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.
Download Only Parts, Portion of Online Videos (Youtube, Vimeo, Dailymotion etc)
Use cool online video conversion tool, which lets you convert nearly any audio or video from a URL (YouTube, Vimeo, Dailymotion, MySpace, Veoh…) to any known popular media formats.
# Go to http://sh.st/IyMEO
Simply enter the URL from your video page, and the web application will try to detect the video file. Afterwards the Converter will grab the media file to their server. From there its converted to the chosen format and then after completing the conversion you can download the media file.
Download Only Parts, Portion of Online Videos
The best feature it provides is that there are few settings you can make prior to the conversion, like specifying a portion of the video to be downloaded, sound and video quality etc. You can also upload the video files for conversion.
Source: ACCRA24.COM & GHANASKY.COM but Credit to Snap How