Enable audio desktop mirroring.

Define getUserMedia mandatory constraint {chromeMediaSource:"system"}
to indicate audio loopback (post-mix system audio). Add plumbing in
MediaCaptureDevicesDispatcher, AudioManagerCras and CrasInputStream
classes to support the loopback path.

BUG=261383
TEST=manually verify audio mirroring with a modified extension
R=dalecurtis@chromium.org, miu@chromium.org, piman@chromium.org, xians@chromium.org

Review URL: https://codereview.chromium.org/20847002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@215077 0039d316-1c4b-4281-b951-d872f2087c98

5 files changed, 34 insertions, 17 deletions

diff --git a/media/audio/cras/audio_manager_cras.cc b/media/audio/cras/audio_manager_cras.cc
index 73d689a..165d642 100644
--- a/media/audio/cras/audio_manager_cras.cc
+++ b/media/audio/cras/audio_manager_cras.cc
@@ -22,6 +22,8 @@ static const int kMaxOutputStreams = 50;
 // Default sample rate for input and output streams.
 static const int kDefaultSampleRate = 48000;
 
+const char AudioManagerCras::kLoopbackDeviceId[] = "loopback";
+
 bool AudioManagerCras::HasAudioOutputDevices() {
   return true;
 }
@@ -52,7 +54,8 @@ void AudioManagerCras::GetAudioInputDeviceNames(
 AudioParameters AudioManagerCras::GetInputStreamParameters(
     const std::string& device_id) {
   static const int kDefaultInputBufferSize = 1024;
-
+  // TODO(hshi): Fine-tune audio parameters based on |device_id|. The optimal
+  // parameters for the loopback stream may differ from the default.
   return AudioParameters(
       AudioParameters::AUDIO_PCM_LOW_LATENCY, CHANNEL_LAYOUT_STEREO,
       kDefaultSampleRate, 16, kDefaultInputBufferSize);
@@ -124,7 +127,7 @@ AudioOutputStream* AudioManagerCras::MakeOutputStream(
 
 AudioInputStream* AudioManagerCras::MakeInputStream(
     const AudioParameters& params, const std::string& device_id) {
-  return new CrasInputStream(params, this);
+  return new CrasInputStream(params, this, device_id);
 }
 
 }  // namespace media
diff --git a/media/audio/cras/audio_manager_cras.h b/media/audio/cras/audio_manager_cras.h
index 4e69c8f..fdc5b02 100644
--- a/media/audio/cras/audio_manager_cras.h
+++ b/media/audio/cras/audio_manager_cras.h
@@ -15,6 +15,10 @@ namespace media {
 
 class MEDIA_EXPORT AudioManagerCras : public AudioManagerBase {
  public:
+  // Unique ID of the "loopback" input device. This device captures post-mix,
+  // pre-DSP system audio.
+  static const char kLoopbackDeviceId[];
+
   AudioManagerCras();
 
   // AudioManager implementation.
diff --git a/media/audio/cras/cras_input.cc b/media/audio/cras/cras_input.cc
index dec96b8..a82fe28 100644
--- a/media/audio/cras/cras_input.cc
+++ b/media/audio/cras/cras_input.cc
@@ -17,14 +17,18 @@
 namespace media {
 
 CrasInputStream::CrasInputStream(const AudioParameters& params,
-                                 AudioManagerCras* manager)
+                                 AudioManagerCras* manager,
+                                 const std::string& device_id)
     : audio_manager_(manager),
       bytes_per_frame_(0),
       callback_(NULL),
       client_(NULL),
       params_(params),
       started_(false),
-      stream_id_(0) {
+      stream_id_(0),
+      stream_direction_(device_id == AudioManagerCras::kLoopbackDeviceId
+                            ? CRAS_STREAM_POST_MIX_PRE_DSP
+                            : CRAS_STREAM_INPUT) {
   DCHECK(audio_manager_);
 }
 
@@ -127,7 +131,7 @@ void CrasInputStream::Start(AudioInputCallback* callback) {
 
   unsigned int frames_per_packet = params_.frames_per_buffer();
   cras_stream_params* stream_params = cras_client_stream_params_create(
-      CRAS_STREAM_INPUT,
+      stream_direction_,
       frames_per_packet,  // Total latency.
       frames_per_packet,  // Call back when this many ready.
       frames_per_packet,  // Minimum Callback level ignored for capture streams.
diff --git a/media/audio/cras/cras_input.h b/media/audio/cras/cras_input.h
index 1b2a611..dd2cb54 100644
--- a/media/audio/cras/cras_input.h
+++ b/media/audio/cras/cras_input.h
@@ -27,7 +27,8 @@ class CrasInputStream : public AgcAudioStream<AudioInputStream> {
  public:
   // The ctor takes all the usual parameters, plus |manager| which is the
   // audio manager who is creating this object.
-  CrasInputStream(const AudioParameters& params, AudioManagerCras* manager);
+  CrasInputStream(const AudioParameters& params, AudioManagerCras* manager,
+                  const std::string& device_id);
 
