how do i play midi files
MIDI files will play from Windows 8.1 in Windows Media Player with no modifications or extra codecs if you use the default settings for Windows Media Player. It seems that without default settings, the MIDI codecs will not automatically load when trying to play a MIDI file for the first time.
I have a MIDI file example.mid on my Mac OS X 10.6 laptop. The laptop is connected to a MIDI keyboard (old Yamaha Clavinova, if it matters) via a Roland UM-One mk2 USB-MIDI interface. Using Apple's Audio MIDI Setup utility, I have configured the interface. Audio MIDI Setup's Test Setup feature will make my keyboard play notes.