Ancillary data is data that has been added to given data and uses the same form of transport. Common examples are cover art images for

media file This is a list of file formats used by computers, organized by type. Filename extension it is usually noted in parentheses if they differ from the file format name or abbreviation. Many operating systems do not limit filenames to one extension s ...

s or streams, or digital data added to

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmi ...

television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertisin ...

broadcasts.

Television

Ancillary data (commonly abbreviated as ANC data), in the context of

systems, refers to a means which by non-video information (such as

audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound * Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum * Digital audio, representation of sou ...

, other forms of

essence Essence ( la, essentia) is a polysemic term, used in philosophy and theology as a designation for the property or set of properties that make an entity or substance what it fundamentally is, and which it has by necessity, and without which it ...

, and metadata) may be ''embedded'' within the serial digital interface. Ancillary data is standardized by

SMPTE The Society of Motion Picture and Television Engineers (SMPTE) (, rarely ), founded in 1916 as the Society of Motion Picture Engineers or SMPE, is a global professional association of engineers, technologists, and executives working in the m ...

as ''SMPTE 291M: Ancillary Data Packet and Space Formatting''. Ancillary data can be located in non-picture portions of horizontal

scan line A scan line (also scanline) is one line, or row, in a raster scanning pattern, such as a line of video on a cathode ray tube (CRT) display of a television set or computer monitor. On CRT screens the horizontal scan lines are visually discernible ...

s. This is known as horizontal ancillary data (HANC). Ancillary data can also be located in non-picture regions of the

frame A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent. Frame and FRAME may also refer to: Physical objects In building construction *Framing (con ...

, This is known as vertical ancillary data (VANC).

Technical details

Location

Ancillary data packets may be located anywhere within a serial digital data stream, with the following exceptions: * They should not be located in the lines identified as a ''switch point'' (which may be lost when switching sources). * They should not be located in the active picture area. * They may not cross the TRS (timing reference signal) packets. Ancillary data packets are commonly divided into two types, depending on where they are located—specific packet types are often constrained to be in one location or another. * Ancillary packets located in the

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 across the screen. Once the bea ...

ing region (after EAV but before SAV), regardless of line, are known as horizontal ancillary data, or HANC. HANC is commonly used for higher-bandwidth data, and/or for things that need to be synchronized to a particular line; the most common type of HANC is

embedded audio Embedded or embedding (alternatively imbedded or imbedding) may refer to: Science * Embedding, in mathematics, one instance of some mathematical object contained within another instance ** Graph embedding * Embedded generation, a distributed ge ...

. * Ancillary packets located in the

vertical blank In a raster scan display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final visible line of a frame or field and the beginning of the first visible line of the next fram ...

ing region, and after SAV but before EAV, are known as vertical ancillary data, or VANC. VANC is commonly used for low-bandwidth data, or for things that only need be updated on a per-field or per-frame rate. Closed caption data and VPID are generally stored as VANC. Note that ANC packets which lie in the dataspace which is in both the horizontal ''and'' vertical intervals, is considered to be HANC and not VANC. VANC packets should be inserted in this manner: * (SMPTE 334M section 3): VANC data packets can appear anywhere between the SAV and EAV TRS packets in any line from the second line after the line specified for switching to the last line preceding active video, inclusive. Given the spec for switch points (set RP168 figure 2), the first allowed lines are 12 and 275 (for 525-line/59.94 Hz systems) or 8 and 321 (for 625-line/50 Hz systems). This conflicts with SMPTE 125M, and does not address requirements for carrying DVITC (Digital Vertical Interval TimeCode) and video index packets. * (SMPTE 125M section 3.6.2): VANC should appear only in lines 1-13, 15-19, 264-276, and 278-282, with lines 14 and 277 reserved for DVITC and video index data. This conflicts with SMPTE 334M, and does not address 625-line/50 Hz systems.

Packet format

All ANC packets must start with a start sequence; for component interfaces (the only kind of serial digital interface in widespread use today), the start sequence is 0x000 0x3FF 0x3FF. This sequence is otherwise illegal in the serial digital interface. (In the obsolete composite versions of SDI, the ANC start sequence is a single word, 0x3FC). Three words immediately follow the start sequence in the header. The first word after the start sequence is the Data Identifier or DID, followed by either a 'Secondary Data Identifier (SDID) ''or'' a Data Block Number (DBN), followed by a Data Count (DC). After the Data Count word are 0 - 255 (inclusive) User Data Words (UDW), followed by a Checksum (CS) word.

