If you want to cut out a part of a video, we recommend using ffmpeg.
1. install ffmpeg
Download ffmpeg corresponding to the OS you are using from the following URL
https://www.ffmpeg.org/download.html
2. cut out the video
Go to the folder where the video is saved and execute the following command.
ffmpeg -ss [start seconds] -i input.mp4 -t [video seconds] -c copy out.mp4
For example, to cut out 30-40 minutes from a 1 hour long video, execute the following command.
ffmpeg -ss 1800 -i input.mp4 -t 600 -c copy out.mp4