Ah, with you now.
Getting from the DVD to clips is done by playing the disc through the VLC application, from which I can then hit a record button to record the clips I want. Can't tell you the file extension yet, as my laptop is at home and I'm at work.
I have tried cropping the clips via VLC and then recording the cropped version, but when playing the clip afterwards the ratio has gone back to its normal setting. Maybe I'm missing something.
Will come back to you tomorrow with the file extension details.