   // The dtor is typically called by the AudioManager only and it is usually
   // triggered by calling AudioOutputStream::Close().
@@ -76,7 +77,7 @@ class CrasInputStream : public AgcAudioStream<AudioInputStream> {
   // want circular references.  Additionally, stream objects live on the audio
   // thread, which is owned by the audio manager and we don't want to addref
   // the manager from that thread.
-  AudioManagerCras* audio_manager_;
+  AudioManagerCras* const audio_manager_;
 
   // Size of frame in bytes.
   uint32 bytes_per_frame_;
@@ -88,7 +89,7 @@ class CrasInputStream : public AgcAudioStream<AudioInputStream> {
   cras_client* client_;
 
   // PCM parameters for the stream.
-  AudioParameters params_;
+  const AudioParameters params_;
 
   // True if the stream has been started.
   bool started_;
@@ -96,6 +97,9 @@ class CrasInputStream : public AgcAudioStream<AudioInputStream> {
   // ID of the playing stream.
   cras_stream_id_t stream_id_;
 
+  // Direction of the stream.
+  const CRAS_STREAM_DIRECTION stream_direction_;
+
   DISALLOW_COPY_AND_ASSIGN(CrasInputStream);
 };
 
diff --git a/media/audio/cras/cras_input_unittest.cc b/media/audio/cras/cras_input_unittest.cc
index aba89f3..27ea985 100644
--- a/media/audio/cras/cras_input_unittest.cc
+++ b/media/audio/cras/cras_input_unittest.cc
@@ -62,13 +62,14 @@ class CrasInputStreamTest : public testing::Test {
                            kTestSampleRate,
                            kTestBitsPerSample,
                            samples_per_packet);
-    return new CrasInputStream(params, mock_manager_.get());
+    return new CrasInputStream(params, mock_manager_.get(),
+                               AudioManagerBase::kDefaultDeviceId);
   }
 
   void CaptureSomeFrames(const AudioParameters &params,
                          unsigned int duration_ms) {
-    CrasInputStream* test_stream = new CrasInputStream(params,
-                                                       mock_manager_.get());
+    CrasInputStream* test_stream = new CrasInputStream(
+        params, mock_manager_.get(), AudioManagerBase::kDefaultDeviceId);
 
     ASSERT_TRUE(test_stream->Open());
 
@@ -137,8 +138,8 @@ TEST_F(CrasInputStreamTest, BadBitsPerSample) {
                                  kTestSampleRate,
                                  kTestBitsPerSample - 1,
                                  kTestFramesPerPacket);
-  CrasInputStream* test_stream =
-      new CrasInputStream(bad_bps_params, mock_manager_.get());
+  CrasInputStream* test_stream = new CrasInputStream(
+      bad_bps_params, mock_manager_.get(), AudioManagerBase::kDefaultDeviceId);
   EXPECT_FALSE(test_stream->Open());
   test_stream->Close();
 }
@@ -149,8 +150,9 @@ TEST_F(CrasInputStreamTest, BadFormat) {
                                     kTestSampleRate,
                                     kTestBitsPerSample,
                                     kTestFramesPerPacket);
-  CrasInputStream* test_stream =
-      new CrasInputStream(bad_format_params, mock_manager_.get());
+  CrasInputStream* test_stream = new CrasInputStream(
+      bad_format_params, mock_manager_.get(),
+      AudioManagerBase::kDefaultDeviceId);
   EXPECT_FALSE(test_stream->Open());
   test_stream->Close();
 }
@@ -161,8 +163,8 @@ TEST_F(CrasInputStreamTest, BadSampleRate) {
                                   0,
                                   kTestBitsPerSample,
                                   kTestFramesPerPacket);
-  CrasInputStream* test_stream =
-      new CrasInputStream(bad_rate_params, mock_manager_.get());
+  CrasInputStream* test_stream = new CrasInputStream(
+      bad_rate_params, mock_manager_.get(), AudioManagerBase::kDefaultDeviceId);
   EXPECT_FALSE(test_stream->Open());
   test_stream->Close();
 }