A command-line program for video downloading. Works on multiple sites, not just YouTube.
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It's released to the public domain. Modify at will.
Pro Works in other places too
Can download from different sources, not just YouTube. (https://rg3.github.io/youtube-dl/supportedsites.html)
Pro Frequently updated
The developers keep up with YouTube-s meta changes. If the download of a video fails, just update to a new version and it should work.
Pro Ability to download different formats and meta-info
Works on Windows, Mac OS X and other Unix systems like Linux for example.