28 great Youtube video download services

Want to download a great Youtube video and watch it slowly? Today, I listed 28 Youtube video download services that are relatively easy to use at present, and of course, some other video sites are also involved in downloading. If you already have a few tools or services, this list should be comprehensive, and each one has been tested and absolutely works. In fact, one or two such services are sufficient, so why list so many? Compare the speed, each needs to need!