This news is coming a few days late (MPlayer's web-site lacks any RSS or syndication support), but the latest MPlayer code in their SVN trunk now supports most HD-DVD and Blu-ray codecs. Earlier this year we talked about possible Blu-ray support for FFmpeg
and developers becoming more interested
after we interviewed the FFmpeg developers
and there ended up being an outpouring of support by our readers offering up Blu-ray drives and other forms of help.
The latest MPlayer code in their Subversion repository now supports most Blu-ray and HD-DVD codecs. MPlayer though cannot play any content "out of the box", but there is an MPlayer patch on the Doom9 Forums
that provides a library and patch to be applied against the latest SVN code that drops in Blu-ray playback support. There is also support for ripping legal copies of Blu-ray content on Linux using this guide
Finally it's becoming possible to play your legal Blu-ray movies on Linux. More details on the MPlayer web-site