framerate conversion using framestep filter

diff -ru --exclude CVS mplayer.orig/libmpcodecs/vf_framestep.c mplayer/libmpcodecs/vf_framestep.c
--- mplayer.orig/libmpcodecs/vf_framestep.c	2003-11-28 14:05:01.000000000 +0100
+++ mplayer/libmpcodecs/vf_framestep.c	2003-11-28 13:20:09.000000000 +0100
@@ -45,6 +45,17 @@
  * As usual it depends on what you're doing.
  *
  *     Daniele Forghieri ( [email protected] )
+ *
+ * patch by [email protected]:
+ *
+ * you can specify a "keep"-ratio by giving 2 instead of only one
+ * integer parameters. This gives a ratio of frames, that should be
+ * kept, e.g. if you use framestep=3:4, you get three quarters of the
+ * total number of frames, meaning the framerate is reduced to tree
+ * quartes of it. This is particular useful for converting NTSC
+ * material to mpeg: use framestep=2500/2997 to get a framerate of
+ * 25.0 out of material with a framerate of 29.97!
+ *
  */
 
 #include <stdio.h>
@@ -64,12 +75,56 @@
 /* Uncomment if you want to print some info on the format */
 // #define DUMP_FORMAT_DATA
 
+/* rational numbers */
+static int64_t greatest_common_divisor(int64_t a, int64_t b) {
+  if(a == 0 || b == 0) return 0;  // gcd(0, x) = gcd(x, 0) = 0
+
+  if(a < 0) {      // make sure that the two integers are non-negative
+    a = -a;
+  }
+
+  if(b < 0) {
+    b = -b;
+  }
+
+  int64_t t = 1;       // and perform Euklid's algorithm
+  while(t != 0) {
+    t = a % b;
+    a = b;
+    b = t;
+  }
+
+  return a;
+}
+
+static void rat_reduce(int64_t* num, int64_t* denom) {
+  if(*num == 0) {
+    *denom = 1;
+    return;
+  }
+
+  int64_t gcd = greatest_common_divisor(*num, *denom);
+  *num   /= gcd;
+  *denom /= gcd;
+}
+
+static void rat_add_to(int64_t* s_num, int64_t* s_denom,
+                       int64_t a_num, int64_t a_denom,
+                       int64_t b_num, int64_t b_denom) {
+    *s_num = a_num * b_denom + b_num * a_denom;
+    *s_denom = a_denom * b_denom;
+    rat_reduce(s_num, s_denom);
+}
+
 /* Private data */
 struct vf_priv_s {
     /* Current frame */
     int  frame_cur;
     /* Frame output step, 0 = all */
-    int  frame_step;
+    int64_t  frame_step;
+    int64_t  frame_step_denom;
+    int64_t  ratio_count;
+    int64_t  ratio_count_denom;
     /* Only I-Frame (2), print on I-Frame (1) */
     int  dump_iframe;
 };
@@ -98,11 +153,28 @@
         skip = mpi->pict_type == 1 ? 0 : 1;
     }
     else {
+      if (priv->frame_step_denom == 1) {
         /* Only 1 every frame_step */
         skip = 0;
         if ((priv->frame_step != 0) && ((priv->frame_cur % priv->frame_step) != 0)) {
             skip = 1;
         }
+      } else {
+        /* keep drop_ratio (rational) frames */
+        int64_t old_int = 0;
+        int64_t new_int = 0;
+
+        old_int = priv->ratio_count / priv->ratio_count_denom;
+        rat_add_to(&priv->ratio_count, &priv->ratio_count_denom,
+                   priv->ratio_count, priv->ratio_count_denom,
+                   priv->frame_step, priv->frame_step_denom);
+        new_int = priv->ratio_count / priv->ratio_count_denom;
+        if (old_int < new_int) {
+          skip = 0;
+        } else {
+          skip = 1;
+        }
+      }
     }
     /* Increment current frame */
     ++priv->frame_cur;
@@ -170,11 +242,19 @@
                 }
 
                 if (*args != '\0') {
-                    p->frame_step = atoi(args);
-                    if (p->frame_step <= 0) {
-                        printf("Error parsing argument\n");
-                        return(0);
-                    }
+                  int64_t num = 0;
+                  int64_t denom = 1;
+                  int scaned = sscanf(args, "%d:%d", &num, &denom);
+                  if ((scaned == 0) || /* no args scaned */
+                      (num <= 0)) {    /* drop every -4th frame? */
+                    printf("Error parsing arguments: scaned=%d, num=%d, denom=%d\n", scaned, num, denom);
+                    return(0);
+                  }
+                  rat_reduce(&num, &denom);
+                  p->frame_step = num;
+                  p->frame_step_denom = denom;
+                  p->ratio_count = 0;
+                  p->ratio_count_denom = 1;
                 }
             }
         }

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.3 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQE/x1bTB6g1EUxThvcRAt4sAKCP4T7NnWgKb67q6+hY0lK/6wtkqgCeJOTR
9NjoQ9Wi+XAxzoxiCbintFU=
=uOHj
-----END PGP SIGNATURE-----