ao_coreaudio: add support for hotplug notifications

This commit adds notifications for hot plugging of devices. It also extends
the old behaviour of the `audio-out-detected-device` property which is now
backed by the hotplugging code. This allows clients to be notified when the
actual audio output device changes.

Maybe hotplugging should be supported for ao_coreaudio_exclusive too, but it's
device selection code is a bit fragile.

TOOLS/lua/audio-hotplug-test.lua

@@ -6,3 +6,8 @@ mp.observe_property("audio-device-list", "native", function(name, val)
         print("  - '" .. e.name .. "' (" .. e.description .. ")")
     end
 end)
+
+mp.observe_property("audio-out-detected-device", "native", function(name, val)
+    print("Detected audio device changed:")
+    print("  - '" .. val)
+end)

audio/out/ao.c

@@ -450,11 +450,6 @@ bool ao_untimed(struct ao *ao)
     return ao->untimed;
 }
 
-const char *ao_get_detected_device(struct ao *ao)
-{
-    return ao->detected_device;
-}
-
 // ---
 
 struct ao_hotplug {
@@ -502,6 +497,11 @@ bool ao_hotplug_check_update(struct ao_hotplug *hp)
     return false;
 }
 
+const char *ao_hotplug_get_detected_device(struct ao_hotplug *hp)
+{
+    return hp->ao->detected_device;
+}
+
 // The return value is valid until the next call to this API.
 struct ao_device_list *ao_hotplug_get_device_list(struct ao_hotplug *hp)
 {

audio/out/ao.h

@@ -80,7 +80,6 @@ void ao_uninit(struct ao *ao);
 void ao_get_format(struct ao *ao, struct mp_audio *format);
 const char *ao_get_name(struct ao *ao);
 const char *ao_get_description(struct ao *ao);
-const char *ao_get_detected_device(struct ao *ao);
 bool ao_untimed(struct ao *ao);
 int ao_play(struct ao *ao, void **data, int samples, int flags);
 int ao_control(struct ao *ao, enum aocontrol cmd, void *arg);
@@ -100,6 +99,7 @@ struct ao_hotplug *ao_hotplug_create(struct mpv_global *global,
                                      struct input_ctx *input_ctx);
 void ao_hotplug_destroy(struct ao_hotplug *hp);
 bool ao_hotplug_check_update(struct ao_hotplug *hp);
+const char *ao_hotplug_get_detected_device(struct ao_hotplug *hp);
 struct ao_device_list *ao_hotplug_get_device_list(struct ao_hotplug *hp);
 
 void ao_print_devices(struct mpv_global *global, struct mp_log *log);

audio/out/ao_coreaudio.c

@@ -143,14 +143,7 @@ static int control(struct ao *ao, enum aocontrol cmd, void *arg)
 static bool init_chmap(struct ao *ao);
 static bool init_audiounit(struct ao *ao, AudioStreamBasicDescription asbd);
 
-static int init(struct ao *ao)
-{
-    if (AF_FORMAT_IS_IEC61937(ao->format)) {
-        MP_WARN(ao, "detected IEC61937, redirecting to coreaudio_exclusive\n");
-        ao->redirect = "coreaudio_exclusive";
-        return CONTROL_ERROR;
-    }
-
+static bool reinit_device(struct ao *ao) {
     struct priv *p = ao->priv;
 
     OSStatus err = ca_select_device(ao, ao->device, &p->device);
@@ -161,6 +154,23 @@ static int init(struct ao *ao)
     CHECK_CA_ERROR("failed to get device UID");
     ao->detected_device = talloc_steal(ao, uid);
 
+    return true;
+
+coreaudio_error:
+    return false;
+}
+
+static int init(struct ao *ao)
+{
+    if (AF_FORMAT_IS_IEC61937(ao->format)) {
+        MP_WARN(ao, "detected IEC61937, redirecting to coreaudio_exclusive\n");
+        ao->redirect = "coreaudio_exclusive";
+        return CONTROL_ERROR;
+    }
+
+    if (!reinit_device(ao))
+        goto coreaudio_error;
+
     if (!init_chmap(ao))
         goto coreaudio_error;
 
@@ -361,6 +371,67 @@ static void uninit(struct ao *ao)
     AudioComponentInstanceDispose(p->audio_unit);
 }
 
