Downloading science lectures to iPad, such as MIT Open Courseware and other university classes.

I like to download science courses to my iPad and watch them in my spare time when I don't necessarily have an Internet connection. A lot of the video lectures say "View in iTunes." If you click that post demise of iTunes, a MacBook asks you if you want to open the file in Podcasts. Podcasts is also where Apple put most of the courses I had previously downloaded, when it did away with iTunes. But podcasts don't have video, only audio. And most science lectures are pretty useless without the video.

Sometimes MIT Open Courseware classes have a link to an Internet archive from which you can download. But sometimes they don't.

Then some professors put their stuff on Youtube; but Youtube doesn't let you download.

Any suggestions?