There are many ways to download youtube videos, but in case of a scenario where you want to download portion of a youtube video and not the full length video, here is a simple tip while helps you avoid downloading the whole video (like a speech, new cover etc) and get only part of the online video in any format you need.

Clip Converter
Clip Converter is a very cool online video conversion tool, which lets you to convert nearly any audio or video from a URL (YouTube, Vimeo, Dailymotion, MySpace, Veoh…) to any known popular media formats.

How to use Clipconverter.cc
1. Copy the Youtube Video Link
2. Visit Clipconverter.cc Website.Website
3. Paste the copied video link into the clipconverter Video URL field and click on continue button.
4. Then select the video quality and conversion format either in audio format (or) video format such as Mp4, 3gp, AVI, MOV etc.
5. Once video format is selected, you will find conversion option listed below, un-check the “Start of video” and enter the starting time from were you want the video to be downloaded and also specify the end time by un-checking “End of video”.
6. Now click on “Start” button to begin conversion process.
7. Wait for few seconds for conversion.
Once conversion processed, click download to save converted youtube video parts into computer.

http://trillionclues..com.ng/2016/12/how-to-download-specific-parts-of.html