ao_coreaudio_exclusive: fallback to stereo on unknown channel layouts

This is intended for the case when CoreAudio returns only unknown
channel layouts, or no channel layout matches the number of channels the
CoreAudio device forces. Assume that outputting stereo or mono to the
first channels is safe, and that it's better than outputting nothing.

It's notable that XBMC/kodi falls back to a static channel layout in
this case. For some messed up reason, the layout it uses happens to
match with the channel order in ALSA's/mpv's "7.1(alsa)" layout.

1 files changed, 10 insertions, 1 deletions

diff --git a/audio/out/ao_coreaudio_chmap.c b/audio/out/ao_coreaudio_chmap.c
index d5a38d325e..bdd625ff53 100644
--- a/audio/out/ao_coreaudio_chmap.c
+++ b/audio/out/ao_coreaudio_chmap.c
@@ -281,6 +281,7 @@ void ca_get_active_chmap(struct ao *ao, AudioDeviceID device, int channel_count,
     struct mp_chmap_sel chmap_sel = {0};
     ca_retrieve_layouts(ao, &chmap_sel, device);
 
+    // Use any exact match.
     for (int n = 0; n < chmap_sel.num_chmaps; n++) {
         if (chmap_sel.chmaps[n].num == channel_count) {
             MP_VERBOSE(ao, "mismatching channels - fallback #%d\n", n);
@@ -289,5 +290,13 @@ void ca_get_active_chmap(struct ao *ao, AudioDeviceID device, int channel_count,
         }
     }
 
-    out_map->num = 0;
+    // Fall back to stereo or mono, and fill the rest with silence. (We don't
+    // know what the device expects. We could use a larger default layout here,
+    // but let's not.)
+    mp_chmap_from_channels(out_map, MPMIN(2, channel_count));
+    out_map->num = channel_count;
+    for (int n = 2; n < out_map->num; n++)
+        out_map->speaker[n] = MP_SPEAKER_ID_NA;
+    MP_WARN(ao, "mismatching channels - falling back to %s\n",
+            mp_chmap_to_str(out_map));
 }