI over 300 metres without use of repeaters, but shorter lengths are preferred. The HD bitrates have a shorter maximum run length, typically 100 meters.

Uncompressed digital component

Component video

Component video is a video signal that has been split into two or more component channels. In popular use, it refers to a type of component analog video information that is transmitted or stored as three separate signals...

signals are transmitted. Data is encoded in NRZI format, and a linear feedback shift register

Linear feedback shift register

A linear feedback shift register is a shift register whose input bit is a linear function of its previous state.The most commonly used linear function of single bits is XOR...

is used to 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

Synchronization

Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....

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

Standard	Name	Bitrates	Example Video Formats
SMPTE 259M SMPTE 259M SMPTE 259M is a standard published by SMPTE which "... describes a 10-bit serial digital interface operating at 143/270/360 Mb/s." The goal of SMPTE 259M is to define a Serial Digital Interface , called SDI or SD-SDI....	SD-SDI	270 Mbit/s, 360 Mbit/s, 143 Mbit/s, and 177 Mbit/s	480i, 576i
SMPTE 344M SMPTE 344M "SMPTE 344M" is a standard published by SMPTE which expands upon SMPTE 259M allowing for bit-rates of 540 Mbit/s, allowing EDTV resolutions of 480p and 576p.This standard is part of a family of standards that define a Serial Digital Interface....	ED-SDI	540 Mbit/s	480p, 576p
SMPTE 292M SMPTE 292M SMPTE 292M is a standard published by SMPTE which expands upon SMPTE 259M and SMPTE 344M allowing for bit-rates of 1.485 Gbit/s, and 1.485/1.001 Gbit/s...	HD-SDI	1.485 Gbit/s, and 1.485/1.001 Gbit/s	720p, 1080i
SMPTE 372M SMPTE 372M SMPTE 372M is a standard published by SMPTE which expands upon SMPTE 259M, SMPTE 344M, and SMPTE 292M allowing for bit-rates of 2.970 Gbit/s, and 2.970/1.001 Gbit/s over two wires. These bit-rates are sufficient for 1080p video....	Dual Link HD-SDI	2.970 Gbit/s, and 2.970/1.001 Gbit/s	1080p
SMPTE 424M SMPTE 424M "SMPTE 424M" is a standard published by SMPTE which expands upon SMPTE 259M, SMPTE 344M, and SMPTE 292M allowing for bit-rates of 2.970 Gbit/s and 2.970/1.001 Gbit/s over a single-link coaxial cable. These bit-rates are sufficient for 1080p video at 50 or 60 frames per second...	3G-SDI	2.970 Gbit/s, and 2.970/1.001 Gbit/s	1080p

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 Mbit/s, 360 Mbit/s, 143 Mbit/s, and 177 Mbit/s. 270 Mbit/s is by far the most commonly used; though the 360 Mbit/s interface (used for widescreen
Widescreen
Widescreen images are a variety of aspect ratios used in film, television and computer screens. In film, a widescreen film is any film image with a width-to-height aspect ratio greater than the standard 1.37:1 Academy aspect ratio provided by 35mm film....

standard definition) is sometimes encountered. The 143 and 177 Mbit/s interfaces were intended for transmission of composite-encoded (NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...

or PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...

) video digitally, and are now considered obsolete.
For enhanced definition applications (mainly 525P), there are several 540 Mbit/s interfaces defined, as well as an interface standard for a dual-link 270 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 Gbit/s, and 1.485/1.001 Gbit/s. The factor of 1/1.001 is provided to allow SMPTE 292M to support video formats with frame rates of 59.94 Hz, 29.97 Hz, and 23.98 Hz, in order to be compatible with existing NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...

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. It is common to collectively refer to both standards using a nominal bit rate of 1.5 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 Hz, 59.94 Hz, and 50 Hz, as well as 12-bit color depth, RGB encoding, and 4:4:4 colour sampling.
A nominal 3 Gbit/s interface (more accurately, 2.97 Gbit/s, but commonly referred to as "3 gig") is standardized by SMPTE; , chipsets for this interface are just becoming available. It is intended to support all of the features supported by the dual 1.485 Gbit/s interface, but requires only one cable rather than two.

Other interfaces

SMPTE 297-2006 defines an optical interface for SDI. An 8-bit parallel digital interface is defined by ITU-R Rec. 601; this is obsolete (however, many clauses in the various standards accommodate the possibility of an 8-bit interface).

