You're right, I just checked and I can't find mplayer on AlexT's repo.
However, I managed to install mplayer on my Edison by following the next steps:
#*I was missing yasm so I needed to install it. 1. wget http://www.tortall.net/projects/yasm/releases/yasm-1.3.0.tar.gz 2. tar xvf yasm-1.3.0.tar.gz 3. cd yasm-1.3.0 4. sed -i 's#) ytasm.*#)#' Makefile.in && 5. ./configure --prefix=/usr && 6. make #*make check to test results 7. make install #*cd ../ to go back to root directory 8. wget ftp://ftp.mplayerhq.hu/MPlayer/releases/MPlayer-1.1.1.tar.xz 9. tar xvf MPlayer-1.1.1.tar.xz 10. cd MPlayer-1.1.1 11. ./configure 12. make 13. make install
The process took a really long time but after this you should be able to run mplayer with the command ./mplayer I haven't tested it and I didn't enable GUI since Edison doesn't have one but the installation was correct.
You can find more info about mplayer and yasm in: