Digital Video Signal According to ITU-BT.R.601 (CCIR 601) - Digital Video and Audio Broadcasting Technology - page 83

with a C B value or a C R value and there are twice as many Y values as
there are C B or C R values. This is called a 4:2:2 resolution, compared with
the resolution immediately after the matrixing, which was the same for all
components, namely 4:4:4.

. . . . .

. . . . .

1234

TRS = Timing
Reference Sequence
4 code words
(SAV or EAV
= Start of active
video or end
of active video)

Fig. 4.3. SAV and EAV code words in the ITU-BT.R601 signal

This digital signal can be present in parallel form at a 25 pin sub-D con-
nector or serially at a 75 Ohm BNC socket. The serial interface is called
SDI which stands for serial digital interface and has become the most
widely used interface because a conventional 75-Ohm BNC cable can be
used.
Within the data stream, the start and the end of the active video signal is
marked by special code words called SAV (start of active video) and EAV
(end of active video), naturally enough (Fig. 4.2.). Between EAV and
SAV, there is the horizontal blanking interval which does not contain any
information related to the video signal, i.e. the digital signal does not con-
tain the sync pulse. In the horizontal blanking interval, supplementary in-
formation can be transmitted such as, e.g. audio signals (embedded audio).
The SAV and EAV code words (Fig. 4.3.) consist of four 8 or 10 bit
code words each. SAV and EAV begins with one code word in which all
bits are set to one, followed by two words in which all bits are set to zero.
The fourth code word contains information about the respective field or the
vertical blanking interval, respectively. This fourth code word is used for
detecting the start of a frame, field and active picture area in the vertical