Transcode_Wiki: Command Examples/Clipping And Resizing Guide

Boundary Conditions

Maximum image size is 1024x768
The video frame operations ordering is fixed: -j -I -X -B -Z -Y -r -z -l -k -K -G -C (executed from left to right)
Shrinking the image with '-B' is not possible if the image width/height is not a multiple of 32.
Expanding the image with '-X' is not possible if the image width/height is not a multiple of 32.
The final frame width/height should be a multiple of 8. (to avoid encoding problems with some divx codecs)

Reducing the video height/width by 2,4,8 Option '-r factor' can be used to shrink the video image by a constant factor, this factor can be 2,4 or 8.
Clipping and changing the aspect ratio transcode uses 3 steps to produce the input image for the export modules
1. Clipping of the input image.
2. Changing the aspect ratio of the 1) output.
3. Clipping of the 2) output.

Used Options

1

The first clipping is defined by the option -j top[,left[,bottom[,right]]] if you don't specify all parameters, they will be assumed to be symmetric to the others.

 -j 80 is expanded to -j 80,0,80,0 (top,left,bottom,right)
 -j 80,8 is expanded to -j 80,8,80,8
 -j 80,8,10 is expanded to -j 80,8,10,8

2

Changing the aspect ration can be done in 3 ways:

(fast) shrinking the image with option -B n[,m]
(fast) expanding the image with option -X n,[m]
(high quality) resizing with option -Z wxh

3

The 2nd clipping is defined by the option -Y top[,left[,bottom[,right]]] if you don't specify all parameters, they will be assumed to be symmetric to the others.

Usage Examples

1

Input data 16:9 widescreen DVD data, output data should have 4:3 aspect ratio without black border. Analyze the input data, we assume a black border at the top and bottom of 66 pixel in a 720x576 pixel frame.

Using the fast resizing option -B, shrinking the height to reach a correct aspect ratio. Final image size: 720x336 Pixel.

 -j 32,0 -B 4,0 -Y 24,0

Using the fast resizing options -X and -B, removing 1% at the left&right border, expanding the image width to PAL resolution, and shrinking the height to reach a correct aspect ratio. Final image size: 768x368 Pixel.

 -j 32,8 -X 0,2 -B 3,0 -Y 24,0

Using the fast -X resizing, expanding the image width, but removing 3% of the image at the left and the right border. Final image size: 896x448 Pixel.

 -j 64,24 -X 0,7

Using the slower -Z resizing, expanding the image width to PAL resolution. Final image size: 768x360 Pixel.

 -j 68,0 -Z 768x360

Using the slower -Z resizing, 800 Pixel image width. Final image size: 800x368 Pixel.

 -j 66,0 -Z 800x368

Using the slower -Z resizing, expanding the image width. Final image size: 960x448 Pixel.

 -j 64,0 -Z 960x448

2

Input data '16:9' DVD data without black borders, output data should have 4:3 aspect ratio.

Using the fast resizing option -B, shrinking the height to reach correct aspect ratio. Final image size: 720x448 Pixel.

 -B 4,0

Using the fast -X resizing, expanding the image width, but removing 3% of the image at the left and the right border. Final image size: 896x576 Pixel.

 -j 0,24 -X 0,7

Using the slower -Z resizing, expanding the image width to PAL resolution. Final image size: 768x472 Pixel.

 -Z 768x472

Using the slower -Z resizing, 800 Pixel image width. Final image size: 800x480 Pixel.

 -Z 800x480

Using the slower -Z resizing, expanding the image width. Final image size: 960x576 Pixel.

 -Z 960x576