WebContentsAudioMuter: Mute all audio output from a WebContentsImpl.

content/browser/media/capture/web_contents_audio_muter.cc

+// Copyright 2014 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 "content/browser/media/capture/web_contents_audio_muter.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "content/browser/media/capture/audio_mirroring_manager.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/render_frame_host.h"
+#include "content/public/browser/web_contents.h"
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_manager.h"
+#include "media/audio/fake_audio_consumer.h"
+#include "media/base/bind_to_current_loop.h"
+
+namespace content {
+
+namespace {
+
+// An AudioOutputStream that pumps audio data, but does nothing with it.
+// Pumping the audio data is necessary because video playback is synchronized to
+// the audio stream and will freeze otherwise.
+//
+// TODO(miu): media::FakeAudioOutputStream does pretty much the same thing as
+// this class, but requires construction/destruction via media::AudioManagerBase
+// on the audio thread.  Once that's fixed, this class will no longer be needed.
+// http://crbug.com/416278
+class AudioDiscarder : public media::AudioOutputStream {
+ public:
+  explicit AudioDiscarder(const media::AudioParameters& params)
+      : consumer_(media::AudioManager::Get()->GetWorkerTaskRunner(), params) {}
+
+  // AudioOutputStream implementation.
+  virtual bool Open() OVERRIDE { return true; }
+  virtual void Start(AudioSourceCallback* callback) OVERRIDE {
+    consumer_.Start(base::Bind(&AudioDiscarder::FetchAudioData, callback));
+  }
+  virtual void Stop() OVERRIDE { consumer_.Stop(); }
+  virtual void SetVolume(double volume) OVERRIDE {}
+  virtual void GetVolume(double* volume) OVERRIDE { *volume = 0; }
+  virtual void Close() OVERRIDE { delete this; }
+
+ private:
+  virtual ~AudioDiscarder() {}
+
+  static void FetchAudioData(AudioSourceCallback* callback,
+                             media::AudioBus* audio_bus) {
+    callback->OnMoreData(audio_bus, media::AudioBuffersState());
+  }
+
+  // Calls FetchAudioData() at regular intervals and discards the data.
+  media::FakeAudioConsumer consumer_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioDiscarder);
+};
+
+}  // namespace
+
+// A simple AudioMirroringManager::MirroringDestination implementation that
+// identifies the audio streams rendered by a WebContents and provides
+// AudioDiscarders to AudioMirroringManager.
+class WebContentsAudioMuter::MuteDestination
+    : public base::RefCountedThreadSafe<MuteDestination>,

[DaleCurtis, 2014/09/22 17:45:45]

I think it's easier to reason about if you just use a WeakPtrFactory. 

[miu, 2014/09/22 19:44:58]

There are tasks posted to two different threads that need to dereference the
pointer to WebContentsAudioMuter, so a WeakPtr won't be sufficient.

+      public AudioMirroringManager::MirroringDestination {
+ public:
+  explicit MuteDestination(WebContents* web_contents)
+      : web_contents_(web_contents) {}
+
+ private:
+  friend class base::RefCountedThreadSafe<MuteDestination>;
+
+  typedef AudioMirroringManager::SourceFrameRef SourceFrameRef;
+
+  virtual ~MuteDestination() {}
+
+  virtual void QueryForMatches(
+      const std::set<SourceFrameRef>& candidates,
+      const MatchesCallback& results_callback) OVERRIDE {
+    BrowserThread::PostTask(
+        BrowserThread::UI,
+        FROM_HERE,
+        base::Bind(&MuteDestination::QueryForMatchesOnUIThread,
+                   this,
+                   candidates,
+                   media::BindToCurrentLoop(results_callback)));
+  }
+
+  void QueryForMatchesOnUIThread(const std::set<SourceFrameRef>& candidates,
+                                 const MatchesCallback& results_callback) {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
+    std::set<SourceFrameRef> matches;
+    // Add each ID to |matches| if it maps to a RenderFrameHost that maps to the
+    // WebContents being muted.
+    for (std::set<SourceFrameRef>::const_iterator i = candidates.begin();
+         i != candidates.end(); ++i) {
+      WebContents* const contents_containing_frame =
+          WebContents::FromRenderFrameHost(
+              RenderFrameHost::FromID(i->first, i->second));
+      if (contents_containing_frame == web_contents_)
+        matches.insert(*i);
+    }
+    results_callback.Run(matches);
+  }
+
+  virtual media::AudioOutputStream* AddInput(
+      const media::AudioParameters& params) OVERRIDE {
+    return new AudioDiscarder(params);
+  }
+
+  WebContents* const web_contents_;
+
+  DISALLOW_COPY_AND_ASSIGN(MuteDestination);
+};
+
+

[DaleCurtis, 2014/09/22 17:45:45]

Extra line.

[miu, 2014/09/22 19:44:58]

Done.

+WebContentsAudioMuter::WebContentsAudioMuter(WebContents* web_contents)
+    : destination_(new MuteDestination(web_contents)), is_muting_(false) {

[DaleCurtis, 2014/09/22 17:45:45]

Stack allocate?

[miu, 2014/09/22 19:44:58]

Not sure what you mean.  If you're suggesting I make MuteDestination a member
via composition (rather than pointer-to-MuteDestination), I can't do that since
I would need to keep the WebContentsAudioMuter alive until the
Start/StopMirroring() tasks on the IO thread complete.  This would mean blocking
the UI thread on calls to the Start/StopMuting() methods.

+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+}
+
+WebContentsAudioMuter::~WebContentsAudioMuter() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  StopMuting();
+}
+
+void WebContentsAudioMuter::StartMuting() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (is_muting_)
+    return;
+  is_muting_ = true;
+  BrowserThread::PostTask(
+      BrowserThread::IO,
+      FROM_HERE,
+      base::Bind(&AudioMirroringManager::StartMirroring,
+                 base::Unretained(AudioMirroringManager::GetInstance()),
+                 destination_));
+}
+
+void WebContentsAudioMuter::StopMuting() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (!is_muting_)
+    return;
+  is_muting_ = false;
+  BrowserThread::PostTask(
+      BrowserThread::IO,
+      FROM_HERE,
+      base::Bind(&AudioMirroringManager::StopMirroring,
+                 base::Unretained(AudioMirroringManager::GetInstance()),
+                 destination_));
+}
+
+}  // namespace content