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Tue Jan 2 18:26:00 CET 2007 · https://ffmpeg.org/pipermail/ffmpeg-devel/2007-January/026934.html

Hi

the attached patch rotates the residual by 180? for every 2nd frame
before performing the wavelet transform (!only encoding is implemented!)
i tested it with a single file and it gave +0.10 PSNR

more testing is welcome
decoding support is welcome too
and comments about this are even more welcome

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Democracy is the form of government in which you can choose your dictator
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Index: libavcodec/snow.c
===================================================================

--- libavcodec/snow.c	(revision 7401)
+++ libavcodec/snow.c	(working copy)
@@ -471,6 +471,7 @@
 #define ME_CACHE_SIZE 1024
     int me_cache[ME_CACHE_SIZE];
     int me_cache_generation;
+    int flip;
     slice_buffer sb;
 
     MpegEncContext m; // needed for motion estimation, should not be used for anything else, the idea is to make the motion estimation eventually independant of MpegEncContext, so this will be removed then (FIXME/XXX)
@@ -2166,7 +2167,7 @@
 
 //    assert(score==256*256*256*64-1);
     assert(iscore < 255*255*256 + s->lambda2*10);
-    assert(iscore >= 0);
+//    assert(iscore >= 0);
     assert(l>=0 && l<=255);
     assert(pl>=0 && pl<=255);
 
@@ -4058,6 +4059,19 @@
     return 0;
 }
 
+static void flip(int *buf, int w, int h){
+    int x,y;
+    for(y=0; y<h; y++){
+        for(x=0; x<w; x++){
+            int idx0= x + y*w;
+            int idx1= w-x-1 + (h-y-1)*w;
+            if(idx0>=idx1)
+                break;
+            FFSWAP(int, buf[idx0], buf[idx1]);
+        }
+    }
+}
+
 static int encode_frame(AVCodecContext *avctx, unsigned char *buf, int buf_size, void *data){
     SnowContext *s = avctx->priv_data;
     RangeCoder * const c= &s->c;
@@ -4204,6 +4218,9 @@
             }
         }
 
+        if(++s->flip & 1)
+            flip(s->spatial_dwt_buffer, w, h);
+
         ff_spatial_dwt(s->spatial_dwt_buffer, w, h, w, s->spatial_decomposition_type, s->spatial_decomposition_count);
 
         if(s->pass1_rc && plane_index==0){
@@ -4244,6 +4261,8 @@
         }
 
         ff_spatial_idwt(s->spatial_dwt_buffer, w, h, w, s->spatial_decomposition_type, s->spatial_decomposition_count);
+        if(s->flip & 1)
+            flip(s->spatial_dwt_buffer, w, h);
         if(s->qlog == LOSSLESS_QLOG){
             for(y=0; y<h; y++){
                 for(x=0; x<w; x++){
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Showing content from https://ffmpeg.org/pipermail/ffmpeg-devel/2007-January/026934.html below:

[Ffmpeg-devel] [RFC, Request for testing, PATCH] snow wavelet fliping