Some points:

• Yes, it’s doable. Use mplayer2-build helper
• You have to install many things (mainly autotools and don’t forget system audio header). Also yasm from opencsw
• With regard to autotools, you have to create symlink for few things and put it somewhere in your PATH, preferably before everything else (namely ginstall -> install, aclocal-1.10 -> aclocal, automake-1.10 -> automake)
• Add –cc=gcc to common_options

Probably there are some more but that’s all I can remember right now. Should also applicable for opensolaris (why are you still using it) and Solaris Express 11.

If you want to enable SSE support, you have to apply some patches to mplayer.

If you want to use vdpau while using nvidia’s latest driver, you have to install libvdpau.