Ubuntu – How to crop a video clip

1. How to quickly mark a segment to delete:

1. Make sure the video track is selected.
2. Press X to switch to the Cut (Razor) Tool
3. Click once in the timeline at the start point
4. Click once at the end point

5. Press S again to switch back to selection mode

   

2. Use xdotool to automate delete/remove space with a single keyboard shortcut

1. xdotool allows automation of keyboard and mouse clicks/movements; install it with sudo apt-get install xdotool

2. Copy and paste the below to an sh file, say kdenlive_cut.sh in your home directory:

   #!/bin/bash
   
   DELAY=0.5  # delay in seconds between each action
   xdotool search --limit 1 -name Kdenlive > nul  # activate only if kdenlive running
   if [ $? -eq 0 ]
   then xdotool click 1 && sleep $DELAY \       # left-click
      && xdotool key Delete && sleep $DELAY \  # DEL
      && xdotool click 3 && sleep $DELAY \     # right-click
      && xdotool key r;                        # 'R' to remove space
   fi
   

   Make it executable with chmod +x ~/kdenlive_cut.sh

3. Open Settings...Keyboard, and go to the Shortcuts tab. Create a custom shortcut, naming it whatever you want, and setting the "Command" path to /home/username/kdenlive_cut.sh. Click Apply. The right-column will say "Disable", click on it and you'll see "New Accelerator": press your shortcut key combo. I chose Ctrl+Del since it doesn't conflict with the existing shortcuts in Kdenlive.

   

4. Now go to Kdenlive, and mark a segment you want to cut (as explained in Section 1). Click on that segment to outline it in red, and without moving the cursor, press Ctrl+Del; you will see the segment deleted, an empty space appear, the right-click menu show and the space removed -- all in the space of about 2 seconds.

   • Sometimes the shortcut fails the very first time it's invoked, giving you the longer right-click menu or the "Insert Space" option. Just cancel, and try it again...it works.

   • Here's a Youtube Demo of the shortcut in action.

ffmpeg

ffmpeg -i source.mp4 -ss 00:00:00 -t 00:00:00 -vcodec copy -acodec copy splice.mp4

This will take source.mp4 and, using the same audio and video codecs and not degrading quality, take -t time after -ss start time video and output your splice.mp4

Please note that the timing is very sensitive to formatting (above is one example formatting). Also, in some distributions, ffmpeg has been replaced with avconv. Simply run the above command and replace the word ffmpeg with avconv to solve this.

Another excellent source of information on this topic. (Thanks @pbhj)