by Steffen Klupsch <[email protected]>
Boundary Conditions (valid for transcode-0.5.0 and later):
- 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
- Clipping of the input image.
- Changing the aspect ratio of the 1) output.
- Clipping of the 2) output.
Used Options:
- 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
- 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'
- 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.
Examples on Usage:
- 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:
'-j 32,0 -B 4,0 -Y 24,0'
Final image size: 720x336 Pixel
- 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:
'-j 32,8 -X 0,2 -B 3,0 -Y 24,0'
Final image size: 768x368 Pixel
- Using the fast -X resizing, expanding the image width,
but removing 3% of the image at the left and the right border:
'-j 64,24 -X 0,7'
Final image size: 896x448 Pixel
- Using the slower -Z resizing, expanding the image width to PAL
resolution:
'-j 68,0 -Z 768x360'
Final image size: 768x360 Pixel
- Using the slower -Z resizing, 800 Pixel image width:
'-j 66,0 -Z 800x368'
Final image size: 800x368 Pixel
- Using the slower -Z resizing, expanding the image width:
'-j 64,0 -Z 960x448'
Final image size: 960x448 Pixel
- 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:
'-B 4,0'
Final image size: 720x448 Pixel
- Using the fast -X resizing, expanding the image width,
but removing 3% of the image at the left and the right border:
'-j 0,24 -X 0,7'
Final image size: 896x576 Pixel
- Using the slower -Z resizing, expanding the image width
to PAL resolution:
'-Z 768x472'
Final image size: 768x472 Pixel
- Using the slower -Z resizing, 800 Pixel image width:
'-Z 800x480'
Final image size: 800x480 Pixel
- Using the slower -Z resizing, expanding the image width:
'-Z 960x576'
Final image size: 960x576 Pixel
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