= DID

= The Data Identifier word (along with the SDID, if used), indicates the type of ancillary data that the packet corresponds to. Data identifiers range from 1 to 255 (FF hex), with 0 being reserved. As the serial digital interface is a 10-bit format, the DID word is encoded as follows: * Bits 0-7 (bit 0 being the LSB), are the raw DID value. * Bit 8 is the

even parity A parity bit, or check bit, is a bit added to a string of binary code. Parity bits are a simple form of error detecting code. Parity bits are generally applied to the smallest units of a communication protocol, typically 8-bit octets (bytes), ...

bit of bits 0-7. * Bit 9 is the inverse of bit 8. Thus, a DID of 0x61 (01100001) would be encoded as 0x161 (0101100001), whereas a DID of 0x63 (01100011) would be encoded as 0x263 (1001100011). Note that this encoding scheme ensures that the reserved values in the serial digital interface (0-3 and 1020-1023) are never used. If the DID is equal to 128 (0x80) or greater, then the packet is a Type 1 packet, and the DID is sufficient to identify the packet type, and the following word is a Data Block Number. If the DID is less than 128, it is a Type 2 packet, and the following words is the Secondary Data Identifier; the DID and SDID together identify the packet type.

= SDID

= The SDID is only valid if the DID is less than 0x80. The SDID is nominally an 8-bit value, ranging from 0 to 255. It is encoded in the same fashion as the DID. DID/SDID words of 161 101 (hex) correspond to a DID of 61 hex, and a SDID of 1 (once the two high bits are removed); these values would indicate that the packet type is defined by ''SMPTE 334M'', and contains DTV closed captions data.

=DBN

= The DBN is only valid if the DID is 80 hex or greater. It is (optionally) used to identify multiple packets of the same type within a field; each subsequent packet of the indicated type has a DBN which is one higher than the previous packet, wrapping around as necessary. The DBN is an 8-bit value, encoded in the same fashion as the SDID.

=DC

= The Data Count word is an 8-bit value, encoded in the same fashion as the DID, which indicates how many user data words are to follow. It can range from 0 to 255.

=UDW

= User data words are the "payload" present in the ANC packet. They are defined according to the packet type, SMPTE 291M does not define their use or impose any restrictions on the values which may be present in the UDW space. The only restriction is that the reserved values in the serial digital interface (0-3 and 1020-1023) may not be included in the UDW. Many ANC formats, though not all, are essentially 8-bit formats, and encode data in the same manner that the header words are encoded.

Example

SMPTE 352M (Video Payload ID) defines four UDW:

=Checksum

= The last word in an ANC packet is the Checksum word. It is computed by computing the sum (modulo 512) of bits 0-8 (not bit 9), of all the other words in the ANC packet, excluding the packet start sequence. Bit 9 of the checksum word is then defined as the inverse of bit 8. Note that the checksum word does not contain a parity bit; instead, the parity bits of other words are included in the checksum calculations.

Usage

Embedded audio

Embedded audio Embedded or embedding (alternatively imbedded or imbedding) may refer to: Science * Embedding, in mathematics, one instance of some mathematical object contained within another instance ** Graph embedding * Embedded generation, a distributed ge ...

is audio payload which is (typically) the soundtrack (music, dialogue, and sound effects) for the video program. Two standards, ''SMPTE 272M'' (for SD) and ''SMPTE 299M'' (for HD and 3G) define how audio is embedded into the ancillary space. The SD and HD standards provide for up to 16 channels of PCM audio, while 3G allows up to 32 channels, typically encoded in the

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format. In HD, the embedded audio data packets are carried in the HANC space of Cb/Cr (chroma) parallel data stream. In addition, both standards define audio control packets. The audio control packets are carried in the HANC space of the Y (luminance) parallel data steam and are inserted once per field at the second video line past the switching point (see SMPTE RP168 for switching points of various video standards). The audio control packet contains audio-related metadata, such as its timing relative to video, which channels are present, etc. Embedded audio packets are Type 1 packets.

EDH

EDH packets are used for error detection in standard definition interfaces (they are not necessary in HD interfaces, as the HD-SDI interface includes CRC checkwords built in).

External links

: ''SMPTE 291M-1998: Ancillary Data Packet and Space Formatting'' *

: ''ANSI/SMPTE 125M-1995: Component Video Signal 4:2:2; Bit-Parallel Digital Interface'' *

: ''ANSI/SMPTE 334M-1995: Vertical Ancillary Data Mapping for Bit-Serial Interface'' *

: ''RP168-2002: Definition of Vertical Interval Switching Point for Synchronous Video Switching'' *

: ''SMPTE 299-1:2010: 24-Bit Digital Audio Format for SMPTE 292 Bit-Serial Interface'' *

: ''SMPTE 299-2:2010: Extension of the 24-Bit Digital Audio Format to 32 Channels for 3 Gb/s Bit-Serial Interfaces'' *

:
Data Identification Word Assignments for Registered DIDs
{{SMPTE standards Film and video technology Serial digital interface SMPTE standards