detect when iterative_me fails to converge, and stop searching

Originally committed as revision 4868 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/snow.c

@@ -25,6 +25,8 @@
 
 #include "mpegvideo.h"
 
+#include <zlib.h>
+
 #undef NDEBUG
 #include <assert.h>
 
@@ -3301,6 +3303,8 @@ static void iterative_me(SnowContext *s){
     const int b_height= s->b_height << s->block_max_depth;
     const int b_stride= b_width;
     int color[3];
+    const int first_crc_pass= 12;
+    uint32_t crcs[50];
 
     for(pass=0; pass<50; pass++){
         int change= 0;
@@ -3435,6 +3439,18 @@ static void iterative_me(SnowContext *s){
             }
         }
         av_log(NULL, AV_LOG_ERROR, "pass:%d changed:%d\n", pass, change);
+
+        if(pass >= first_crc_pass){
+            int i;
+            //FIXME can we hash just the blocks that were analysed?
+            crcs[pass]= crc32(crc32(0,NULL,0), (void*)s->block, b_stride*b_height*sizeof(BlockNode));
+            for(i=pass-1; i>=first_crc_pass; i--){
+                if(crcs[i] == crcs[pass]){
+                    change= 0;
+                    break;
+                }
+            }
+        }
         if(!change)
             break;
     }

tests/ffmpeg.regression.ref

@@ -119,10 +119,10 @@ a7ef4746f27be309138c188e327d3ebe *./data/a-ffv1.avi
 2653642 ./data/a-ffv1.avi
 799d3db687f6cdd7a837ec156efc171f *./data/out.yuv
 stddev:  0.00 PSNR:99.99 bytes:7602176
-97c7066617d9e6c86a43a2736b3e9f16 *./data/a-snow.avi
-1190760 ./data/a-snow.avi
-7e4d9c61252ff22b1a0d4e892cc1d957 *./data/out.yuv
-stddev:  2.89 PSNR:38.87 bytes:7602176
+b7e88c743458e60d59d83554d1e1ace5 *./data/a-snow.avi
+1191118 ./data/a-snow.avi
+2e0cda9acd71d339d72372a22591500a *./data/out.yuv
+stddev:  2.90 PSNR:38.87 bytes:7602176
 11fd61ee7e67ef7a7b2a3df973691305 *./data/a-snow53.avi
 3533710 ./data/a-snow53.avi
 799d3db687f6cdd7a837ec156efc171f *./data/out.yuv