OG-UDC 3G-SDI Up, Down, Cross-Converter v1.0 10 www.aja.com
Selection Description
• Letterbox – Image is reduced with black top and bottom added to image area,
with the aspect ratio preserved.
• Crop (default) – Image is cropped to fit new screen size.
• Anamorphic – HD image is converted to full-screen SD with a 16x9 aspect ratio
(anamorphic).
• 14:9 – Image is reduced slightly with aspect ratio preserved. Black is added top
and bottom, and the left and right sides are cropped.
• Auto AFD – Automatically selects the best Downconvert mode based on the
input video's Active Format Description (AFD) code.
Active Format Description (AFD) codes are carried in the vertical ancillary
(VANC) portion of HD SDI video signals, specified in SMPTE 2016 as follows:
“AFD information is intended to guide DTV receivers and/or intermediate
professional video equipment regarding the display of video of one aspect
ratio on a display of another aspect ratio.”
In the OG-UDC Downconverter, the AFD code on the video input can be used
to guide the Downconverter in choosing which mode to use to best display
the important content of the16:9 HD input video on the 4:3 SD output. For
example, if the input AFD code is 10 (Full Frame), it means that the input video
has important picture information throughout the full 16:9 frame, so the
Downconverter should use Letterbox mode to be sure none of the content
is cropped off. An AFD code of 9 (Pillarbox) says that the input video only has
content within the center 4:3 area of the picture (usually because it originally
came from an Upconverted SD signal) so the Downconverter Crop mode
would be the best choice. There are 16 possible HD AFD codes, of which 8 are
in common use. The OG-UDC does not process or use SD AFD codes.
SD Aspect Ratio Convert
This mode selects the type of SD-to-SD Aspect Ratio Conversion (ARC) performed
on an incoming selected SD source. This mode is in effect only when the input
and output are both SD (525i or 625i). (In Europe 16:9 anamorphic video is also
known as “wide screen” video.)