Recently I needed to create video demo for one for my developed application, and I needed to remove some unwanted portion from video. In windows there are plenty of application for doing so, but now I use Ubuntu operating system. I search for video editing software for Ubuntu and I found one great application.
Its command line tool and its name is ffmpeg.
It can cut video clip from large video, if you want to crop video it support this as well and it support wide range of video codec.
To install this tool type following command on terminal
sudo apt-get install ffmpeg
Following command will clip video and put it in output file
ffmpeg -i movie.avi -ss 00:51:42 -t 00:03:30 clip.avi
To crop video , use following commands
ffmpeg -i input.avi -croptop 50 output.avi
ffmpeg -i input.avi -cropbottom 50 output.avi
To change aspect ration use following command
ffmpeg -i input.avi -aspect 16:9 output.avi
Here is documentation for ffmpeg tool it you need some more options.