Fair Use Clause, Copyright Act of 1976
"Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include—
(1) the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
(2) the nature of the copyrighted work;
(3) the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
(4) the effect of the use upon the potential market for or value of the copyrighted work.
The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors."
I'm not a lawyer, but this law gives you very generous flexibility if you learn from it and teach with it, with material that might otherwise be prohibited from copying. Use it wisely and respectfully.
YouTube Player Settings
This one is pretty easy and right under your nose. Anytime you watch a video, click on the little gear in the lower right corner. You can change the speed of the video right there in the player. It's a nice quick fix if you just need to slow a guitar part down but don't want to go through a bunch of steps to go to a youtube converter, download the file, download an audio program like Audacity, and slow down the file. The only drawback is that you're limited to half speed or quarter speed. If you want smaller increments, use a player like Audacity. Watching a long video? You can also speed it up to 1.25 speed and save yourself a couple minutes.
YouTube period.
YouTube has gotten to the point where all of the old vhs instructional videos have been uploaded to the platform already-- I'm talking about all the old REH and Hotlicks instructionals that are worth their weight in gold. Some of the VHS copies are so obscure they're out of print and/or selling for enormous amounts on ebay and amazon. And, there are lots of great players out there who have transcribed or covered many of your favorite solos and licks. Just go look!
Audacity
Audacity is a totally free open-source audio program for Mac or PC that will slow down music, or change the pitch, or loop a section, or all 3 at the same time. It's really one of my favorite practice tools. Got a fast guitar part you want to learn? Audacity. Want to learn a baritone guitar part but you only have a normal guitar and you don't want the floppiness of the strings? Audacity. Want to practice that fast baritone guitar part a thousand times without taking your hands off the instrument? Audacity.
Here is a great tool for slowing down all those shreddy guitar licks and solos.
Band In A Box
I've really only scratched the surface of Band In A Box since I got it but here it is in a nutshell: It's like having a team of world-class musicians at your beck and call, 24/7, they don't mind if you take all the solos, they won't complain, and they won't get tired or steal your beer.
I think it's a great tool for learning how to improvise: plug in whatever chords you feel like, choose whatever style you want, and go. Learn a new scale and you need to put the time into getting to know it? Put it in BIAB. Need to polish up on your [insert name of super obscure style] licks before you sub for that one band? Put it in BIAB.
The best tool for learning improvisation for any instrument, not just guitar.
VLC
VLC is a great video player that will play just about any format, so you can spend less time researching video players and spend more time watching your old guitar video files. It's very versatile and has a wide array of playback speed options too for when you want to transcribe all of those old Guthrie Govan bluesjamtrack videos.
Slow down all those videos by Joe Schmoe YouTuber who is just unbelievably talented on the guitar.
Convert2mp3.net
I know, I might catch some flak for mentioning this. The truth is, there is just more amazing material popping up on YouTube than the publishing companies can keep up with. And in order to learn it, you gotta slow it down and practice it. There is just too much amazing information out there and at our fingertips to say no. This is a great resource for converting youtube videos to files you can download.
Download all those videos by Joe Schmoe YouTuber so you can figure out all his guitar parts.