Letterbox (clip, int top, int bottom, [int left], [int right], int
"color")
Letterbox simply blackens out the top top and the bottom bottom,
and optionally left and right side of each frame.
This has a couple of uses: one, it can eliminate stray
video noise from the existing black bands in an image that's already letterboxed;
two, it can eliminate the garbage lines that often appear at the bottom of the
frame in captures from VHS tape.
The functionality of Letterbox can be duplicated with a combination
of Crop and AddBorders, but
Letterbox is faster and
easier.
Generally, it's better to crop this stuff off using Crop
or CropBottom
than to hide it with Letterbox. However, in some cases, particularly
if you're compressing to MPEG, it's better to use Letterbox
because
it lets you keep a standard frame size like 352x288 or 320x240. Some MPEG players
get confused when the source video has a strange frame size.
The color parameter is optional, default=0 <black>, and is specified as an RGB value regardless of whether the clip format is RGB or YUV based. See here for more information on specifying colors.
Another use could also be to clear out overscan areas in VCD or SVCD encodings.
$Date: 2008/06/06 11:37:04 $