People interested in AACS technologies should have a look at libaacs. NB: Most commercial Blu-Ray are protected by AACS orīD+ technologies and this library is not enough to playback those discs.
This research project is developed by an international team of developers from Doom9. Libbluray is an open-source library designed for Blu-Ray Discs playback for media players, like VLC or MPlayer.