The DTS audio track has been ripped from the VIDEO_TS layer of the DVD-A disk of REM - Green. All the fruity interviews and other filler crap has been thrown away, with only the music to remain.
Burn it to a DVD, put it in your DVD player, and enjoy. Or if you're really cool, play it with your stand-alone media player.
(If you're wondering why it's so small, it's because the commercial release has the DTS track encoded at 768 Kbps instead of the more typical 1411 Kbps that is generally used for DTS.... whatever... it still sounds f'ing fantastic.)