al7 I agree it would be nice to download only a part of a video, but instead you can use this to save file storage space.
Download the whole video, once downloaded you can throw away what you don't want.
- to cut a section from video using specific time length of cut, i.e. take the input video input.mp4, and extract 10 minutes from it starting from 00:05:20 (5 minutes and 20 second mark), i.e. the output video will the original but from 00:05:20 to 00:15:20.
$ ffmpeg -i input.mp4 -ss 00:05:20 -t 00:10:00 -c:v copy -c:a copy output1.mp4
- to cut a section from a video from time1 to time2, here 5 minutes 10 seconds to 15 minutes and 30 seconds
$ ffmpeg -i input.mp4 -ss 00:05:10 -to 00:15:30 -c:v copy -c:a copy output2.mp4
You can google where to get ffmpeg, and how to do many other things with it.