Buying the music gets you a far better listening experience than what you’d get on YouTube. That said, unless you really like a given piece of music, just saving something that you find appealing to your YouTube “liked” videos will build a library of sorts, with the exception of videos being deleted which happens.
... with the exception of videos being deleted which happens.
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You are correct about that. I went looking for the original version of Glen Frey’s “You belong to the city”. Great video. Apparently gone forever. If it’s not on YouTube it might as well not exist.