Data Format

In SD and ED applications, the parallel data format is defined to 10 bits wide, whereas in HD applications, it is 20 bits wide, divided into two parallel 10-bit datastreams (known as Y and C). The SD datastream is arranged like this:

Cb Y Cr Y' Cb Y Cr Y'

whereas the HD datastreams are arranged like this:

Y: Y Y' Y Y' Y Y' Y Y'
C: Cb Cr Cb Cr Cb Cr Cb Cr

For all serial digital interfaces (excluding the obsolete composite encodings), the native color encoding is 4:2:2 YCbCr

YCbCr

YCbCr or Y′CbCr, sometimes written or , is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the luma component and CB and CR are the blue-difference and red-difference chroma components...

format. The luminance channel (Y) is encoded at full bandwidth (13.5 MHz in 270 Mbit/s SD, ~75 MHz in HD), and the two chrominance channels (Cb and Cr) are subsampled horizontally, and encoded at half bandwidth (6.75 MHz or 37.5 MHz). The Y, Cr, and Cb samples are co-sited (acquired at the same instance in time), and the Y' sample is acquired at the time halfway between two adjacent Y samples.

In the above, Y refers to luminance

Luminance

Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...

samples, and C to chrominance

Chrominance

Chrominance is the signal used in video systems to convey the color information of the picture, separately from the accompanying luma signal . Chrominance is usually represented as two color-difference components: U = B' − Y' and V = R' − Y'...

samples. Cr and Cb further refer to the red and blue "color difference" channels; see Component Video

Component video

for more information. This section only discusses the native color encoding of SDI; other color encodings are possible by treating the interface as a generic 10-bit data channel. The use of other colorimetry encodings, and the conversion to and from RGB colorspace, is discussed below.

Video payload (as well as ancillary data payload) may use any 10-bit word in the range 4 to 1019 (004 to 3FB in hexadecimal) inclusive; the values 0-3 and 1020-1023 (3FC - 3FF) are reserved and may not appear anywhere in the payload. These reserved words have two purposes; they are used both for Synchronization packets and for Ancillary data headers.

Synchronization packets

A synchronization packet (commonly known as the timing reference signal or TRS) occurs immediately before the first active sample on every line, and immediately after the last active sample (and before the start of the horizontal blank

Horizontal blank

Horizontal blanking interval refers to a part of the process of displaying images on a computer monitor or television screen via raster scanning. CRT screens display images by moving beams of electrons very quickly back and forth from the left to right side of the screen...

ing region). The synchronization packet consists of four 10-bit words, the first three words are always the same—0x3FF, 0, 0; the fourth consists of 3 flag bits, along with an error correcting code. As a result, there are 8 different synchronization packets possible.

In the HD-SDI and dual link interfaces, synchronization packets must occur simultaneously in both the Y and C datastreams. (Some delay between the two cables in a dual link interface is permissible; equipment which supports dual link is expected to buffer the leading link in order to allow the other link to catch up). In SD-SDI and enhanced definition interfaces, there is only one datastream, and thus only one synchronization packet at a time. Other than the issue of how many packets appear, their format is the same in all versions of the serial-digital interface.

The flags bits found in the fourth word (commonly known as the XYZ word) are known as H, F, and V. The H bit indicates the start of horizontal blank; and synchronization bits immediately preceding the horizontal blanking region must have H set to one. Such packets are commonly referred to as End of Active Video, or EAV packets. Likewise, the packet appearing immediately before the start of the active video has H set to 0; this is the Start of Active Video or SAV packet.

Likewise, the V bit is used to indicate the start of the vertical blanking region; an EAV packet with V=1 indicates the following line (lines are deemed to start at EAV) is part of the vertical interval, an EAV packet with V=0 indicates the following line is part of the active picture.

The F bit is used in interlaced and segmented-frame formats to indicate whether the line comes from the first or second field (or segment). In progressive scan

Progressive scan

Progressive scanning is a way of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence...

formats, the F bit is always set to zero.

Line counter and CRC

In the high definition serial digital interface (and in dual-link HD), additional check words are provided to increase the robustness of the interface. In these formats, the four samples immediately following the EAV packets (but not the SAV packets) contain a cyclic redundancy check

Cyclic redundancy check

A cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data...

field, and a line count indicator. The CRC field provides a CRC of the preceding line (CRCs are computed independently for the Y and C streams), and can be used to detect bit errors in the interface. The line count field indicates the line number of the current line.

