diff -Nur MPlayer.orig/libvo/aspect.c MPlayer/libvo/aspect.c
--- MPlayer.orig/libvo/aspect.c	2004-10-28 03:15:51.000000000 +0200
+++ MPlayer/libvo/aspect.c	2005-08-24 15:34:14.000000000 +0200
@@ -11,13 +11,16 @@
 #include <stdio.h>
 #endif
 
+int vo_physical_width = 0;
+int vo_physical_height = 0;
+
 int vo_panscan_x = 0;
 int vo_panscan_y = 0;
 float vo_panscan_amount = 0;
 
 #include "video_out.h"
 
-float monitor_aspect=4.0/3.0;
+float monitor_aspect=-1.0f;
 extern float movie_aspect;
 
 static struct {
@@ -47,11 +50,24 @@
   aspdat.preh = preh;
 }
 
+static void init_monitor_aspect( void )
+{
+ if (monitor_aspect != -1.0f) return;
+ if (vo_physical_width == 0 || vo_physical_height == 0) {
+  // if there's no other indication, assume square pixels
+  vo_physical_width = aspdat.scrw;
+  vo_physical_height = aspdat.scrh;
+ }
+ mp_msg(MSGT_VO,MSGL_V,"\naspect: monitor aspect detected %d:%d\n", vo_physical_width, vo_physical_height);
+ monitor_aspect = 1.0f * vo_physical_width / vo_physical_height;
+}
+
 void aspect_save_screenres(int scrw, int scrh){
 #ifdef ASPECT_DEBUG
   printf("aspect_save_screenres %dx%d \n",scrw,scrh);
 #endif
   aspdat.scrw = scrw;
   aspdat.scrh = scrh;
+  init_monitor_aspect(); // now is a good time
 }
 
 /* aspect is called with the source resolution and the
diff -Nur MPlayer.orig/libvo/aspect.h MPlayer/libvo/aspect.h
--- MPlayer.orig/libvo/aspect.h	2002-06-05 21:35:54.000000000 +0200
+++ MPlayer/libvo/aspect.h	2005-08-24 00:08:35.000000000 +0200
@@ -2,6 +2,9 @@
 #define __ASPECT_H
 /* Stuff for correct aspect scaling. */
 
+extern int vo_physical_width;
+extern int vo_physical_height;
+
 extern int vo_panscan_x;
 extern int vo_panscan_y;
 extern float vo_panscan_amount;
diff -Nur MPlayer.orig/libvo/x11_common.c MPlayer/libvo/x11_common.c
--- MPlayer.orig/libvo/x11_common.c	2005-08-23 23:07:07.000000000 +0200
+++ MPlayer/libvo/x11_common.c	2005-08-23 23:42:31.000000000 +0200
@@ -464,6 +464,12 @@
         if (!vo_screenheight)
             vo_screenheight = DisplayHeight(mDisplay, mScreen);
     }
+    if (vo_physical_width == 0) {
+	vo_physical_width = DisplayWidthMM(mDisplay, mScreen);
+    }
+    if (vo_physical_height == 0) {
+	vo_physical_height = DisplayHeightMM(mDisplay, mScreen);
+    }
     // get color depth (from root window, or the best visual):
     XGetWindowAttributes(mDisplay, mRootWin, &attribs);
     depth = attribs.depth;