use downmixing coefficients in dca decoder.

reference:
Subject: [Ffmpeg-devel] [PATCH] DTS multichannel
Date: Wed, 25 Apr 2007 16:25:18 -0400

Originally committed as revision 8875 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dca.c

@@ -522,11 +522,19 @@ static int dca_subframe_header(DCAContext * s)
     }
 
     /* Stereo downmix coefficients */
-    if (s->prim_channels > 2 && s->downmix) {
+    if (s->prim_channels > 2) {
+        if(s->downmix) {
         for (j = 0; j < s->prim_channels; j++) {
             s->downmix_coef[j][0] = get_bits(&s->gb, 7);
             s->downmix_coef[j][1] = get_bits(&s->gb, 7);
         }
+        } else {
+            int am = s->amode & DCA_CHANNEL_MASK;
+            for (j = 0; j < s->prim_channels; j++) {
+                s->downmix_coef[j][0] = dca_default_coeffs[am][j][0];
+                s->downmix_coef[j][1] = dca_default_coeffs[am][j][1];
+            }
+        }
     }
 
     /* Dynamic range coefficient */
@@ -750,18 +758,18 @@ static void lfe_interpolation_fir(int decimation_select,
 }
 
 /* downmixing routines */
-#define MIX_REAR1(samples, si1) \
-     samples[i] += samples[si1]; \
-     samples[i+256] += samples[si1];
+#define MIX_REAR1(samples, si1, rs, coef) \
+     samples[i]     += samples[si1] * coef[rs][0]; \
+     samples[i+256] += samples[si1] * coef[rs][1];
 
-#define MIX_REAR2(samples, si1, si2) \
-     samples[i] += samples[si1]; \
-     samples[i+256] += samples[si2];
+#define MIX_REAR2(samples, si1, si2, rs, coef) \
+     samples[i]     += samples[si1] * coef[rs][0] + samples[si2] * coef[rs+1][0]; \
+     samples[i+256] += samples[si1] * coef[rs][1] + samples[si2] * coef[rs+1][1];
 
-#define MIX_FRONT3(samples) \
+#define MIX_FRONT3(samples, coef) \
     t = samples[i]; \
-    samples[i] += samples[i+256]; \
-    samples[i+256] = samples[i+512] + t;
+    samples[i]     = t * coef[0][0] + samples[i+256] * coef[1][0] + samples[i+512] * coef[2][0]; \
+    samples[i+256] = t * coef[0][1] + samples[i+256] * coef[1][1] + samples[i+512] * coef[2][1];
 
 #define DOWNMIX_TO_STEREO(op1, op2) \
     for(i = 0; i < 256; i++){ \
@@ -769,10 +777,17 @@ static void lfe_interpolation_fir(int decimation_select,
         op2 \
     }
 
-static void dca_downmix(float *samples, int srcfmt)
+static void dca_downmix(float *samples, int srcfmt,
+                        int downmix_coef[DCA_PRIM_CHANNELS_MAX][2])
 {
     int i;
     float t;
+    float coef[DCA_PRIM_CHANNELS_MAX][2];
+
+    for(i=0; i<DCA_PRIM_CHANNELS_MAX; i++) {
+        coef[i][0] = dca_downmix_coeffs[downmix_coef[i][0]];
+        coef[i][1] = dca_downmix_coeffs[downmix_coef[i][1]];
+    }
 
     switch (srcfmt) {
     case DCA_MONO:
@@ -785,21 +800,21 @@ static void dca_downmix(float *samples, int srcfmt)
     case DCA_STEREO:
         break;
     case DCA_3F:
-        DOWNMIX_TO_STEREO(MIX_FRONT3(samples),);
+        DOWNMIX_TO_STEREO(MIX_FRONT3(samples, coef),);
         break;
     case DCA_2F1R:
-        DOWNMIX_TO_STEREO(MIX_REAR1(samples, i + 512),);
+        DOWNMIX_TO_STEREO(MIX_REAR1(samples, i + 512, 2, coef),);
         break;
     case DCA_3F1R:
-        DOWNMIX_TO_STEREO(MIX_FRONT3(samples),
-                          MIX_REAR1(samples, i + 768));
+        DOWNMIX_TO_STEREO(MIX_FRONT3(samples, coef),
+                          MIX_REAR1(samples, i + 768, 3, coef));
         break;
     case DCA_2F2R:
-        DOWNMIX_TO_STEREO(MIX_REAR2(samples, i + 512, i + 768),);
+        DOWNMIX_TO_STEREO(MIX_REAR2(samples, i + 512, i + 768, 2, coef),);
         break;
     case DCA_3F2R:
-        DOWNMIX_TO_STEREO(MIX_FRONT3(samples),
-                          MIX_REAR2(samples, i + 768, i + 1024));
+        DOWNMIX_TO_STEREO(MIX_FRONT3(samples, coef),
+                          MIX_REAR2(samples, i + 768, i + 1024, 3, coef));
         break;
     }
 }
@@ -980,7 +995,7 @@ static int dca_subsubframe(DCAContext * s)
     /* Down mixing */
 
     if (s->prim_channels > dca_channels[s->output & DCA_CHANNEL_MASK]) {
-        dca_downmix(s->samples, s->amode);
+        dca_downmix(s->samples, s->amode, s->downmix_coef);
     }
 
     /* Generate LFE samples for this subsubframe FIXME!!! */

libavcodec/dcadata.h

@@ -8361,6 +8361,19 @@ static const float dca_downmix_coeffs[65] = {
   0.001412537544623, 0.001000000000000, 0.000501187233627, 0.000251188643151, 0.000000000000000,
 };
 
+static const uint8_t dca_default_coeffs[16][5][2] = {
+    { { 13, 13 },                                                 },
+    { {  0, 64 }, { 64,  0 },                                     },
+    { {  0, 64 }, { 64,  0 },                                     },
+    { {  0, 64 }, { 64,  0 },                                     },
+    { {  0, 64 }, { 64,  0 },                                     },
+    { {  6,  6 }, {  0, 25 }, { 25,  0 },                         },
+    { {  0, 25 }, { 25,  0 }, { 13, 13 },                         },
+    { {  6,  6 }, {  0, 25 }, { 25,  0 }, { 13, 13 },             },
+    { {  0, 25 }, { 25,  0 }, {  0, 13 }, { 13,  0 },             },
+    { {  6,  6 }, {  0, 25 }, { 25,  0 }, {  0, 13 }, { 13,  0 }, },
+};
+
 /* downmix coeffs
 
  TABLE 9