Letterbox

Fills the top and bottom rows of each frame, and optionally the left and right columns, with black or color. This has several common uses:

• Adjust the aspect ratio (letterboxing's traditional purpose)
• Black out video noise from the existing black bands in an image that's already letterboxed
• Black out the video noise at the bottom of the frame in VHS tape sources.
• Black out overscan areas in VCD or SVCD sources.
• Create a quick rectangular mask for other filters – a so-called "garbage matte"

See also: AddBorders, which increases frame size. Letterbox does not change frame size.

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 video noise off than to black it out; many older lossy compression algorithms don't deal well with solid-color borders, unless the border happens to fall on a macroblock boundary (16 pixels for MPEG). However, in some cases, particularly for certain hardware players, it's better to use Letterbox because it lets you keep a standard frame size.

Syntax and Parameters

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

int  top, bottom = (required)

Number of top and bottom rows to blank out.

\::*For YV12 sources, top and bottom must be mod2 (divisible by 2).

int  x1, x2 = 0

Number of left (x1) and right (x2) columns to blank out.

• For YUY2, YV16 and YV12 sources, left and right must be mod2 (divisible by 2).
• For YV411 sources, left and right must be mod4 (divisible by 4).

int  color = (black)

Fill color; specified as an RGB value. See this page for more information on specifying colors.

• For YUV clips, colors are converted from full-range (0–255) to tv-range (16–235).

Changes

v2.07	Added color option.
v2.06	Added optional left and right parameters (x1 and x2).