MPlayer includes a help file which specifies all the key combinations needed to control every functions on it. If you want you also can enable graphics system overlays which show the response to the controls (one bar when going up or down the volume, pause symbol, etc.)
MPlayer for Windows 2013-11-08 Build 119 Download
MPlayer plays a wide range of multimedia formats, with support for dozens of audio and video codecs, with a quick and agile response and low resource consumption.
Update: MPlayer for Windows 2014-01-13 Build 121
Software Informations:
Developer: LoRd_MuldeR
License: GPL / Price: $0
Size: 37.6MB
OS: Windows 8 / 7 / Vista / XP
Date Published: November 09, 2013