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ARC130S SECTION
4
ARC130S 060801 Version 1 Issue 1
4.30
APPENDIX –
Video Index and Enhanced Line 23
The ARC130S can read incoming video index signals and output it’s own video index signal. Video index is a
signal embedded in the D1 output stream that can be used to convey aspect ratio information. The basic
version of video index is described in SMPTE document RP186. An enhanced version of video index
incorporating more aspect ratio information has been introduced in the United Kingdom for control of MPEG
encoders. The ARC130S supports both forms of video index and, they are referred to as SMPTE186 and AFD
Spec’ version throughout. (AFD is Active Format Descriptor). The serial data format of the video index is
described in SMPTE document SMPTE125M-1995.
In the United Kingdom, a modified version of line 23 signalling which allows the embedding of the same
information as that in AFD spec Video Index signals has been defined. The ARC130S supports this AFD spec
version of line 23 at both it’s input and output. The new line 23 will be referred to as L23 AFD and the previous
version of line 23 as L23 ETSI throughout.
BACKGROUND INFORMATION ON VIDEO INDEX
The original SMPTE RP186 video index scheme includes in the very first data byte (Class 1.1 data Octet 1) a
scanning system field. This can signal either 4:3 or 16:9 using the bottom 3 bits of the data byte as shown
below.
Octet Value
Meaning
B2
B1
B0
0
no information
0
0
0
1
525/59.94 4:3
0
0
1
2
625/50 4:3
0
1
0
3
Reserved
0
1
1
4
Reserved
1
0
0
5
525/59.94 16:9
1
0
1
6
625/50 16:9
1
1
0
7-255
Reserved
1
1
1
Within Europe an extension to this data byte has been defined and is known as the ARDSPEC version. AFD
being Active Format Descriptor. This retains the meaning of the bottom 3 bits of the data byte as 4:3 or 16:9
but in addition, it defines the meanings of the next 3 bits as follows.
Active format
Intended aspect ratio of active region
B5
B4
B3
0
Active region is same as coded frame
0
0
0
1
4:3
0
0
1
2
16:9
0
1
0
3
14:9
0
1
1
4
Reserved for future use
1
0
0
5
4:3 with shoot-and-protect 14:9 centre
1
0
1
6
16:9 with shoot-and-protect 14:9 centre
1
1
0
7
16:9 with shoot-and-protect 4:3 centre
1
1
1
The enhanced version of Line 23 (L23 AFD) basically embeds the sane information in the line 23 data. i.e. the
Scanning system and AFD fields. In addition, it provides four User bits.