ao_alsa: use new padding channels support

Sometimes, ALSA will return channel layouts with padded channels (NA
speakers). Use them instead of failing.

This still includes the old "braindeath" code to retry with a layout
without NA channels. This might be helpful for performance, and also the
padded channel layout string looks confusing.

To be fair, I have not encountered a case yet which would really need
this, and for which the old "braindeath" code did not fix it.

1 files changed, 26 insertions, 21 deletions

diff --git a/audio/out/ao_alsa.c b/audio/out/ao_alsa.c
index 82494717cf..e31e8012f8 100644
--- a/audio/out/ao_alsa.c
+++ b/audio/out/ao_alsa.c
@@ -252,6 +252,7 @@ static const int alsa_to_mp_channels[][2] = {
     {SND_CHMAP_TRR,     MP_SP(TBR)},
     {SND_CHMAP_TRC,     MP_SP(TBC)},
     {SND_CHMAP_MONO,    MP_SP(FC)},
+    {SND_CHMAP_NA,      MP_SPEAKER_ID_NA0},
     {SND_CHMAP_LAST,    MP_SPEAKER_ID_COUNT}
 };
 
@@ -282,9 +283,14 @@ static int mp_chmap_from_alsa(struct mp_chmap *dst, snd_pcm_chmap_t *src)
     if (src->channels > MP_NUM_CHANNELS)
         return -1;
 
+    int next_na = MP_SPEAKER_ID_NA0;
+
     dst->num = src->channels;
-    for (int c = 0; c < dst->num; c++)
+    for (int c = 0; c < dst->num; c++) {
         dst->speaker[c] = find_mp_channel(src->pos[c]);
+        if (dst->speaker[c] == MP_SPEAKER_ID_NA0)
+            dst->speaker[c] = next_na++;
+    }
 
     return 0;
 }
@@ -412,7 +418,7 @@ alsa_error: ;
 #define INIT_OK 0
 #define INIT_ERROR -1
 #define INIT_BRAINDEATH -2
-static int init_device(struct ao *ao)
+static int init_device(struct ao *ao, bool second_try)
 {
     struct priv *p = ao->priv;
     int err;
@@ -582,24 +588,14 @@ static int init_device(struct ao *ao)
         } else if (AF_FORMAT_IS_IEC61937(ao->format)) {
             MP_VERBOSE(ao, "using spdif passthrough; ignoring the channel map.\n");
         } else if (mp_chmap_is_valid(&chmap)) {
-            if (mp_chmap_equals(&chmap, &ao->channels)) {
-                MP_VERBOSE(ao, "which is what we requested.\n");
-            } else if (chmap.num == ao->channels.num) {
-                MP_VERBOSE(ao, "using the ALSA channel map.\n");
-                ao->channels = chmap;
-            } else {
-                MP_WARN(ao, "ALSA channel map conflicts with channel count!\n");
-            }
-        } else {
             // Is it one that contains NA channels?
-            struct mp_chmap chmap2 = {0};
-            for (int c = 0; c < alsa_chmap->channels; c++) {
-                int alsa_ch = alsa_chmap->pos[c];
-                if (alsa_ch != SND_CHMAP_NA)
-                    chmap2.speaker[chmap2.num++] = find_mp_channel(alsa_ch);
-            }
+            struct mp_chmap without_na = chmap;
+            mp_chmap_remove_na(&without_na);
 
-            if (mp_chmap_is_valid(&chmap2)) {
+            if (mp_chmap_is_valid(&without_na) &&
+                !mp_chmap_equals(&without_na, &chmap) &&
+                !second_try)
+            {
                 // Sometimes, ALSA will advertise certain chmaps, but it's not
                 // possible to set them. This can happen with dmix: as of
                 // alsa 1.0.28, dmix can do stereo only, but advertises the
@@ -616,10 +612,19 @@ static int init_device(struct ao *ao)
                 err = snd_pcm_close(p->alsa);
                 p->alsa = NULL;
                 CHECK_ALSA_ERROR("pcm close error");
-                ao->channels = chmap2;
+                ao->channels = without_na;
                 return INIT_BRAINDEATH;
             }
 
+            if (mp_chmap_equals(&chmap, &ao->channels)) {
+                MP_VERBOSE(ao, "which is what we requested.\n");
+            } else if (chmap.num == ao->channels.num) {
+                MP_VERBOSE(ao, "using the ALSA channel map.\n");
+                ao->channels = chmap;
+            } else {
+                MP_WARN(ao, "ALSA channel map conflicts with channel count!\n");
+            }
+        } else {
             MP_WARN(ao, "Got unknown channel map from ALSA.\n");
         }
 
@@ -690,9 +695,9 @@ static int init(struct ao *ao)
 
     MP_VERBOSE(ao, "using ALSA version: %s\n", snd_asoundlib_version());
 
-    int r = init_device(ao);
+    int r = init_device(ao, false);
     if (r == INIT_BRAINDEATH)
-        r = init_device(ao); // retry with normalized channel layout
+        r = init_device(ao, true); // retry with normalized channel layout
     return r == INIT_OK ? 0 : -1;
 }