ao_coreaudio: use device UID instead of ID for selection

Previously we let the user use the audio device ID, but this is not persistent
and can change when plugging in new devices. That of course made it quite
worthless for storing it as a user setting for GUIs, or for user scripts.

In theory getting the kAudioDevicePropertyDeviceUID can fail but it doesn't
on any of my devices, so I'm leaving the error reporting quite high and see if
someone complains.

audio/out/ao_coreaudio.c

@@ -156,7 +156,10 @@ static int init(struct ao *ao)
     OSStatus err = ca_select_device(ao, ao->device, &p->device);
     CHECK_CA_ERROR("failed to select device");
 
-    ao->detected_device = talloc_asprintf(ao, "%d", p->device);
+    char *uid;
+    err = CA_GET_STR(p->device, kAudioDevicePropertyDeviceUID, &uid);
+    CHECK_CA_ERROR("failed to get device UID");
+    ao->detected_device = talloc_steal(ao, uid);
 
     if (!init_chmap(ao))
         goto coreaudio_error;

audio/out/ao_coreaudio_properties.c

@@ -83,12 +83,7 @@ OSStatus ca_get_str(AudioObjectID id, ca_scope scope, ca_sel selector,
         ca_get(id, scope, selector, sizeof(CFStringRef), (void **)&string);
     CHECK_CA_ERROR_SILENT_L(coreaudio_error);
 
-    CFIndex size =
-        CFStringGetMaximumSizeForEncoding(
-            CFStringGetLength(string), CA_CFSTR_ENCODING) + 1;
-
-    *data = talloc_zero_size(NULL, size);
-    CFStringGetCString(string, *data, size, CA_CFSTR_ENCODING);
+    *data = cfstr_get_cstr(string);
     CFRelease(string);
 coreaudio_error:
     return err;

audio/out/ao_coreaudio_utils.c

@@ -28,6 +28,21 @@
 #include "osdep/endian.h"
 #include "audio/format.h"
 
+CFStringRef cfstr_from_cstr(char *str)
+{
+    return CFStringCreateWithCString(NULL, str, CA_CFSTR_ENCODING);
+}
+
+char *cfstr_get_cstr(CFStringRef cfstr)
+{
+    CFIndex size =
+        CFStringGetMaximumSizeForEncoding(
+            CFStringGetLength(cfstr), CA_CFSTR_ENCODING) + 1;
+    char *buffer = talloc_zero_size(NULL, size);
+    CFStringGetCString(cfstr, buffer, size, CA_CFSTR_ENCODING);
+    return buffer;
+}
+
 static bool ca_is_output_device(struct ao *ao, AudioDeviceID dev)
 {
     size_t n_buffers;
@@ -49,9 +64,9 @@ void ca_get_device_list(struct ao *ao, struct ao_device_list *list)
     for (int i = 0; i < n_devs; i++) {
         if (!ca_is_output_device(ao, devs[i]))
             continue;
-        char name[32];
+        char *name;
         char *desc;
-        sprintf(name, "%d", devs[i]);
+        err = CA_GET_STR(devs[i], kAudioDevicePropertyDeviceUID, &name);
         err = CA_GET_STR(devs[i], kAudioObjectPropertyName, &desc);
         if (err != noErr)
             desc = "Unknown";
@@ -65,21 +80,32 @@ coreaudio_error:
 OSStatus ca_select_device(struct ao *ao, char* name, AudioDeviceID *device)
 {
     OSStatus err = noErr;
-    errno = 0;
-    int selection = name && name[0] ? strtol(name, (char **)NULL, 10) : -1;
-    if (errno == EINVAL || errno == ERANGE) {
-        selection = -1;
-        MP_WARN(ao, "device identifier '%s' is invalid\n", name);
-    }
-    *device = 0;
-    if (selection < 0) {
+    *device = kAudioObjectUnknown;
+
+    if (name) {
+        CFStringRef uid = cfstr_from_cstr(name);
+        AudioValueTranslation v = (AudioValueTranslation) {
+            .mInputData = &uid,
+            .mInputDataSize = sizeof(CFStringRef),
+            .mOutputData = device,
+            .mOutputDataSize = sizeof(*device),
+        };
+        uint32_t size = sizeof(AudioValueTranslation);
+        AudioObjectPropertyAddress p_addr = (AudioObjectPropertyAddress) {
+            .mSelector = kAudioHardwarePropertyDeviceForUID,
+            .mScope    = kAudioObjectPropertyScopeGlobal,
+            .mElement  = kAudioObjectPropertyElementMaster,
+        };
+        err = AudioObjectGetPropertyData(
+            kAudioObjectSystemObject, &p_addr, 0, 0, &size, &v);
+        CFRelease(uid);
+        CHECK_CA_ERROR("unable to query for device UID");
+    } else {
         // device not set by user, get the default one
         err = CA_GET(kAudioObjectSystemObject,
                      kAudioHardwarePropertyDefaultOutputDevice,
                      device);
         CHECK_CA_ERROR("could not get default audio device");
-    } else {
-        *device = selection;
     }
 
     if (mp_msg_test(ao->log, MSGL_V)) {

audio/out/ao_coreaudio_utils.h

@@ -28,6 +28,9 @@
 
 #define CA_CFSTR_ENCODING kCFStringEncodingASCII
 
+CFStringRef cfstr_from_cstr(char *str);
+char *cfstr_get_cstr(CFStringRef cfstr);
+
 char *fourcc_repr(void *talloc_ctx, uint32_t code);
 bool check_ca_st(struct ao *ao, int level, OSStatus code, const char *message);