ALSA: still use VLC configuration to determine available speakers

The ALSA channels maps only indicate the order(s) of channels supported
by the audio adapter. They do not imply that all channels are actually
physically wired.

modules/audio_output/alsa.c

@@ -145,24 +145,6 @@ static void DumpDeviceStatus (vlc_object_t *obj, snd_pcm_t *pcm)
 }
 #define DumpDeviceStatus(o, p) DumpDeviceStatus(VLC_OBJECT(o), p)
 
-static unsigned SetupChannelsUnknown (vlc_object_t *obj,
-                                      uint16_t *restrict mask)
-{
-    uint16_t map = var_InheritInteger (obj, "alsa-audio-channels");
-    uint16_t chans = *mask & map;
-
-    if (unlikely(chans == 0)) /* WTH? */
-        chans = AOUT_CHANS_STEREO;
-
-    if (popcount (chans) < popcount (*mask))
-        msg_Dbg (obj, "downmixing from %u to %u channels",
-                 popcount (*mask), popcount (chans));
-    else
-        msg_Dbg (obj, "keeping %u channels", popcount (chans));
-    *mask = chans;
-    return 0;
-}
-
 #if (SND_LIB_VERSION >= 0x01001B)
 static const uint16_t vlc_chans[] = {
     [SND_CHMAP_MONO] = AOUT_CHAN_CENTER,
@@ -228,18 +210,17 @@ static unsigned SetupChannelsFixed(const snd_pcm_chmap_t *restrict map,
  * Negotiate channels mapping.
  */
 static unsigned SetupChannels (vlc_object_t *obj, snd_pcm_t *pcm,
-                                uint16_t *restrict mask, uint8_t *restrict tab)
+                               uint16_t *restrict mask, uint8_t *restrict tab)
 {
     snd_pcm_chmap_query_t **maps = snd_pcm_query_chmaps (pcm);
     if (maps == NULL)
-    {   /* Fallback to manual configuration */
+    {   /* Fallback to default order if unknown */
         msg_Dbg(obj, "channels map not provided");
-        return SetupChannelsUnknown (obj, mask);
+        return 0;
     }
 
     /* Find most appropriate available channels map */
-    unsigned best_offset;
-    unsigned best_score = 0;
+    unsigned best_offset, best_score = 0, to_reorder = 0;
 
     for (snd_pcm_chmap_query_t *const *p = maps; *p != NULL; p++)
     {
@@ -271,8 +252,7 @@ static unsigned SetupChannels (vlc_object_t *obj, snd_pcm_t *pcm,
     if (best_score == 0)
     {
         msg_Err (obj, "cannot find supported channels map");
-        snd_pcm_free_chmaps (maps);
-        return SetupChannelsUnknown (obj, mask);
+        goto out;
     }
 
     const snd_pcm_chmap_t *map = &maps[best_offset]->map;
@@ -280,17 +260,16 @@ static unsigned SetupChannels (vlc_object_t *obj, snd_pcm_t *pcm,
              maps[best_offset]->type, map->channels);
 
     /* Setup channels map */
-    unsigned to_reorder = SetupChannelsFixed(map, mask, tab);
+    to_reorder = SetupChannelsFixed(map, mask, tab);
 
     /* TODO: avoid reordering for PAIRED and VAR types */
     //snd_pcm_set_chmap (pcm, ...)
-
+out:
     snd_pcm_free_chmaps (maps);
     return to_reorder;
 }
 #else /* (SND_LIB_VERSION < 0x01001B) */
-# define SetupChannels(obj, pcm, mask, tab) \
-         SetupChannelsUnknown(obj, mask)
+# define SetupChannels(obj, pcm, mask, tab) (0)
 #endif
 
 static int TimeGet (audio_output_t *aout, mtime_t *);
@@ -457,16 +436,19 @@ static int Start (audio_output_t *aout, audio_sample_format_t *restrict fmt)
     unsigned channels;
     if (!spdif)
     {
-        sys->chans_to_reorder = SetupChannels (VLC_OBJECT(aout), pcm,
-                                  &fmt->i_physical_channels, sys->chans_table);
-        channels = popcount (fmt->i_physical_channels);
+        uint16_t map = var_InheritInteger (aout, "alsa-audio-channels");
+
+        sys->chans_to_reorder = SetupChannels (VLC_OBJECT(aout), pcm, &map,
+                                               sys->chans_table);
+        fmt->i_physical_channels = map;
+        fmt->i_original_channels = map;
+        channels = popcount (map);
     }
     else
     {
         sys->chans_to_reorder = 0;
         channels = 2;
     }
-    fmt->i_original_channels = fmt->i_physical_channels;
 
     /* By default, ALSA plug will pad missing channels with zeroes, which is
      * usually fine. However, it will also discard extraneous channels, which