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;
+
+// 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;

[miu, 2016/05/28 02:45:00]

This seems wrong, given the code comments here:

https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/m...

[qiangchen, 2016/05/31 21:17:33]

Done.

+
+// 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()),
+      task_runner_(target->GetTaskRunner()),
+      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) {
+  // We must copy data here, and should not pass |source| to the

[miu, 2016/05/28 02:45:00]

Given this should be done in AudioOutputController (one copy made there). Please
revert virtual_audio_sink.h/.cc back to the way they were in Patch Set 5.

[qiangchen, 2016/05/31 21:17:33]

Then I think we need a lock for shifter_, otherwise it is possible that Pull and
Push are called simultaneously.

[miu, 2016/06/01 00:29:42]

Yep. Sounds good to me.

[qiangchen, 2016/06/01 17:51:11]

Acknowledged.

+  // |task_runner_|, because there is no guarantee that |source| is still a
+  // valid object when the posted task is run.
+  std::unique_ptr<AudioBus> source_copy(AudioBus::Create(params_));
+  source.CopyTo(source_copy.get());
+  task_runner_->PostTask(FROM_HERE,
+                         base::Bind(&VirtualAudioSink::StoreData, AsWeakPtr(),
+                                    source_copy.release(), reference_time));
+}
+
+void VirtualAudioSink::StoreData(AudioBus* source,
+                                 base::TimeTicks reference_time) {
+  shifter_.Push(std::unique_ptr<AudioBus>(source), reference_time);
+}
+
+double VirtualAudioSink::ProvideInput(AudioBus* audio_bus,
+                                      base::TimeDelta buffer_delay) {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+  shifter_.Pull(audio_bus, base::TimeTicks::Now() + buffer_delay);
+  return 1;
+}
+}