The CRC and line counts are not provided in the SD and ED interfaces. Instead, a special ancillary data packet known as an EDH packet may be optionally used to provide a CRC check on the data.

Line and sample numbering

Each sample within a given datastream is assigned a unique line and sample number. In all formats, the first sample immediately following the SAV packet is assigned sample number 0; the next sample is sample 1; all the way up to the XYZ word in the following SAV packet. In SD interfaces, where there is only one datastream, the 0th sample is a Cb sample; the 1st sample a Y sample, the 2nd sample a Cr sample, and the third sample is the Y' sample; the pattern repeats from there. In HD interfaces, each datastream has its own sample numbering—so the 0th sample of the Y datastream is the Y sample, the next sample the Y' sample, etc. Likewise, the first sample in the C datastream is Cb, followed by Cr, followed by Cb again.

Lines are numbered sequentially, starting from 1, up to the number of lines per frame of the indicated format (typically 525, 625, 750, or 1125 (Sony HDVS

Sony HDVS

Sony HDVS was a range of high-definition video equipment developed in the 1980s to support an early analog high-definition television system thought to be the broadcast television systems that would be in use today...

)). Determination of line 1 is somewhat arbitrary; however it is unambiguously specified by the relevant standards. In 525-line systems, the first line of vertical blank is line 1, whereas in other interlaced systems (625 and 1125-line), the first line after the F bit transitions to zero is line 1.

Note that lines are deemed to start at EAV, whereas sample zero is the sample following SAV. This produces the somewhat confusing result that the first sample in a given line of 1080i video is sample number 1920 (the first EAV sample in that format), and the line ends at the following sample 1919 (the last active sample in that format). Note that this behavior differs somewhat from analog video interfaces, where the line transition is deemed to occur at the sync pulse, which occurs roughly halfway through the horizontal blanking region.

Link numbering

Link numbering is only an issue in dual-link interfaces. The first link (the primary link), is assigned a link number of 1, subsequent links are assigned increasing link numbers; so the second (secondary) link in a dual-link system is link 2. The link number of a given interface is indicated by a VPID packet located in the vertical ancillary data space.

Note that the data layout in dual link is designed so that the primary link can be fed into a single-link interface, and still produce usable (though somewhat degraded) video. The secondary link generally contains things like additional LSBs

Least significant bit

In computing, the least significant bit is the bit position in a binary integer giving the units value, that is, determining whether the number is even or odd. The lsb is sometimes referred to as the right-most bit, due to the convention in positional notation of writing less significant digits...

(in 12-bit formats), non-cosited samples in 4:4:4 sampled video (so that the primary link is still valid 4:2:2), and alpha or data channels. If the second link of a 1080P dual link configuration is absent, the first link still contains a valid 1080i signal.

In the case of 1080p60, 59.94, or 50 Hz video over a dual link; each link contains a valid 1080i signal at the same field rate. The first link contains the 1st, 3rd, and 5th lines of odd fields and the 2nd, 4th, 6th, etc. lines of even fields, and the second link contains the even lines on the odd fields, and the odd lines on the even fields. When the two links are combined, the result is a progressive-scan picture at the higher frame rate.

Ancillary data

Like SMPTE 259M

SMPTE 259M

, SMPTE 292M supports the SMPTE 291M standard for ancillary data. 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

Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

, closed captions, timecode, and other sorts of metadata

Metadata

The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...

. 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. Other than in their use in the header, the codes prohibited to video payload are also prohibited to ancillary data payload.

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

In dual link applications; ancillary data is mostly found on the primary link; the secondary link is to be used for ancillary data only if there is no room on the primary link. One exception to this rule is the VPID packet; both links must have a valid VPID packet present.

Embedded audio

Both the HD and SD serial interfaces provide for 16 channels of embedded audio. The two interfaces use different audio encapsulation methods - SD uses the SMPTE 272M standard, whereas HD uses the SMPTE 299M standard. In either case, an SDI signal may contain up to sixteen audio channels (8 pairs) embedded 48 kHz, 24-bit audio channels along with the video. Typically, 48 kHz, 24-bit (20-bit in SD) PCM audio is stored, in a manner directly compatible with the AES3 digital audio interface. These are placed in the (horizontal) blanking periods, when the SDI signal carries nothing useful, since the receiver generates its own blanking signals from the TRS.

In dual-link applications, 32 channels of audio are available, as each link may carry 16 channels.

