Unmute Tab Audio For Desktop Share

media/audio/virtual_audio_sink.cc

+// Copyright (c) 2016 The Chromium Authors. All rights reserved.

[miu, 2016/05/02 20:06:14]

No "(c)" in copyright headers anymore.

[qiangchen, 2016/05/03 16:58:23]

Done.

+// 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 {
+
+static const base::TimeDelta kBufferSize = base::TimeDelta::FromSeconds(1);

[miu, 2016/05/02 20:06:14]

1. How were these values chosen?  Please document the decisions you made here.

2. We can't use base::TimeDelta in global static constants (yet--it's coming
soon). For now, you'll need to define these like so:

  constexpr int kBufferSizeSeconds = 1;
  constexpr int kClockAccuracyMilliseconds = 1;
  ...

[qiangchen, 2016/05/03 16:58:23]

Done.

+static const base::TimeDelta kClockAccuracy =
+    base::TimeDelta::FromMilliseconds(1);
+static const base::TimeDelta kAdjustTime = base::TimeDelta::FromSeconds(1);
+
+VirtualAudioSink::VirtualAudioSink(AudioParameters param,
+                                   VirtualAudioInputStream* target,
+                                   AfterCloseCallback callback)
+    : params_(param),
+      target_(target),
+      shifter_(kBufferSize,
+               kClockAccuracy,
+               kAdjustTime,
+               param.sample_rate(),
+               param.channels()),
+      after_close_callback_(callback) {
+  target_->AddInputProvider(this, params_);
+}
+
+VirtualAudioSink::~VirtualAudioSink() {}
+
+void VirtualAudioSink::Close() {
+  target_->RemoveInputProvider(this, params_);
+  AfterCloseCallback cb = base::ResetAndReturn(&after_close_callback_);

[miu, 2016/05/02 20:06:13]

You're making another copy of the callback here. Please do either:

  if (!after_close_callback_.is_null())
    base::ResetAndReturn(&after_close_callback_).Run(this);

-or-

  const AfterCloseCallback& cb = base::ResetAndReturn(...);
  if (!cb.is_null())
    cb.Run(this);

(IMHO, the first form is simpler.)

[qiangchen, 2016/05/03 16:58:23]

Done.

+  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;
+}
+}