[MPlayer-dev-eng] [PATCH] -aspect-tolerance option to avoid tiny prescaling

[Kurt Garloff <kurt@xxxxxxxxxx>]

Attila,

On Fri, Mar 28, 2008 at 02:08:38PM +0100, Attila Kinali wrote:
> On Fri, 28 Mar 2008 13:51:07 +0100
> Kurt Garloff <kurt@xxxxxxxxxx> wrote:
> 
> > In general I think we should avoid scaling if the difference in
> > aspect ratio is tiny.
> > 
> > Attached patch does this for AVI files.
> 
> This code belongs into libvo/aspect.c
> 
> You should also make the limit configurable by adding a command
> line option. It should be also possible to switch this "protection"
> off (in some cases, the resulting black bars are more annoying).

Thanks for the good feedback!

I could not find a clean way to add the logic to libvo/aspect.c, as
the prescaling is configured before that code gets called.

A new patch attached, putting the logic into libmpcodecs/vd.c, making
it adjustable (-aspect-tolerance FLOAT) and documenting it.

Best,
-- 
Kurt Garloff                   <kurt@xxxxxxxxxx>             [Koeln, DE]
Physics:Plasma modeling <garloff@xxxxxxxxxxxxxxxxxxx> [TU Eindhoven, NL]
Linux: VP PM OPS               <garloff@xxxxxxx>            [Novell Inc]

--- mplayer/libmpcodecs/vd.c.orig	2008-03-24 14:31:42.000000000 +0100
+++ mplayer/libmpcodecs/vd.c	2008-03-31 10:22:17.000000000 +0200
@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <math.h>
 
 #include "config.h"
 #include "mp_msg.h"
@@ -118,6 +119,7 @@ int opt_screen_size_x=0;
 int opt_screen_size_y=0;
 float screen_size_xy=0;
 float movie_aspect=-1.0;
+float aspect_tolerance=0.01;
 int vo_flags=0;
 int vd_use_slices=1;
 
@@ -278,10 +280,15 @@ csp_again:
      }
     }
     if(sh->aspect>0.01){
-      int w;
+      int w = screen_size_x;
+      float calc_aspect = (float)screen_size_x/screen_size_y;
       mp_msg(MSGT_CPLAYER,MSGL_INFO,MSGTR_MovieAspectIsSet,sh->aspect);
       mp_msg(MSGT_IDENTIFY, MSGL_INFO, "ID_VIDEO_ASPECT=%1.4f\n", sh->aspect);
-      w=(int)((float)screen_size_y*sh->aspect); w+=w%2; // round
+      // Avoid prescaling if the difference is tiny (rounding errors etc)
+      // so we don't do stupid things such as 1360x768 -> 1366x768
+      if (fabs(calc_aspect - sh->aspect) > aspect_tolerance) {
+        w=(int)((float)screen_size_y*sh->aspect); w+=w%2; // round
+      }
       // we don't like horizontal downscale || user forced width:
       if(w<screen_size_x || screen_size_xy>8){
         screen_size_y=(int)((float)screen_size_x*(1.0/sh->aspect));
--- mplayer/cfg-common.h.orig	2008-03-24 14:32:03.000000000 +0100
+++ mplayer/cfg-common.h	2008-03-31 10:24:19.000000000 +0200
@@ -231,6 +231,7 @@
         {"nozoom", &softzoom, CONF_TYPE_FLAG, 0, 1, 0, NULL},
 	{"aspect", &movie_aspect, CONF_TYPE_FLOAT, CONF_RANGE, 0.2, 3.0, NULL},
 	{"noaspect", &movie_aspect, CONF_TYPE_FLAG, 0, 0, 0, NULL},
+	{"aspect-tolerance", &aspect_tolerance, CONF_TYPE_FLOAT, CONF_RANGE, 0.0, 1.5, NULL},
 	{"xy", &screen_size_xy, CONF_TYPE_FLOAT, CONF_RANGE, 0.001, 4096, NULL},
 
         {"flip", &flip, CONF_TYPE_FLAG, 0, -1, 1, NULL},
@@ -348,6 +349,7 @@ extern char *mp_msg_charset;
 // codec/filter opts: (defined at libmpcodecs/vd.c)
 extern float screen_size_xy;
 extern float movie_aspect;
+extern float aspect_tolerance;
 extern int softzoom;
 extern int flip;
 
--- mplayer/DOCS/man/en/mplayer.1.orig	2008-03-24 14:31:56.000000000 +0100
+++ mplayer/DOCS/man/en/mplayer.1	2008-03-31 10:25:37.000000000 +0200
@@ -4262,6 +4262,21 @@ incorrect or missing in the file being p
 Disable automatic movie aspect ratio compensation.
 .
 .TP
+.B \-aspect\-tolerance <0.0\-1.5>
+When decoding, the video material is prescaled from the encoding 
+resolution to the advertised aspect ratio (e.g. from 720x576 
+encoded PAL information to 768x576 with 4:3 aspect). Prescaling does
+however result in a loss of quality for video material encoded with
+high bit rates. This option allows you to avoid prescaling in case 
+the difference between encoding resolution and the correct aspect
+ratio is small, which can happen due to rounding errors or sizes
+that are a tiny bit off the perfect ratio (e.g. 1360x768 vs. 1366x768).
+The value sets the maximum aspect ratio difference that the decoder
+should ignore at the expense of an apsect ratio that's a little bit
+off. Useful values are typically in the 0.00\-0.10 range 
+(default: 0.01).
+.
+.TP
 .B "\-field\-dominance <\-1\-1>"
 Set first field for interlaced content.
 Useful for deinterlacers that double the framerate: \-vf tfields=1,

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