Product specifications
Up/Down/Cross (UDX) Conversion
190
Video Format
In SDI video, the ancillary data that defines the video format is called AFD, or Active Format
Description. AFD is defined as a 4-bit number; there are 16 possible values. However, many of
these are reserved and are not used. The most common AFD values include:
• SD, AFD=9: 4:3 image
• SD, AFD=10: 16:9 image, letterboxed (black bars at top and bottom)
• HD, AFD=10: 16:9 image
• HD, AFD=9: 4:3 image, pillarboxed (black bars on left and right sides)
The AFD code is used to describe the video format before and after conversion. One of the
primary purposes of using AFD to describe the image format is so that processing and display
equipment can make intelligent choices. For example, if the starting image is a pillarboxed 4:3
image (AFD=9):
When down converting this image to SD, an intelligent approach is to simply remove the black
bars from the 2 sides. If the black bars are removed, then the resultant image is now a full-screen
4:3 image, and would get stamped with an AFD code of 9.
The main goal is to avoid letterboxing an image that is already pillarboxed (or vice versa). When
this happens, you get black bars on both the top and bottom, and the left and right sides, and the
active picture is smaller than it needs to be: