MPlayer 1.5 is the latest version and is compatible with the latest FFmpeg release (5.0) and FFmpeg development version (FFmpeg master).
The tarball already includes an FFmpeg snapshot, so you don't need to fetch it separately.
The tarballs are compressed with xz, for compatibility they are available with gzip compression too. Please get the xz variant if you can, to save bandwidth.
MPlayer is a movie player which runs on many systems (see the documentation). It plays most MPEG/VOB, AVI, Ogg/OGM, VIVO, ASF/WMA/WMV, QT/MOV/MP4, RealMedia, Matroska, NUT, NuppelVideo, FLI, YUV4MPEG, FILM, RoQ, PVA files, supported by many native, XAnim, and Win32 DLL codecs. You can watch VideoCD, SVCD, DVD, 3ivx, DivX 3/4/5, WMV and even H.264 movies.