Ticket #6569: mythtv_ac3gainfix.patch

libs/libavcodec/ac3dec.c

@@ -91 +91 @@
     LEVEL_MINUS_9DB
 };
 
+static const float gain_tweek[7] = {
+    LEVEL_ONE,
+    LEVEL_ONE,
+    LEVEL_ONE,
+    LEVEL_ONE,
+    2,
+    3.16,
+    3.16
+};
+
 /**
  * Table for center mix levels
  * reference: Section 5.4.2.4 cmixlev
@@ -1111 +1121 @@
 
     /* apply scaling to coefficients (headroom, dynrng) */
     for(ch=1; ch<=s->channels; ch++) {
-        float gain = s->mul_bias / 4194304.0f;
+        float gain = s->mul_bias * gain_tweek[s->channels] / 4194304.0f;
         if(s->channel_mode == AC3_CHMODE_DUALMONO) {
             gain *= s->dynamic_range[ch-1];
         } else {