EDH

As the standard definition interface carries no checksum, CRC, or other data integrity check, an EDH (Error Detection and Handling

Error Detection and Handling

In television technology, Error Detection and Handling protocol is an optional but commonly used addition to the Standard Definition-Serial Digital Interface standard...

) packet may be optionally placed in the vertical interval of the video signal. This packet includes CRC values for both the active picture, and the entire field (excluding those lines at which switching may occur, and which should contain no useful data); equipment can compute their own CRC and compare it with the received CRC in order to detect errors.

EDH is typically only used with the standard definition interface; the presence of CRC words in the HD interface make EDH packets unnecessary.

VPID

VPID (or video payload identifier) packets are increasingly used to describe the video format. 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. With the introduction of dual link interfaces, and segmented-frame standards, this is no longer possible; thus the VPID standard (defined by SMPTE 352M) provides a way to uniquely and unambiguously identify the format of the video payload.

Video payload and blanking

The active portion of the video signal is defined to be those samples which follow an SAV packet, and precede the next EAV packet; where the corresponding EAV and SAV packets have the V bit set to zero. It is in the active portion that the actual image information is stored.

Color encoding

Several color encodings are possible in the serial digital interface. The default (and most common case) is
10-bit linearly sampled video data encoded as 4:2:2 YCbCr

YCbCr

. (YCbCr is a digital representation of the YPbPr

YPbPr

' is a color space used in video electronics, in particular in reference to component video cables. is the analog version of the YCBCR color space; the two are numerically equivalent, but YPBPR is designed for use in analog systems whereas YCBCR is intended for digital video. cables are also...

colorspace). Samples of video are stored as described above. Data words correspond to signal levels of the respective video components, as follows:

The luminance (Y) channel is defined such that a signal level of 0 mV is assigned the codeword 64 (40 hex), and 700 millivolts (full scale) is assigned the codeword 940 (3AC hex) .
For the chroma channels, 0 mV is assigned the code word 512 (200 hex), -350mV is assigned a code word of 64 (40 hex), and +350mV is assigned a code word of 960 (3C0 hex).

Note that the scaling of the luma and chroma channels is not identical. The minimum and maximum of these ranges represent the preferred signal limits, though the video payload may venture outside these ranges (providing that the reserved code words of 0 - 3 and 1020 - 1023 are never used for video payload). In addition, the corresponding analog signal may have excursions further outside of this range.

Colorimetry

As YPbPr (and YCbCr) are both derived from the RGB colorspace, a means of converting is required. There are three colorimetries

Colorimetry

Colorimetry is "the science and technology used to quantify and describe physically the human color perception."It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color perception, most often the CIE 1931 XYZ color space...

typically used with digital video:

SD and ED applications typically use a colorimetry matrix specified in ITU-R Rec. 601.
Most HD, dual link, and 3Gb applications use a different matrix, specified in ITU-R Rec. 709
Rec. 709
ITU-R Recommendation BT.709, more commonly known by the abbreviations Rec. 709 or BT.709, standardizes the format of high-definition television, having 16:9 aspect ratio. The first edition of the standard was approved in 1990....

.
The 1035-line HD standards specified by SMPTE 260M (primarily used in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

and now largely considered obsolete), used a colorimetry matrix specified by SMPTE 240M. This colorimetry is nowadays rarely used, as the 1035-line formats have been superseded by 1080-line formats

Other color encodings

The dual-link and 3 Gbit/s interfaces additionally support other color encodings besides 4:2:2 YCbCr, namely:

4:2:2 and 4:4:4 YCbCr, with an optional alpha (used for chroma key
Chroma key
Chroma key compositing is a technique for compositing two images together. A color range in the top layer is made transparent, revealing another image behind. The chroma keying technique is commonly used in video production and post-production...

ing) or data (used for non-video payload) channel
4:4:4 RGB, also with an optional alpha or data channel
4:2:2 YCbCr, 4:4:4 YCbCr, and 4:4:4 RGB, with 12 bits of color information per sample, rather than 10. Note that the interface itself is still 10 bit; the additional 2 bits per channel are multiplexed into an additional 10-bit channel on the second link.

