I use "The Amazing Slow Downer" software. It changes tempo, loops all or parts of tunes, and a lot more. I especially like the fact the is supports playlists. It can access tunes in different directories a single playlist.
Always playing with recorded material can serve as a "crutch which prevents someone from concentrating and using their memory. Note that I am not saying NEVER play with recorded music. But playing along with rhythm tracks makes the player think and realize when they have encountered a problem. I have "Band in a Box" which allows the user to create customized rhythm tracks. If you are curious about what they sound like, go to the "fbbts.com" and try playing along with recorded rhythm tracks.
I don't understand the original post...what do you mean by identify the mp3s? Do you have a folder full that you can't identify? Sorry...I'm confused. I don't know exactly what you are saying, but I personally like to learn things very slowly, just to get inside the tune enough to figure out how I feel like doing things. Of course, I also just like playing things slow too, slower than normal...but I was like that before I ever took up fiddling. I used to play a few small gigs here, just my guitar and singing, and there in rural places and small towns nearby, and people always noticed how much slower I took everything than most others do it. Some liked it, some didn't...but that's neither here nor there...just saying...I do like learning and practicing slow, but I also play slow, but I don't think the learning slow has anything to do with my playing the finished tune slow, because I've always done it that way, like,since I was ten years old...lol. But I might be missing the whole point.