Common examples are cover art images for media files or streams, or digital data added to radio or television broadcasts.
Ancillary data (commonly abbreviated as ANC data), in the context of television systems, refers to a means which by non-video information (such as audio, other forms of essence, and metadata) may be embedded within the serial digital interface.
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.
(In the obsolete composite versions of SDI, the ANC start sequence is a single word, 0x3FC).
Note that this encoding scheme ensures that the reserved values in the serial digital interface (0-3 and 1020-1023) are never used.
User data words are the "payload" present in the ANC packet.
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.
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.