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

[Clément Bœsch]

On Mon, Sep 13, 2010 at 07:20:09AM +0200, Reimar Döffinger wrote:
> > [...]
> af_pan can only handle float. You should check it still works with an ao
> that can only handle int.

Mmh. The pan filter simply does not apply in this case, and there is this
message:

  [AO SDL] Samplerate: 44100Hz Channels: Stereo Format floatle
  [AO SDL] Unsupported audio format: 0x1d.

> Also the behaviour might be less surprising if you'd try to prepend
> af_pan first, but I admit that's likely to be quite messy...
> Anyway, printing a warning if audio_output_channels < s->last->data->nch
> might make sense, the behaviour of -channels 1 compared to -channels 2
> is not exactly consistent like this.

Is this related to the downmix?

> > [...]
> Much smaller/simpler as:
> static const char * const downmix_strs[AF_NCH] = {
> NULL, NULL, NULL,
> "pan=2:"/*Left:*/"0.6:0:"/*Right:*/"0:0.6:":0.4:0.4".
> ....
> };
> const char *str = downmix_strs[s->last->data->nch];
> if (str)
>     af_append(s, s->last, str);

Oh sure, it didn't crossed my mind. Does this look good to you with this
updated patch?

Regards,

-- 
Clément B.
-------------- next part --------------
Index: libaf/af.c
===================================================================
--- libaf/af.c	(revision 32219)
+++ 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 +362,25 @@
 }
 
 /**
+ * Automatic downmix to stereo in case the codec does not implement it.
+ */
+static void af_downmix(af_stream_t* s)
+{
+    static char * const downmix_strs[AF_NCH + 1] = {
+        [3] = "pan=2:" /*FL*/"0.6:0:" /*FR*/"0:0.6:"                                  /*FC*/"0.4:0.4",
+        [4] = "pan=2:" /*FL*/"0.6:0:" /*FR*/"0:0.6:" /*BL*/ "0.4:0:"  /*BR*/"0:0.4",
+        [5] = "pan=2:" /*FL*/"0.5:0:" /*FR*/"0:0.5:" /*BL*/ "0.2:0:"  /*BR*/"0:0.2:"  /*FC*/"0.3:0.3",
+        [6] = "pan=2:" /*FL*/"0.4:0:" /*FR*/"0:0.4:" /*BL*/ "0.2:0:"  /*BR*/"0:0.2:"  /*FC*/"0.3:0.3:"   /*LFE*/"0.1:0.1",
+        [7] = "pan=2:" /*FL*/"0.4:0:" /*FR*/"0:0.4:" /*BL*/ "0.2:0:"  /*BR*/"0:0.2:"  /*FC*/"0.3:0.3:"                     /*AL*/"0.1:0:" /*AR*/"0:0.1",
+        [8] = "pan=2:" /*FL*/"0.4:0:" /*FR*/"0:0.4:" /*BL*/ "0.15:0:" /*BR*/"0:0.15:" /*FC*/"0.25:0.25:" /*LFE*/"0.1:0.1:" /*AL*/"0.1:0:" /*AR*/"0:0.1",
+    };
+    char *af_pan_str = downmix_strs[s->last->data->nch];
+
+    if (af_pan_str)
+        af_append(s, s->last, af_pan_str);
+}
+
+/**
  * 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 +416,9 @@
 	return AF_ERROR;
     }
 
+    // Append a downmix pan filter to the end of the chain if needed
+    af_downmix(s);
+
     // Re init again just in case
     if(AF_OK != af_reinit(s,s->first))
       return AF_ERROR;