+static OSStatus hotplug_cb(AudioObjectID id, UInt32 naddr,
+                           const AudioObjectPropertyAddress addr[],
+                           void *ctx) {
+    reinit_device(ctx);
+    ao_hotplug_event(ctx);
+    return noErr;
+}
+
+static uint32_t hotplug_properties[] = {
+    kAudioHardwarePropertyDevices,
+    kAudioHardwarePropertyDefaultOutputDevice
+};
+
+static int hotplug_init(struct ao *ao)
+{
+    if (!reinit_device(ao))
+        goto coreaudio_error;
+
+    OSStatus err = noErr;
+    for (int i = 0; i < MP_ARRAY_SIZE(hotplug_properties); i++) {
+        AudioObjectPropertyAddress addr = {
+            hotplug_properties[i],
+            kAudioObjectPropertyScopeGlobal,
+            kAudioObjectPropertyElementMaster
+        };
+        err = AudioObjectAddPropertyListener(
+            kAudioObjectSystemObject, &addr, hotplug_cb, (void *)ao);
+        if (err != noErr) {
+            char *c1 = fourcc_repr(ao, hotplug_properties[i]);
+            char *c2 = fourcc_repr(ao, err);
+            MP_ERR(ao, "failed to set device listener %s (%s)", c1, c2);
+            goto coreaudio_error;
+        }
+    }
+
+    return 0;
+
+coreaudio_error:
+    return -1;
+}
+
+static void hotplug_uninit(struct ao *ao)
+{
+    OSStatus err = noErr;
+    for (int i = 0; i < MP_ARRAY_SIZE(hotplug_properties); i++) {
+        AudioObjectPropertyAddress addr = {
+            hotplug_properties[i],
+            kAudioObjectPropertyScopeGlobal,
+            kAudioObjectPropertyElementMaster
+        };
+        err = AudioObjectRemovePropertyListener(
+            kAudioObjectSystemObject, &addr, hotplug_cb, (void *)ao);
+        if (err != noErr) {
+            char *c1 = fourcc_repr(ao, hotplug_properties[i]);
+            char *c2 = fourcc_repr(ao, err);
+            MP_ERR(ao, "failed to set device listener %s (%s)", c1, c2);
+        }
+    }
+}
+
+
 // Channel Mapping functions
 static const int speaker_map[][2] = {
     { kAudioChannelLabel_Left,                 MP_SPEAKER_ID_FL   },
@@ -513,13 +584,15 @@ coreaudio_error:
 #define OPT_BASE_STRUCT struct priv
 
 const struct ao_driver audio_out_coreaudio = {
-    .description = "CoreAudio AudioUnit",
-    .name      = "coreaudio",
-    .uninit    = uninit,
-    .init      = init,
-    .control   = control,
-    .pause     = stop,
-    .resume    = start,
-    .list_devs = ca_get_device_list,
-    .priv_size = sizeof(struct priv),
+    .description    = "CoreAudio AudioUnit",
+    .name           = "coreaudio",
+    .uninit         = uninit,
+    .init           = init,
+    .control        = control,
+    .pause          = stop,
+    .resume         = start,
+    .hotplug_init   = hotplug_init,
+    .hotplug_uninit = hotplug_uninit,
+    .list_devs      = ca_get_device_list,
+    .priv_size      = sizeof(struct priv),
 };

player/command.c

@@ -1578,10 +1578,12 @@ static int mp_property_ao(void *ctx, struct m_property *p, int action, void *arg
 static int mp_property_ao_detected_device(void *ctx,struct m_property *prop,
                                           int action, void *arg)
 {
-    MPContext *mpctx = ctx;
+    struct MPContext *mpctx = ctx;
+    struct command_ctx *cmd = mpctx->command_ctx;
     if (!mpctx->ao)
         return M_PROPERTY_UNAVAILABLE;
-    return m_property_strdup_ro(action, arg, ao_get_detected_device(mpctx->ao));
+    const char *d = ao_hotplug_get_detected_device(cmd->hotplug);
+    return m_property_strdup_ro(action, arg, d);
 }
 
 /// Audio delay (RW)
@@ -3524,7 +3526,7 @@ static const char *const *const mp_event_property_change[] = {
       "detected-hwdec"),
     E(MPV_EVENT_AUDIO_RECONFIG, "audio-format", "audio-codec", "audio-bitrate",
       "samplerate", "channels", "audio", "volume", "mute", "balance",
-      "volume-restore-data", "current-ao", "audio-out-detected-device"),
+      "volume-restore-data", "current-ao"),
     E(MPV_EVENT_SEEK, "seeking", "core-idle"),
     E(MPV_EVENT_PLAYBACK_RESTART, "seeking", "core-idle"),
     E(MPV_EVENT_METADATA_UPDATE, "metadata", "filtered-metadata"),
@@ -3534,6 +3536,7 @@ static const char *const *const mp_event_property_change[] = {
     E(MP_EVENT_WIN_RESIZE, "window-scale"),
     E(MP_EVENT_WIN_STATE, "window-minimized", "display-names"),
     E(MP_EVENT_AUDIO_DEVICES, "audio-device-list"),
+    E(MP_EVENT_DETECTED_AUDIO_DEVICE, "audio-out-detected-device"),
 };
 #undef E
 
@@ -4875,8 +4878,10 @@ static void command_event(struct MPContext *mpctx, int event, void *arg)
 
     // This is a bit messy: ao_hotplug wakes up the player, and then we have
     // to recheck the state. Then the client(s) will read the property.
-    if (ctx->hotplug && ao_hotplug_check_update(ctx->hotplug))
+    if (ctx->hotplug && ao_hotplug_check_update(ctx->hotplug)) {
         mp_notify_property(mpctx, "audio-device-list");
+        mp_notify_property(mpctx, "audio-out-detected-device");
+    }
 }
 
 void mp_notify(struct MPContext *mpctx, int event, void *arg)

player/command.h

@@ -48,6 +48,7 @@ enum {
     MP_EVENT_WIN_RESIZE,
     MP_EVENT_WIN_STATE,
     MP_EVENT_AUDIO_DEVICES,
+    MP_EVENT_DETECTED_AUDIO_DEVICE,
 };
 
 bool mp_hook_test_completion(struct MPContext *mpctx, char *type);