MPlayer2 came about more than two years ago and has brought new changes/features over the original MPlayer video player. But now this weekend it was reported in a thread on the forums that a new fork was made.
This new fork is called MPV. As to why there's now another fork of MPlayer/Mplayer2, the developer explains, "MPlayer wants to maintain old code, even if it is very bad code. It seems mplayer2 was forked because MPlayer developers refused to get rid of all the cruft. The mplayer2 and MPlayer codebases also deviated enough to make a reunification unlikely. mplayer2 development is slow, and it is hard to get in changes. Details withheld as to not turn this into a rant. MPlayer rarely merged from mplayer2, and mplayer2 practically stopped merging from MPlayer (not even code cleanups or new features are merged) mpv intends to continuously merge from mplayer-svn and mplayer2, while speeding up development. There is willingness for significant changes, even if this means breaking compatibility."
Per the changes file of features MPV has over MPlayer2 include improved Microsoft Windows support, removal of dead platforms, support for playing URLs of popular streaming sites directly (e.g. YouTube), improved OpenGL output, dropped teletext support, new encoding functionality, and much more.
More information on this new MPlayer fork can be found via the MPV-Player GitHub page.