Problem:

You have a video and just need cut a part and save!. You don’t need to re-encode the video.

Solution 1: Using ffmpeg in bash

INPUT="/media/rogelio/curso-linux/Sesion 6.mp4"
OUTPUT="/media/rogelio/curso-linux/output.mp4"

ffmpeg -i "$INPUT" -ss 00:27:43 -to 03:05:57 -vcodec copy -acodec copy "$OUTPUT"

⚠️ Note: If you need to use a more precise unit, less than a second, you need to reencode the video (not copy vcodec or acodec). Example cut video from 0.5 to 12 seconds:

ffmpeg -i "$INPUT" -ss 00:00:0.5 -to 00:00:12 -c:v libx264 -acodec copy  "$OUTPUT" && xdg-open $OUTPUT

Solution 2: Using Kdenlive software

If you are in for the easy graphical interface, then there’s actually a way to do this:

  1. Start Kdenlive or start new empty project.
  2. Drag your source video clip into the project bin.
  3. Select your clip, so it gets shown in the clip monitor.
  4. Use the clip monitor controls to play and pause, etc.
  5. To set the start point: this is termed in “in” point by simply pressing the “I” key. A marker will appear on the time scale in the clip monitor.
  6. To set the end point or “out” point: press the “O” key. A second marker appears and the region in between is highlighted.
  7. Right click in the monitor and select “save region” (or “Extract zone” in version 22).
  8. Enter new filename, click ok.
  9. Your clip in the project bin will show a progress bar. Wait for it to disappear.

Source:

https://thediveo-e.blogspot.com/2013/09/trimming-video-files-lossless-using.html
https://forum.kde.org/viewtopic.php?f=265&t=130552&p=459516#p459516