Unmute Tab Audio For Desktop Share

media/audio/virtual_audio_sink.cc

+// 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/bind.h"
+#include "base/callback_helpers.h"
+#include "base/location.h"
+#include "base/single_thread_task_runner.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;
+
+// The accuracy contains two components: 1. the cross-process communication,
+// there is fluctuation between the actual and the ideal instant when we receive
+// the audio data; 2. The system clock resolution: worst case is ~15ms on
+// Windows machines without a working high-resolution clock.
+constexpr int kClockAccuracyMillisecond = 20;
+
+// See AudioShifter comment for detail about this parameter. We just take the
+// suggestion from there.
+constexpr int kAdjustTimeSecond = 1;
+
+VirtualAudioSink::VirtualAudioSink(const AudioParameters& param,
+                                   VirtualAudioInputStream* target,
+                                   const 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(std::unique_ptr<AudioBus> source,
+                              base::TimeTicks reference_time) {
+  base::AutoLock lock(shifter_lock_);
+  shifter_.Push(std::move(source), reference_time);
+}
+
+double VirtualAudioSink::ProvideInput(AudioBus* audio_bus,
+                                      uint32_t frames_delayed) {
+  base::AutoLock lock(shifter_lock_);
+  shifter_.Pull(audio_bus,
+                base::TimeTicks::Now() +
+                    base::TimeDelta::FromMicroseconds(
+                        frames_delayed * params_.GetMicrosecondsPerFrame()));
+  return 1;
+}
+}