Unmute Tab Audio For Desktop Share

media/audio/virtual_audio_sink.cc

Index: media/audio/virtual_audio_sink.cc
diff --git a/media/audio/virtual_audio_sink.cc b/media/audio/virtual_audio_sink.cc
new file mode 100644
index 0000000000000000000000000000000000000000..1cbe00bc788cd6f0c8a8f7f2fd939494408cc6c1
--- /dev/null
+++ b/media/audio/virtual_audio_sink.cc
@@ -0,0 +1,61 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/audio/virtual_audio_sink.h"
+
+#include "base/callback_helpers.h"
+#include "media/audio/virtual_audio_input_stream.h"
+
+namespace media {
+
+// Buffer size limit is chosen large enough that in the normal case, we do not
+// have data loss.
+constexpr int kBufferSizeSecond = 1;
+
+// This is not the system clock accuracy. But considering the cross-process
+// communication, there is fluctuation between the actual and the ideal instant
+// when we receive the audio data. Testing shows the fluctuation is on the order
+// of 1 millisecond.
+constexpr int kClockAccuracyMillisecond = 1;
+
+// See AudioShifter comment for detail about this parameter. We just take the
+// suggestion from there.
+constexpr int kAdjustTimeSecond = 1;
+
+VirtualAudioSink::VirtualAudioSink(AudioParameters param,
+                                   VirtualAudioInputStream* target,
+                                   AfterCloseCallback callback)
+    : params_(param),
+      target_(target),
+      shifter_(base::TimeDelta::FromSeconds(kBufferSizeSecond),
+               base::TimeDelta::FromMilliseconds(kClockAccuracyMillisecond),
+               base::TimeDelta::FromSeconds(kAdjustTimeSecond),
+               param.sample_rate(),
+               param.channels()),
+      after_close_callback_(callback) {
+  target_->AddInputProvider(this, params_);
+}
+
+VirtualAudioSink::~VirtualAudioSink() {}
+
+void VirtualAudioSink::Close() {
+  target_->RemoveInputProvider(this, params_);
+  const AfterCloseCallback& cb = base::ResetAndReturn(&after_close_callback_);
+  if (!cb.is_null())
+    cb.Run(this);
+}
+
+void VirtualAudioSink::OnData(const AudioBus& source,
+                              base::TimeTicks reference_time) {
+  std::unique_ptr<AudioBus> source_copy = AudioBus::Create(params_);
+  source.CopyTo(source_copy.get());
+  shifter_.Push(std::move(source_copy), reference_time);
+}
+
+double VirtualAudioSink::ProvideInput(AudioBus* audio_bus,
+                                      base::TimeDelta buffer_delay) {
+  shifter_.Pull(audio_bus, base::TimeTicks::Now() + buffer_delay);
+  return 1;
+}
+}