ao_coreaudio: fix device latency, share the code

ao_coreaudio (using AudioUnit) accounted only for part of the latency -
move the code in ao_coreaudio_exclusive to utils, and use that for the
AudioUnit code.

(There's still the question why CoreAudio and AudioUnit require you to
jump through hoops this much, but apparently that's how it is.)

audio/out/ao_coreaudio.c

@@ -56,12 +56,8 @@ static int64_t ca_get_hardware_latency(struct ao *ao) {
             &size);
     CHECK_CA_ERROR("cannot get audio unit latency");
 
-    uint32_t frames = 0;
-    err = CA_GET_O(p->device, kAudioDevicePropertyLatency, &frames);
-    CHECK_CA_ERROR("cannot get device latency");
-
     uint64_t audiounit_latency_us = audiounit_latency_sec * 1e6;
-    uint64_t device_latency_us    = ca_frames_to_us(ao, frames);
+    uint64_t device_latency_us    = ca_get_device_latency_us(ao, p->device);
 
     MP_VERBOSE(ao, "audiounit latency [us]: %lld\n", audiounit_latency_us);
     MP_VERBOSE(ao, "device latency [us]: %lld\n", device_latency_us);

audio/out/ao_coreaudio_exclusive.c

@@ -320,24 +320,7 @@ static int init(struct ao *ao)
         goto coreaudio_error;
     }
 
-    uint32_t latency_frames = 0;
-    uint32_t latency_properties[] = {
-        kAudioDevicePropertyLatency,
-        kAudioDevicePropertyBufferFrameSize,
-        kAudioDevicePropertySafetyOffset,
-    };
-    for (int n = 0; n < MP_ARRAY_SIZE(latency_properties); n++) {
-        uint32_t temp;
-        err = CA_GET_O(p->device, latency_properties[n], &temp);
-        CHECK_CA_WARN("cannot get device latency");
-        if (err == noErr) {
-            latency_frames += temp;
-            MP_VERBOSE(ao, "Latency property %s: %d frames\n",
-                       fourcc_repr(latency_properties[n]), (int)temp);
-        }
-    }
-
-    p->hw_latency_us = ca_frames_to_us(ao, latency_frames);
+    p->hw_latency_us = ca_get_device_latency_us(ao, p->device);
     MP_VERBOSE(ao, "base latency: %d microseconds\n", (int)p->hw_latency_us);
 
     err = enable_property_listener(ao, true);

audio/out/ao_coreaudio_utils.c

@@ -448,6 +448,28 @@ OSStatus ca_enable_mixing(struct ao *ao, AudioDeviceID device, bool changed)
     return noErr;
 }
 
+int64_t ca_get_device_latency_us(struct ao *ao, AudioDeviceID device)
+{
+    uint32_t latency_frames = 0;
+    uint32_t latency_properties[] = {
+        kAudioDevicePropertyLatency,
+        kAudioDevicePropertyBufferFrameSize,
+        kAudioDevicePropertySafetyOffset,
+    };
+    for (int n = 0; n < MP_ARRAY_SIZE(latency_properties); n++) {
+        uint32_t temp;
+        OSStatus err = CA_GET_O(device, latency_properties[n], &temp);
+        CHECK_CA_WARN("cannot get device latency");
+        if (err == noErr) {
+            latency_frames += temp;
+            MP_VERBOSE(ao, "Latency property %s: %d frames\n",
+                       fourcc_repr(latency_properties[n]), (int)temp);
+        }
+    }
+
+    return ca_frames_to_us(ao, latency_frames);
+}
+
 static OSStatus ca_change_format_listener(
     AudioObjectID object, uint32_t n_addresses,
     const AudioObjectPropertyAddress addresses[],

audio/out/ao_coreaudio_utils.h

@@ -74,6 +74,7 @@ OSStatus ca_lock_device(AudioDeviceID device, pid_t *pid);
 OSStatus ca_unlock_device(AudioDeviceID device, pid_t *pid);
 OSStatus ca_disable_mixing(struct ao *ao, AudioDeviceID device, bool *changed);
 OSStatus ca_enable_mixing(struct ao *ao, AudioDeviceID device, bool changed);
+int64_t ca_get_device_latency_us(struct ao *ao, AudioDeviceID device);
 bool ca_change_physical_format_sync(struct ao *ao, AudioStreamID stream,
                                     AudioStreamBasicDescription change_format);