MPlayer and its libraries are built using MinGW-w64 & MSYS2, a minimal Unix-like shell & collection of GNU utilities for Windows. The GCC version used is 4.9.2. A complete build environment and sources used to compile the libraries included in MPlayer are available here.
* Download the MSYS2 package and a MinGW toolchain. Extract MSYS2 anywhere in a path without spaces.
* Extract mingw32 and/or mingw64 to the MSYS2 directory.
* Edit 'etc\fstab' and the 'local_prefix' value in the gcc spec file accordingly:
- 32-bit: mingw32\lib\gcc\i686-w64-mingw32\4.9.2\specs
- 64-bit: mingw64\lib\gcc\x86_64-w64-mingw32\4.9.2\specs
* Launch the MSYS2 shell by executing 'mingw32_shell.bat' for 32-bit or 'mingw64_shell.bat' for 64-bit.