How to tell which chords are used?

Hey all, I've found this collection of pretty cool backing tracks in various keys, but I have a small problem. I can see which key the backing tracks are in, since it's clearly written out, and there is a small list of scales recommended for soloing over. However, my problem is that I can't hear exactly which chords are being played, and thus it's hard for me to tell which notes to to play for the best possible sound. Any advice on what I can do to make it easier?