MPlayer previously contained source from the OpenDivX project, which disallows binary redistribution.This code has been removed in version 0.90-pre1 and the remaining file divx_vbr.c that is derived from OpenDivX sources has been put under the GPL by its authors as of version 0.90pre9. You are now welcome to create binary packages as you see fit.
Another impediment to binary redistribution was compiletime optimizations for CPU architecture. MPlayer now supports runtime CPU detection (pass the --enable-runtime-cpudetection to configure). It is disabled by default because it implies a small speed sacrifice, but it is now possible to create binaries that run on different members of the Intel compatible CPU family.