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

[Clément Bœsch]

On Sat, Sep 11, 2010 at 07:44:18PM +0200, Reimar Döffinger wrote:
> On Sat, Sep 11, 2010 at 07:26:30PM +0200, Clément Bœsch wrote:
> > On Sat, Sep 11, 2010 at 06:44:58PM +0200, Reimar Döffinger wrote:
> > > On Sat, Sep 11, 2010 at 04:18:15PM +0200, Clément Bœsch wrote:
> > > > @@ -1665,7 +1732,7 @@
> > > >      if (!(initialized_flags & INITIALIZED_AO)) {
> > > >          current_module="af_preinit";
> > > >          ao_data.samplerate=force_srate;
> > > > -        ao_data.channels=0;
> > > > +        ao_data.channels=audio_output_channels;
> > > 
> > > Please test this very carefully, especially make sure that
> > > all kinds of mono/stereo files still work with -channels 6.
> > > I am for some reason quite convinced this was 0 for a good reason.
> > 
> > Oh you've right, sorry: If I play a stereo file, I get the sound in only
> > right and left while the current behaviour gives output to the 6 physical
> > channels with a stereo audio.
> > 
> > Well then I'm going to try something else, but if anyone has an idea how
> > it could be fixed please share…
> 
> Use
> ao_data.channels=-audio_output_channels;
> as initial value.
> The extend init_audio_filters to handle a negative channels values
> as "at most this many channels".
> For this, place your af_add code there.
> No promise it will work, but I expect in init_audio_filters you
> are most likely to have all the flexibility you need.

Thanks a lot for those information!

Instead of hacking the channels field, I just got it directly globally in
libaf/af.c

Maybe it's still not the right place but it seems to work:

- Basic stereo files use all my 6 physical channels
- 6_channel_ID.flac is downmixed to two channels by default and init is
  done like this: 48000Hz 2ch floatle
- 6_channel_ID.flac is not downmixed if -channels 6 is specified and init
  is done like this: 44100Hz 6ch s16le

It works for my case but I'm wondering about the format changement… maybe
you can enlight me about it.

Regards,

-- 
Clément B.
-------------- next part --------------
Index: libaf/af.c
===================================================================
--- libaf/af.c	(revision 32210)
+++ 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"
 
@@ -361,6 +362,74 @@
 }
 
 /**
+ * Automatic downmix to stereo in case the codec does not implement it.
+ */
+static void downmix_if_needed(af_stream_t* s)
+{
+    if (audio_output_channels != 2)
+        return;
+    switch (s->last->data->nch) {
+    case 8:
+        af_append(s, s->last, "pan=2:"
+                              "0.4:0:"      // Front left
+                              "0:0.4:"      // Front right
+                              "0.15:0:"     // Back left
+                              "0:0.15:"     // Back right
+                              "0.25:0.25:"  // Center
+                              "0.1:0.1:"    // LFE
+                              "0.1:0:"      // Auxiliary left
+                              "0:0.1"       // Auxiliary right
+        );
+        break;
+    case 7:
+        af_append(s, s->last, "pan=2:"
+                              "0.4:0:"      // Front left
+                              "0:0.4:"      // Front right
+                              "0.2:0:"      // Back left
+                              "0:0.2:"      // Back right
+                              "0.3:0.3:"    // Center
+                              "0.1:0:"      // Auxiliary left
+                              "0:0.1"       // Auxiliary right
+        );
+        break;
+    case 6:
+        af_append(s, s->last, "pan=2:"
+                              "0.4:0:"      // Front left
+                              "0:0.4:"      // Front right
+                              "0.2:0:"      // Back left
+                              "0:0.2:"      // Back right
+                              "0.3:0.3:"    // Center
+                              "0.1:0.1"     // LFE
+        );
+        break;
+    case 5:
+        af_append(s, s->last, "pan=2:"
+                              "0.5:0:"      // Front left
+                              "0:0.5:"      // Front right
+                              "0.2:0:"      // Back left
+                              "0:0.2:"      // Back right
+                              "0.3:0.3"     // Center
+        );
+        break;
+    case 4:
+        af_append(s, s->last, "pan=2:"
+                              "0.6:0:"      // Front left
+                              "0:0.6:"      // Front right
+                              "0.4:0:"      // Back left
+                              "0:0.4"       // Back right
+        );
+        break;
+    case 3:
+        af_append(s, s->last, "pan=2:"
+                              "0.6:0:"      // Left
+                              "0:0.6:"      // Right
+                              "0.4:0.4"     // Center
+        );
+        break;
+    }
+}
+
+/**
  * Extend the filter chain so we get the required output format at the end.
  * \return AF_ERROR on error, AF_OK if successful.
  */
@@ -396,6 +465,8 @@
 	return AF_ERROR;
     }
 
+    downmix_if_needed(s);
+
     // Re init again just in case
     if(AF_OK != af_reinit(s,s->first))
       return AF_ERROR;