[Chromecast] Enable "what's playing" for external audio pipeline.

. Add ExternalMediaMetadata to the external input source and state.
. Add ExternalMediaMetadataChangeObserver for the external pipeline to report media state change.
. Report external pipeline state to the Assistant Server via MediaParams.

Design doc: internal http://go/voice-control-for-external-audio-pipeline

Bug: internal b/80156336
Change-Id: I68ec11cc6fe4f368c34fe705c05a0f50ee9011cc
Reviewed-on: https://chromium-review.googlesource.com/1192116Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Kenneth MacKay <kmackay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588177}

chromecast/media/audio/external_audio_pipeline_dummy.cc

@@ -52,6 +52,16 @@ void ExternalAudioPipelineShlib::RemoveExternalLoopbackAudioObserver(
   NOTREACHED();
 }
 
+void ExternalAudioPipelineShlib::AddExternalMediaMetadataChangeObserver(
+    ExternalMediaMetadataChangeObserver* observer) {
+  NOTREACHED();
+}
+
+void ExternalAudioPipelineShlib::RemoveExternalMediaMetadataChangeObserver(
+    ExternalMediaMetadataChangeObserver* observer) {
+  NOTREACHED();
+}
+
 std::unique_ptr<MixerOutputStream>
 ExternalAudioPipelineShlib::CreateMixerOutputStream() {
   NOTREACHED();

chromecast/media/audio/external_audio_pipeline_sample.cc

@@ -12,6 +12,9 @@
 #include "chromecast/public/media/external_audio_pipeline_shlib.h"
 #include "chromecast/public/media/mixer_output_stream.h"
 
+using ExternalMediaMetadataChangeObserver = chromecast::media::
+    ExternalAudioPipelineShlib::ExternalMediaMetadataChangeObserver;
+
 namespace chromecast {
 namespace media {
 
@@ -110,6 +113,12 @@ void ExternalAudioPipelineShlib::RemoveExternalLoopbackAudioObserver(
   g_test_loop_back.RemoveObserver(observer);
 }
 
+void ExternalAudioPipelineShlib::AddExternalMediaMetadataChangeObserver(
+    ExternalMediaMetadataChangeObserver* observer) {}
+
+void ExternalAudioPipelineShlib::RemoveExternalMediaMetadataChangeObserver(
+    ExternalMediaMetadataChangeObserver* observer) {}
+
 std::unique_ptr<MixerOutputStream>
 ExternalAudioPipelineShlib::CreateMixerOutputStream() {
   return std::make_unique<MixerOutputStreamTest>(&g_test_loop_back);

chromecast/public/media/external_audio_pipeline_shlib.h

@@ -17,6 +17,21 @@ namespace media {
 
 class CHROMECAST_EXPORT ExternalAudioPipelineShlib {
  public:
+  // Represents a media input source of the external media pipeline.
+  enum class MediaInputSource {
+    UNKNOWN_INPUT_SOURCE,
+    HDMI,
+    AIRPLAY,
+  };
+
+  // Represents a media playback state of the external media pipeline.
+  enum class MediaPlaybackState {
+    UNKNOWN_STATE,
+    STOPPED,
+    PAUSED,
+    PLAYING,
+  };
+
   // Observer for reporting requests for media volume change/muting from the
   // external media pipeline. The external pipeline should communicate the media
   // volume change requests through this observer and otherwise shouldn't change
@@ -40,6 +55,33 @@ class CHROMECAST_EXPORT ExternalAudioPipelineShlib {
     virtual ~ExternalMediaVolumeChangeRequestObserver() = default;
   };
 
+  // Media metadata which can be acquired from the external pipeline.
+  struct ExternalMediaMetadata {
+    ExternalMediaMetadata();
+    ExternalMediaMetadata(const ExternalMediaMetadata& other);
+    ~ExternalMediaMetadata();
+
+    std::string title;
+    std::string artist;
+    std::string album;
+    std::string genre;
+    int track_num = -1;
+    MediaInputSource source = MediaInputSource::HDMI;
+    MediaPlaybackState state = MediaPlaybackState::UNKNOWN_STATE;
+  };
+
+  // Observer for reporting media metadata change from the external media
+  // pipeline, e.g., title, artist, input source, play back state, and etc.
+  class ExternalMediaMetadataChangeObserver {
+   public:
+    // Called when media metadata is updated.
+    virtual void OnExternalMediaMetadataChanged(
+        const ExternalMediaMetadata& metadata) = 0;
+
+   protected:
+    virtual ~ExternalMediaMetadataChangeObserver() = default;
+  };
+
   // Returns whether this shlib is supported. If this returns true, it indicates
   // that the platform uses an external audio pipeline that needs to be combined
   // with Cast's media pipeline.
@@ -84,11 +126,29 @@ class CHROMECAST_EXPORT ExternalAudioPipelineShlib {
   static void RemoveExternalLoopbackAudioObserver(
       CastMediaShlib::LoopbackAudioObserver* observer);
 
+  // Adds an external media metadata observer.
+  static void AddExternalMediaMetadataChangeObserver(
+      ExternalMediaMetadataChangeObserver* observer) __attribute__((__weak__));
+
+  // Removes an external media volume observer. After this is called, the
+  // implementation must not call any more methods on the observer.
+  static void RemoveExternalMediaMetadataChangeObserver(
+      ExternalMediaMetadataChangeObserver* observer) __attribute__((__weak__));
+
   // Returns an instance of MixerOutputStream from the shared library.
   // Caller will take ownership of the returned pointer.
   static std::unique_ptr<MixerOutputStream> CreateMixerOutputStream();
 };
 
+inline ExternalAudioPipelineShlib::ExternalMediaMetadata::
+    ExternalMediaMetadata() = default;
+
+inline ExternalAudioPipelineShlib::ExternalMediaMetadata::ExternalMediaMetadata(
+    const ExternalMediaMetadata& other) = default;
+
+inline ExternalAudioPipelineShlib::ExternalMediaMetadata::
+    ~ExternalMediaMetadata() = default;
+
 }  // namespace media
 }  // namespace chromecast