As it stands downloading videos to a PC is an infringement of YouTube’s terms and conditions.
It is almost certainly illegal as well, if you do not own the copyright or have permission from the copyright holder or distribute and benefit financially from the download.
Is downloading YouTube videos legal for personal use?
Downloading YouTube videos: what you need to know. Google, which owns YouTube, makes its money through advertising. For personal use, no it is not illegal to download YouTube video. But it is immoral.
Can you use YouTube videos without permission?
Really Long Answer: In most instances you can’t use any part of someone else’s video without the copyright creators permission. However, there are some exceptions or limitations to this. Fair Use permits limited use of copyrighted material without acquiring permission from the rights holders.
Is it safe to download YouTube videos?
Downloading videos from YouTube is a relatively safe bet, since it is unlikely to be carrying malware and you can view any video before you download it. You should use greater caution when acquiring a downloader program. Make sure the source of the download is reliable, and that the software itself is reputable.