[MPlayer-dev-eng] [PATCH] Automatic downmix

[Clément Bœsch]

On Tue, Sep 14, 2010 at 08:29:07PM +0200, Clément Bœsch wrote:
> So here is a new version of the patch.

And here is a new one with a small design changement you may prefer.

Regards,

-- 
Clément B.
-------------- next part --------------
Index: libaf/af.c
===================================================================
--- libaf/af.c	(revision 32278)
+++ libaf/af.c	(working copy)
@@ -21,6 +21,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include "osdep/strsep.h"
+#include "libmpcodecs/dec_audio.h"
 
 #include "af.h"
 
@@ -412,6 +413,24 @@
     return AF_OK;
 }
 
+/**
+ * Automatic downmix to stereo in case the codec does not implement it.
+ */
+static af_instance_t *af_downmix(af_stream_t* s)
+{
+    static char * const downmix_strs[AF_NCH + 1] = {
+        /*                FL       FR       RL       RR          FC          LF         AL      AR */
+        [3] = "pan=2:" "0.6:0:" "0:0.6:"                     "0.4:0.4",
+        [4] = "pan=2:" "0.6:0:" "0:0.6:" "0.4:0:"  "0:0.4",
+        [5] = "pan=2:" "0.5:0:" "0:0.5:" "0.2:0:"  "0:0.2:"  "0.3:0.3",
+        [6] = "pan=2:" "0.4:0:" "0:0.4:" "0.2:0:"  "0:0.2:"  "0.3:0.3:"   "0.1:0.1",
+        [7] = "pan=2:" "0.4:0:" "0:0.4:" "0.2:0:"  "0:0.2:"  "0.3:0.3:"              "0.1:0:" "0:0.1",
+        [8] = "pan=2:" "0.4:0:" "0:0.4:" "0.15:0:" "0:0.15:" "0.25:0.25:" "0.1:0.1:" "0.1:0:" "0:0.1",
+    };
+    char *af_pan_str = downmix_strs[s->last->data->nch];
+    return af_pan_str ? af_append(s, s->last, af_pan_str) : NULL;
+}
+
 /* Initialize the stream "s". This function creates a new filter list
    if necessary according to the values set in input and output. Input
    and output should contain the format of the current movie and the
@@ -460,6 +479,13 @@
     if (!af_append(s,s->first,"dummy") || AF_OK != af_reinit(s,s->first))
       return -1;
 
+  // Append a downmix pan filter to the end of the chain if needed
+  if (audio_output_channels == 2) {
+    af_instance_t *filter = af_downmix(s);
+    if (filter && AF_OK != af_reinit(s, filter))
+      return -1;
+  }
+
   // Check output format
   if((AF_INIT_TYPE_MASK & s->cfg.force) != AF_INIT_FORCE){
     af_instance_t* af = NULL; // New filter