Letterbox

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Letterbox(clip clip, int top, int bottom [, int x1] [, int x2] [, int color])

Letterbox simply blocks out the upper top and lower bottom scanlines of each frame, and / or optionally blocking out the left (x1) and right (x2) portions for HDTV letterboxing, and using black by default or specifying an optional color. 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.

Another use could also be to clear out overscan areas in VCD or SVCD encodings.

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