If an RGB encoding is used, the three primaries are all encoded in the same fashion as the Y channel; a value of 64 (40 hex) corresponds to 0mV, and 940 (3AC hex) corresponds to 700mV

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

Least significant bit

Vertical and horizontal blanking regions

For portions of the vertical and horizontal blanking regions which are not used for ancillary data, it is recommended that the luma samples be assigned the code word 64 (40 hex), and the chroma samples be assigned 512 (200 hex); both of which correspond to 0 mV. It is permissible to encode analog vertical interval information (such as vertical interval timecode

Vertical interval timecode

Vertical Interval TimeCode is a form of SMPTE timecode embedded as a pair of black-and-white bars in a video signal. These lines are typically inserted into the vertical blanking interval of the video signal...

or vertical interval test signals) without breaking the interface, but such usage is nonstandard (and ancillary data is the preferred means for transmitting metadata). Conversion of analog sync and burst signals into digital, however, is not recommended—and neither is necessary in the digital interface.

Supported video formats

The various versions of the serial digital interface support numerous video formats.

The 270 Mbit/s interface supports 525-line, interlaced video at a 59.94 Hz field rate (29.97 Hz frame rate), and 625-line, 50 Hz interlaced video. These formats are highly compatible with NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...

and PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...

-B/G/D/K/I systems respectively; and the terms NTSC and PAL are often (incorrectly) used to refer to these formats. (PAL is a composite color encoding scheme, and thus describes more than just the line-standard, while the serial digital interface— other than the obsolete 143 Mbit/s and 177 Mbit/s forms- is a component standard).

The 360 Mbit/s interface supports 525i and 625i widescreen. It can also be used to support 525p, if 4:2:0 sampling is used.

The various 540 Mbit/s interfaces support 525p and 625p formats.

The nominal 1.5 Gbit/s interfaces support most high-definition video
High-definition video
High-definition video or HD video refers to any video system of higher resolution than standard-definition video, and most commonly involves display resolutions of 1,280×720 pixels or 1,920×1,080 pixels...

formats. Supported formats include 1080/60i, 1080/59.94i, 1080/50i, 1080/30p, 1080/29.97p, 1080/25p, 1080/24p, 1080/23.98p, 720/60p, 720/59.94p, and 720/50p. In addition, there are several 1035i formats (an obsolete Japanese television standard), half-bandwidth 720p standards such as 720/24p (used in some film conversion applications, and unusual because it has an odd number of samples per line), and various 1080psf (progressive, segmented frame) formats. Progressive Segmented frames formats appear as interlace video but contain video which is progressively scanned. This is done to support analog monitors and televisions, many of which are incapable of locking to low field rates such as 30 Hz and 24 Hz.

The dual link HD interface supports 1080/60p, 1080/59.94p, and 1080/50p, as well as 4:4:4 encoding, greater color depth, RGB encoding, alpha channels, and nonstandard resolutions (often encountered in computer graphics or digital cinema
Digital cinema
Digital cinema refers to the use of digital technology to distribute and project motion pictures. A movie can be distributed via hard drives, optical disks or satellite and projected using a digital projector instead of a conventional film projector...

).

Related interfaces

In addition to the regular serial digital interface described here, there are several other similar interfaces which are similar to, or are contained within, a serial digital interface.

SDTI

There is an expanded specification called SDTI (Serial Data Transport Interface), which allows compressed (i.e. DV

DV is a format for the digital recording and playing back of digital video. The DV codec was launched in 1995 with joint efforts of leading producers of video camcorders....

, MPEG and others) video streams to be transported over an SDI line. This allows for multiple video streams in one cable or faster-than-realtime (2x, 4x,...) video transmission. A related standard, known as HD-SDTI, provides similar capability over an SMPTE 292M interface.

The SDTI interface is specified by SMPTE 305M. The HD-SDTI interface is specified by SMPTE 348M.

SMPTE 349M

The standard SMPTE 349M: Transport of Alternate Source Image Formats through SMPTE 292M, specifies a means to encapsulate non-standard and lower-bitrate video formats within an HD-SDI interface. 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.

G.703

The G.703 standard is another high-speed digital interface, originally designed for telephony.

Standards

Society of Motion Picture and Television Engineers: SMPTE 274M-2005: Image Sample Structure, Digital Representation and Digital Timing Reference Sequences for Multiple Picture Rates
Society of Motion Picture and Television Engineers: SMPTE 292M-1998: Bit-Serial Digital Interface for High Definition Television
Society of Motion Picture and Television Engineers: SMPTE 291M-1998: Ancillary Data Packet and Space Formatting
Society of Motion Picture and Television Engineers: SMPTE 372M-2002: Dual Link 292M Interface for 1920 x 1080 Picture Raster

External links

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