ClipGrab

Downloading videos from YouTube can have a number of uses for intervention.
-Downloaded vids don't have the sidebar of distraction from which students will ask to see other things.
-Or ads (another way to avoid these is to insert a video in a Google Slides presentation, sometimes also helpful because you can put a story grammar visual or other support on a following slide, or otherwise put the video in context)
-If you download, you can keep an archive as you wish
-Downloading helps you skirt blocking within a district, or poor wifi
-Occasionally I have found a video that is perfect to illustrate a concept except for one sweary or inappropriate-to-show part- in those cases I have downloaded and used iMovie to edit out that part.

Previously I have recommended a website to do this downloading, but it appears to have become no longer useful for the purpose. You can now download the free application ClipGrab from here for your Mac or PC. It's very easy to use, just copy the YouTube URL (the address at the top bar when the video is playing) and paste into the bar, or ClipGrab also lets you search YouTube from the application. Click Grab This Clip! and you can save to your Downloads folder.

To get started with YouTube clips with some great models of clinical uses, be sure to see Anna Vagin's website and books.