Check the mic volume only periodically on Mac.

Ask the OS for the mic volume every 1 second rather than with every 10
ms chunk. The previous behavior was consuming ~2% of the CPU load of
a voice engine call, and is now negligible.

This is consistent with the webrtc Windows Core Audio implementation,
as well as the Chromium Mac implementation:
https://code.google.com/p/chromium/codesearch#chromium/src/media/audio/agc_audio_stream.h

TEST=voe_cmd_test with AGC continues to work well on Mac.

Review URL: https://codereview.webrtc.org/1564223002

Cr-Commit-Position: refs/heads/master@{#11182}

2 files changed, 25 insertions, 9 deletions

diff --git a/webrtc/modules/audio_device/mac/audio_device_mac.cc b/webrtc/modules/audio_device/mac/audio_device_mac.cc
index 3449188dc0..d963f2b7f2 100644
--- a/webrtc/modules/audio_device/mac/audio_device_mac.cc
+++ b/webrtc/modules/audio_device/mac/audio_device_mac.cc
@@ -149,7 +149,8 @@ AudioDeviceMac::AudioDeviceMac(const int32_t id) :
     _paRenderBuffer(NULL),
     _captureBufSizeSamples(0),
     _renderBufSizeSamples(0),
-    prev_key_state_()
+    prev_key_state_(),
+    get_mic_volume_counter_ms_(0)
 {
     WEBRTC_TRACE(kTraceMemory, kTraceAudioDevice, id,
                  "%s created", __FUNCTION__);
@@ -379,6 +380,8 @@ int32_t AudioDeviceMac::Init()
     _recWarning = 0;
     _recError = 0;
 
+    get_mic_volume_counter_ms_ = 0;
+
     _initialized = true;
 
     return 0;
@@ -3181,12 +3184,17 @@ bool AudioDeviceMac::CaptureWorkerThread()
 
         if (AGC())
         {
-            // store current mic level in the audio buffer if AGC is enabled
-            if (MicrophoneVolume(currentMicLevel) == 0)
-            {
-                // this call does not affect the actual microphone volume
-                _ptrAudioBuffer->SetCurrentMicLevel(currentMicLevel);
+            // Use mod to ensure we check the volume on the first pass.
+            if (get_mic_volume_counter_ms_ % kGetMicVolumeIntervalMs == 0) {
+                get_mic_volume_counter_ms_ = 0;
+                // store current mic level in the audio buffer if AGC is enabled
+                if (MicrophoneVolume(currentMicLevel) == 0)
+                {
+                    // this call does not affect the actual microphone volume
+                    _ptrAudioBuffer->SetCurrentMicLevel(currentMicLevel);
+                }
             }
+            get_mic_volume_counter_ms_ += kBufferSizeMs;
         }
 
         _ptrAudioBuffer->SetVQEData(msecOnPlaySide, msecOnRecordSide, 0);
diff --git a/webrtc/modules/audio_device/mac/audio_device_mac.h b/webrtc/modules/audio_device/mac/audio_device_mac.h
index bb900e07aa..849e74ce45 100644
--- a/webrtc/modules/audio_device/mac/audio_device_mac.h
+++ b/webrtc/modules/audio_device/mac/audio_device_mac.h
@@ -38,20 +38,26 @@ const uint32_t N_REC_CHANNELS = 1; // default is mono recording
 const uint32_t N_PLAY_CHANNELS = 2; // default is stereo playout
 const uint32_t N_DEVICE_CHANNELS = 64;
 
-const uint32_t ENGINE_REC_BUF_SIZE_IN_SAMPLES = (N_REC_SAMPLES_PER_SEC / 100);
-const uint32_t ENGINE_PLAY_BUF_SIZE_IN_SAMPLES = (N_PLAY_SAMPLES_PER_SEC / 100);
+const int kBufferSizeMs = 10;
+
+const uint32_t ENGINE_REC_BUF_SIZE_IN_SAMPLES =
+    N_REC_SAMPLES_PER_SEC * kBufferSizeMs / 1000;
+const uint32_t ENGINE_PLAY_BUF_SIZE_IN_SAMPLES =
+    N_PLAY_SAMPLES_PER_SEC * kBufferSizeMs / 1000;
 
 const int N_BLOCKS_IO = 2;
 const int N_BUFFERS_IN = 2;  // Must be at least N_BLOCKS_IO.
 const int N_BUFFERS_OUT = 3;  // Must be at least N_BLOCKS_IO.
 
-const uint32_t TIMER_PERIOD_MS = (2 * 10 * N_BLOCKS_IO * 1000000);
+const uint32_t TIMER_PERIOD_MS = 2 * 10 * N_BLOCKS_IO * 1000000;
 
 const uint32_t REC_BUF_SIZE_IN_SAMPLES =
     ENGINE_REC_BUF_SIZE_IN_SAMPLES * N_DEVICE_CHANNELS * N_BUFFERS_IN;
 const uint32_t PLAY_BUF_SIZE_IN_SAMPLES =
     ENGINE_PLAY_BUF_SIZE_IN_SAMPLES * N_PLAY_CHANNELS * N_BUFFERS_OUT;
 
+const int kGetMicVolumeIntervalMs = 1000;
+
 class AudioDeviceMac: public AudioDeviceGeneric
 {
 public:
@@ -372,6 +378,8 @@ private:
     // Typing detection
     // 0x5c is key "9", after that comes function keys.
     bool prev_key_state_[0x5d];
+
+    int get_mic_volume_counter_ms_;
 };
 
 }  // namespace webrtc