One minor nitpick. Could you fill in the comments bit?
 #define EMPEG_HIJACK_INJECTBUTTONS	_IO(EMPEG_DISPLAY_MAGIC, 90)	// Inject button codes into player's input queue

+#define EMPEG_HIJACK_GETPLAYERBUFFER _IO(EMPEG_DISPLAY_MAGIC, 91) // Inject button codes into player's input queue
+#define EMPEG_HIJACK_GETPLAYERUIFLAGS _IO(EMPEG_DISPLAY_MAGIC, 92) // Inject button codes into player's input queue