Fix audio output latency measurement.

src/cubeb_audiounit.cpp

@@ -241,6 +241,7 @@ struct cubeb_stream {
   /* Latency requested by the user. */
   uint32_t latency_frames = 0;
   atomic<uint32_t> current_latency_frames{ 0 };
+  atomic<uint32_t> total_output_latency_frames { 0 };
   atomic<float> panning{ 0 };
   unique_ptr<cubeb_resampler, decltype(&cubeb_resampler_destroy)> resampler;
   /* This is true if a device change callback is currently running.  */
@@ -368,8 +369,10 @@ typedef UInt32 AudioObjectID;
 
 #define AudioGetCurrentHostTime mach_absolute_time
 
+#endif
+
 uint64_t
-AudioConvertHostTimeToNanos(uint64_t host_time)
+ConvertHostTimeToNanos(uint64_t host_time)
 {
   static struct mach_timebase_info timebase_info;
   static bool initialized = false;
@@ -385,7 +388,6 @@ AudioConvertHostTimeToNanos(uint64_t host_time)
   }
   return (uint64_t)answer;
 }
-#endif
 
 static void
 audiounit_increment_active_streams(cubeb * ctx)
@@ -583,6 +585,15 @@ audiounit_output_callback(void * user_ptr,
 
   cubeb_stream * stm = static_cast<cubeb_stream *>(user_ptr);
 
+  uint64_t now = ConvertHostTimeToNanos(mach_absolute_time());
+  uint64_t audio_output_time = ConvertHostTimeToNanos(tstamp->mHostTime);
+  uint64_t output_latency_ns = audio_output_time - now;
+
+  const int ns2s = 1e9;
+  // The total output latency is the timestamp difference + the stream latency +
+  // the hardware latency.
+  stm->total_output_latency_frames = output_latency_ns * stm->output_hw_rate / ns2s + stm->current_latency_frames;
+
   ALOGV("(%p) output: buffers %u, size %u, channels %u, frames %u, total input frames %lu.",
         stm,
         (unsigned int) outBufferList->mNumberBuffers,
@@ -2973,7 +2984,7 @@ audiounit_stream_get_latency(cubeb_stream * stm, uint32_t * latency)
   //TODO
   return CUBEB_ERROR_NOT_SUPPORTED;
 #else
-  *latency = stm->current_latency_frames;
+  *latency = stm->total_output_latency_frames;
   return CUBEB_OK;
 #endif
 }