How to crop letterbox video clips for easier scene change detection

Top  Previous 

In letterbox movies, almost half the picture consists of two black bars. As Sub Machine's Scene Spy finds scene changes by comparing frames and spotting a certain amount of differences, a letterbox clip where half the picture never changes offers a special challenge. You may actually spot most letterbox clip scene changes by giving setup/video configuration/scene change/cut a very high value, but there's a much better solution: Removing the pesky bars.

 

1) As always before scene change detection, calibrate the clip. We are going to remove the superimposed time code as well, so make damn sure that the running time code is correct start through end before you eliminate your only way of checking it. Once the clip is calibrated, make a backup of the [clipname].txt file in your videoclips folder. *

 

2) In VirtualDub, select Video/filters/add/null transform/cropping:

 

 

FWletterbox

Letterbox clip loaded

 

 

3) Now increase the values of the four X and Y offset boxes until the bars are gone. If you use the same number in all four boxes, the 4:3 ratio is maintained. If you only want to remove the bars, that's okay. The program will find the scene changes no matter how the picture looks.

 

warning Please notice that the number used must be divisible by 4!

 

FW4-3.

Ready for cropping to 4:3 format

 

4) Hit the OK button and start the usual conversion procedure (file/save as [newfilename]avi.). Give the clip the same name as the *.txt file you just backed up.

 

5) After running the scene change detection, you may use the original letterbox clip again. Just rename the *.txt file once more, giving it back its original name.

 


* If  you are absolutely sure that no frames have been dropped, you may skip the calibration bit and do it later.

 


warning This is strictly off-topic, but try looking at the two pictures above to see how much you are actually missing when watching a cropped feature movie on tv!