See Figure 15.2, on page 144.

SMPTE ST 292, Bit-Serial Digital Interface for High-Definition Television Systems.

interfaces are indicated in the margin. This interface is standardized for Y’CBCR, subsampled 4:2:2. Dual-link HD-SDI can be used to convey R’G’B’A, 4:4:4:4.

HD-SDI accommodates 1080i25 and 1080p25 variants that might find use in Europe. This is accomplished by placing the 1920× 1080 image array in

a scanning system having 25 Hz rate. STL is altered from the 30 Hz standard to form an 1125/25 raster.

The standard HD analog interfaces use trilevel sync, instead of the bilevel sync that is used for analog SD. Figure 38.3 above shows the scan-line waveform, including trilevel sync, for 1080i30 HD.

The HD-SDI interface is standardized in SMPTE ST 292. Fiber-optic interfaces for digital HD are also specified in SMPTE ST 292.

SDI and HD-SDI sync, TRS, and ancillary data

Along with picture information, a streaming interface needs to convey information about which time instants – or which digital samples – are associated with the start of each frame and the start of each line. In digital video, this information is conveyed by timing reference signals (TRS) that I will explain in this chapter.

SDI has the capacity to transmit ancillary (ANC) data. The serial data transport interface (SDTI) resembles SDI,

I use the subscript h to denote a hexadecimal (base 16) integer. Sample values in this chapter are expressed in 10 bits.

The V and H bits are asserted during the corresponding blanking intervals. The F bit denotes field, not frame.

but has no uncompressed active video – instead, the full data capacity of the link is dedicated to carrying ANC packets. Compressed digital video can be conveyed in these packets. SDTI will be described on page 441.

The IEEE 1394/DV interface, described on page 167, and the DVB-ASI interface, to be described on

page 443, have no ancillary data and do not use TRS. Standard serial interfaces transmit 10-bit samples; a transmitter must present all 10 bits at the interface

(even if the two LSBs are zero).

TRS and ANC sequences are introduced by 10-bit codewords 0 and 3FFh. Stemming from legacy parallel interfaces such as SMPTE RP 125 and EBU Tech. 3246, a receiver must ignore the two LSBs in identifying TRS and ANC. Apart from their use to delimit TRS and ANC, codewords 0, 1, 2, 3, and 3FCh, 3FDh, 3FEh, and 3FFh are prohibited from digital video data.

TRS in 4:2:2 SD-SDI

In Component digital SD interface (BT.601), on page 430, I explained that 4:2:2 samples are multi-

plexed in the sequence {CB, Y0’, CR, Y1’} onto the SDI. BT.601 defines the abstract signal coding parameters; BT.656 defines the interface.

Active luma samples are numbered from zero to SAL-1; active chroma samples are numbered from zero to (SAL/2)-1. The interface transmits two words for each luma sample clock: Even-numbered words convey chroma samples; odd-numbered words convey luma samples. The sample structure aligns with 0H: If analog sync were digitized, a particular digitized luma sample would precisely reflect the 50% value of sync.

In 4:2:2 video, a four-word TRS sequence immediately precedes active video, indicating start of active video (SAV). SAV is followed by CB sample zero. Immediately following the last active sample of the line is another four-word TRS sequence, end of active video (EAV). The TRS sequence comprises a word of all ones (codeword 3FFh), a word of all zeros, another word of all zeros, and finally a word including flag bits F (Field), V (Vertical), H (Horizontal), P3, P2, P1, and P0 (Parity). SAV is indicated by H=0; EAV has H=1.

Table 38.3 shows the elements of TRS.

In BT.601-4 (1994) and in SMPTE RP 125-1992, in 480i systems, an SAV with V=0 could occur prior to the first active (picture) line – as early as line 10 or line 273. To be compatible with legacy equipment, do not rely upon the 1-to-0 transition of V.

The F and V bits change state in the EAV prior to the start of the associated line; rather than calling it EAV, you might call it start of horizontal interval. In interlaced systems, F is asserted during the second field. In 480i systems, F changes at lines 4 and 266; in other scanning systems, including 576i and HD, F changes state at line 1. In progressive systems, F is always zero (except in 483p59.94, where F encodes frame parity.)

The vertical blanking (V) bit is zero in every line that is defined by the associated scanning standard to contain active (picture) video; it is asserted elsewhere – that is, in the vertical interval.

The F, V, and H bits are protected by parity bits P3, P2, P1, and P0, formed as indicated in Table 38.4 by an exclusive-or across two or three of F, V, and H.

SMPTE ST 348, High Data-Rate

Serial Data Transport Interface

(HD-SDTI).

SMPTE standards are inconsistent in their numbering of words outside the active region. EAV functions as the start of a digital line with regard to state changes to the F and V bits, so I number words from 0 at EAV. In this scheme, SAV starts at word STL-SAL-4. Another reason for numbering EAV as word 0 is that the proposed SMPTE standard for HD-SDTI anticipates a scheme to advance the timing of SAV codes. Word and sample numbering is strictly notational: Neither word nor sample numbers appear at the interface.

The horizontal blanking interval at the interface, from EAV to SAV, can contain ancillary data (HANC). In each active (picture) line, the interval from SAV to EAV contains active video. Outside the active picture lines, the interval between SAV and EAV can be used for ancillary data (VANC) packets. If a line outside the active picture is not carrying VANC, and the line isn’t associated with analog sync elements, the interval from SAV to EAV can carry a digitized ancillary signal coded like active video. Intervals not used for EAV, SAV, active video, digitized ancillary signals, or ancillary (ANC) data are filled by alternating codes {chroma 200h, luma 40h}, which, in active picture, would represent blanking.

TRS in HD-SDI

HD-SDI is similar to 4:2:2 SD SDI; however, the single link carries two logical streams, one carrying chroma, the other carrying luma. Each stream has TRS sequences; independent ANC packets can be carried in each stream. The two streams are word multiplexed; the multiplexed stream is serialized and scrambled. Four words indicated in Table 38.5 at the top of the facing page are appended to each EAV. Each bit 9 is the complement of bit 8. Words 4 and 5 convey line number (LN0, LN1). Words 6 and 7 provide CRC protection for the stream’s active video. Each stream has a CRC generator that implements a characteristic function x18 +x5 +x4 + 1. Each generator is reset to zero immediately after SAV, and accumulates words up to and including LN1.