Digital sync, TRS, ancillary data, and interface

This chapter explains the timing reference signals (TRS), ancillary (ANC) data in digital video. It outlines the Serial digital interface (SDI) that has the capacity to transmit ancillary data. The serial data transport interface (SDTI) resembles SDI, but has no uncompressed active video—instead, the full data capacity of the link is dedicated to carrying ANC packets. Compressed digital video—such as DV25 or DV50—can be conveyed in these ANC packets. TRS and ANC sequences are introduced by 10-bit codewords 0 and 3FFh. For compatibility with legacy parallel interfaces such as SMPTE RP 125 and EBU Tech.3246, a receiver must ignore the two LSBs in identifying TRS and ANC. In 4:2:2 SDTV, and in HDTV, ancillary data is permitted immediately after any EAV (FIANC), or immediately after SAV (VANC) on a line containing neither active picture nor digitized ancillary data. The SDI uses scrambled coding, where the data stream is serialized, then passed through a shift register arrangement with exclusive-or taps implementing a characteristic function x 9 + x 4 + 1.