mpv is a fork of mplayer2, which is a fork of MPlayer.
Original MPlayer Copyright file follows below.

MPlayer was originally written by Árpád Gereöffy and has been extended and
worked on by many more since then, see the AUTHORS file for an (incomplete)
list. MPlayer as a whole is copyrighted by the MPlayer team. Individual
copyright notices can be found in file headers.

Most files in MPlayer are licensed under the GNU General Public License,
version 2 with an explicit "or later" clause or a compatible license
(LGPL 2.1+, MIT/BSD). An exception are the files talloc.c and talloc.h,
which are LGPL 3+.
Thus MPlayer as a whole can be redistributed under terms compatible with
the GNU General Public License, version 3; see the LICENSE file for details.

MPlayer includes code from several external sources. General information and
license details are listed below:

Name:       a couple of files copied from FFmpeg
Version:    updated to different versions
URL:        http://www.ffmpeg.org
Directory:  compat/x86_cpu.h
Copyright:  Many, see individual files for copyright notices.
License:    GNU Lesser General Public License


Name:       dvbstream
Version:    0.4.3-pre3 (CVS checkout)
URL:        http://sourceforge.net/projects/dvbtools/
Directory:  stream/dvbin.h stream/stream_dvb.c
Copyright:  2001-2002 Dave Chapman <dave@dchapman.com>
License:    GNU General Public License


This is not a complete list. grep the sources for "Copyright".