[remoting host][mac] Add silence detection for AudioCapturerMac

This CL adds silence detection logic for AudioCapturerMac so that it
doesn't send empty audio packets and waste the bandwidth.

Bug: 1161363
Change-Id: I891355b0ca31fb12eb40feb4f9b189645d36193c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2618473Reviewed-by: Joe Downing <joedow@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841737}

remoting/host/audio_capturer_mac.cc

@@ -33,6 +33,7 @@ constexpr int kBytesPerFrame = kBytesPerChannel * kChannelsPerFrame;
 constexpr float kBufferTimeDurationSec = 0.01f;  // 10ms
 constexpr size_t kBufferByteSize =
     kSampleRate * kBytesPerFrame * kBufferTimeDurationSec;
+constexpr int kAudioSilenceThreshold = 0;
 
 // Total delay: kBufferTimeDurationSec * kNumberBuffers
 constexpr int kNumberBuffers = 2;
@@ -94,7 +95,8 @@ AudioCapturerInstanceSet* AudioCapturerInstanceSet::Get() {
 }  // namespace
 
 AudioCapturerMac::AudioCapturerMac(const std::string& audio_device_uid)
-    : audio_device_uid_(audio_device_uid) {
+    : audio_device_uid_(audio_device_uid),
+      silence_detector_(kAudioSilenceThreshold) {
   DETACH_FROM_SEQUENCE(sequence_checker_);
   DCHECK(!audio_device_uid.empty());
 
@@ -170,8 +172,9 @@ void AudioCapturerMac::HandleInputBuffer(AudioQueueRef aq,
   DCHECK_EQ(input_queue_, aq);
   DCHECK(callback_);
 
-  // TODO(yuweih): Add silence detection and drop empty packets.
-
+  if (!silence_detector_.IsSilence(
+          reinterpret_cast<const int16_t*>(buffer->mAudioData),
+          buffer->mAudioDataByteSize / sizeof(int16_t) / kChannelsPerFrame)) {
     auto packet = std::make_unique<AudioPacket>();
     packet->add_data(buffer->mAudioData, buffer->mAudioDataByteSize);
     packet->set_encoding(AudioPacket::ENCODING_RAW);
@@ -179,6 +182,7 @@ void AudioCapturerMac::HandleInputBuffer(AudioQueueRef aq,
     packet->set_bytes_per_sample(AudioPacket::BYTES_PER_SAMPLE_2);
     packet->set_channels(AudioPacket::CHANNELS_STEREO);
     callback_.Run(std::move(packet));
+  }
 
   // Recycle the buffer.
   // Only the first 2 params are needed for recording.
@@ -242,6 +246,8 @@ bool AudioCapturerMac::StartInputQueue() {
   }
   is_started_ = true;
 
+  silence_detector_.Reset(kSampleRate, kChannelsPerFrame);
+
   return true;
 }
 

remoting/host/audio_capturer_mac.h

@@ -15,6 +15,7 @@
 #include "base/sequence_checker.h"
 #include "base/sequenced_task_runner.h"
 #include "remoting/host/audio_capturer.h"
+#include "remoting/host/audio_silence_detector.h"
 
 namespace remoting {
 
@@ -57,6 +58,7 @@ class AudioCapturerMac : public AudioCapturer {
   std::string audio_device_uid_;
 
   AudioStreamBasicDescription stream_description_;
+  AudioSilenceDetector silence_detector_;
   PacketCapturedCallback callback_;
   AudioQueueRef input_queue_ = nullptr;
   bool is_started_ = false;