YouTube doesn’t offer an option to download the videos you watch there. Either they don’t want you to download them or they believe streaming is all you really need to do. What they don’t understand is streaming doesn’t always work very well, even with buffering.
Add data throttling by certain ISPs to the mix, and it can seem painful to watch any streaming videos and not just from YouTube.
I’ve tested a few add-ons for Firefox and a few extensions for Chrome. They only seem to work correctly for a limited time. I can only guess the code is being changed at YouTube to defeat them. There are other methods, such as dedicated video downloading apps, but I rarely use them.
In fact, I have a dedicated app on Linux Mint that I prefer using when I want to watch a video without being connected to the internet (usually a long documentary). It’s a “snap” package called “Video Downloader”.
I suppose it depends on whom you listen to. Downloading anything from the Internet isn’t inherently illegal. Copyright infringement only occurs when distributing (as in uploading and sharing). Certain entities (like the MPAA and RIAA) like to say it’s stealing if you don’t download something using an approved method.
Everything on the web is downloaded in one form or another, even streaming video. It’s how it all works. The issues arise when you try to share it online. Don’t do it and that’s all I can say about that. If you noticed it in the news, the RIAA tried to get GitHub to take down a popular library called “youtube-dl”. They succeeded but only temporarily. The backlash was tremendous.
Every PC and mobile device has a video player of some kind available. Sometimes one is installed from the beginning, and sometimes you have to download something.
I like VLC. The versions that work or Windows, Linux and on my Android phone work very well for me. I’ve even watched full-length movies on my phone, without them sucking the battery dry on the rare occasions that I do.
Most of the videos I download are freely distributed documentaries. They’re boring enough that if I have to suffer from long pauses on YouTube, I probably wouldn’t continue to watch them.
Of course, you can now watch full movies on YouTube (distributed by YouTube), both free and commercial. It would really suck to be stuck watching a movie you paid for that pauses every couple of minutes. I don’t think the folks at Google (who owns YouTube) would have a major problem with people downloading the things they pay for. I’m just guessing, of course, because they may not like it at all.