diff --git a/services/audioflinger/PlaybackTracks.h b/services/audioflinger/PlaybackTracks.h
index ea01a25..a78be99 100644
--- a/services/audioflinger/PlaybackTracks.h
+++ b/services/audioflinger/PlaybackTracks.h
@@ -93,6 +93,23 @@
                                 const sp<media::VolumeShaper::Operation>& operation);
     sp<media::VolumeShaper::State> getVolumeShaperState(int id);
     sp<media::VolumeHandler>   getVolumeHandler() { return mVolumeHandler; }
+    /** Set the computed normalized final volume of the track.
+     * !masterMute * masterVolume * streamVolume * averageLRVolume */
+    void                setFinalVolume(float volume);
+    float               getFinalVolume() const { return mFinalVolume; }
+
+    /** @return true if the track has changed (metadata or volume) since
+     *          the last time this function was called,
+     *          true if this function was never called since the track creation,
+     *          false otherwise.
+     *  Thread safe.
+     */
+    bool            readAndClearHasChanged() { return !mChangeNotified.test_and_set(); }
+
+    using SourceMetadatas = std::vector<playback_track_metadata_t>;
+    using MetadataInserter = std::back_insert_iterator<SourceMetadatas>;
+    /** Copy the track metadata in the provided iterator. Thread safe. */
+    virtual void    copyMetadataTo(MetadataInserter& backInserter) const;
 
 protected:
     // for numerous
@@ -133,6 +150,8 @@
     bool presentationComplete(int64_t framesWritten, size_t audioHalFrames);
     void signalClientFlag(int32_t flag);
 
+    /** Set that a metadata has changed and needs to be notified to backend. Thread safe. */
+    void setMetadataHasChanged() { mChangeNotified.clear(); }
 public:
     void triggerEvents(AudioSystem::sync_event_t type);
     virtual void invalidate();
@@ -182,10 +201,13 @@
     volatile float      mCachedVolume;  // combined master volume and stream type volume;
                                         // 'volatile' means accessed without lock or
                                         // barrier, but is read/written atomically
+    float               mFinalVolume; // combine master volume, stream type volume and track volume
     sp<AudioTrackServerProxy>  mAudioTrackServerProxy;
     bool                mResumeToStopping; // track was paused in stopping state.
     bool                mFlushHwPending; // track requests for thread flush
     audio_output_flags_t mFlags;
+    // If the last track change was notified to the client with readAndClearHasChanged
+    std::atomic_flag     mChangeNotified = ATOMIC_FLAG_INIT;
 };  // end of Track
 
 
@@ -216,8 +238,11 @@
             bool        isActive() const { return mActive; }
     const wp<ThreadBase>& thread() const { return mThread; }
 
-private:
+            void        copyMetadataTo(MetadataInserter& backInserter) const override;
+    /** Set the metadatas of the upstream tracks. Thread safe. */
+            void        setMetadatas(const SourceMetadatas& metadatas);
 
+private:
     status_t            obtainBuffer(AudioBufferProvider::Buffer* buffer,
                                      uint32_t waitTimeMs);
     void                clearBufferQueue();
@@ -232,6 +257,20 @@
     bool                        mActive;
     DuplicatingThread* const    mSourceThread; // for waitTimeMs() in write()
     sp<AudioTrackClientProxy>   mClientProxy;
+    /** Attributes of the source tracks.
+     *
+     * This member must be accessed with mTrackMetadatasMutex taken.
+     * There is one writer (duplicating thread) and one reader (downstream mixer).
+     *
+     * That means that the duplicating thread can block the downstream mixer
+     * thread and vice versa for the time of the copy.
+     * If this becomes an issue, the metadata could be stored in an atomic raw pointer,
+     * and a exchange with nullptr and delete can be used.
+     * Alternatively a read-copy-update might be implemented.
+     */
+    SourceMetadatas mTrackMetadatas;
+    /** Protects mTrackMetadatas against concurrent access. */
+    mutable std::mutex mTrackMetadatasMutex;
 };  // end of OutputTrack
 
 // playback track, used by PatchPanel