diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index 0e2da4e..3302868 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -19,8 +19,11 @@
 #define ANDROID_AUDIO_FLINGER_H
 
 #include "Configuration.h"
+#include <atomic>
+#include <mutex>
 #include <deque>
 #include <map>
+#include <vector>
 #include <stdint.h>
 #include <sys/types.h>
 #include <limits.h>
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
diff --git a/services/audioflinger/Threads.cpp b/services/audioflinger/Threads.cpp
index 160aa45..43a8b50 100644
--- a/services/audioflinger/Threads.cpp
+++ b/services/audioflinger/Threads.cpp
@@ -2623,27 +2623,33 @@
 
 void AudioFlinger::PlaybackThread::updateMetadata_l()
 {
-    // TODO: add volume support
-    if (mOutput == nullptr || mOutput->stream == nullptr ||
-            !mActiveTracks.readAndClearHasChanged()) {
-        return;
+    if (mOutput == nullptr || mOutput->stream == nullptr ) {
+        return; // That should not happen
+    }
+    bool hasChanged = mActiveTracks.readAndClearHasChanged();
+    for (const sp<Track> &track : mActiveTracks) {
+        // Do not short-circuit as all hasChanged states must be reset
+        // as all the metadata are going to be sent
+        hasChanged |= track->readAndClearHasChanged();
+    }
+    if (!hasChanged) {
+        return; // nothing to do
     }
     StreamOutHalInterface::SourceMetadata metadata;
+    auto backInserter = std::back_inserter(metadata.tracks);
     for (const sp<Track> &track : mActiveTracks) {
         // No track is invalid as this is called after prepareTrack_l in the same critical section
-        if (track->isOutputTrack()) {
-            // TODO: OutputTrack (used for duplication) are currently not supported
-            continue;
-        }
-        metadata.tracks.push_back({
-                .usage = track->attributes().usage,
-                .content_type = track->attributes().content_type,
-                .gain = 1,
-        });
+        track->copyMetadataTo(backInserter);
     }
-    mOutput->stream->updateSourceMetadata(metadata);
+    sendMetadataToBackend_l(metadata);
 }
 
+void AudioFlinger::PlaybackThread::sendMetadataToBackend_l(
+        const StreamOutHalInterface::SourceMetadata& metadata)
+{
+    mOutput->stream->updateSourceMetadata(metadata);
+};
+
 status_t AudioFlinger::PlaybackThread::getRenderPosition(uint32_t *halFrames, uint32_t *dspFrames)
 {
     if (halFrames == NULL || dspFrames == NULL) {
@@ -4381,13 +4387,19 @@
                     didModify = true;
                     // no acknowledgement required for newly active tracks
                 }
+                sp<AudioTrackServerProxy> proxy = track->mAudioTrackServerProxy;
                 // cache the combined master volume and stream type volume for fast mixer; this
                 // lacks any synchronization or barrier so VolumeProvider may read a stale value
                 const float vh = track->getVolumeHandler()->getVolume(
-                        track->mAudioTrackServerProxy->framesReleased()).first;
-                track->mCachedVolume = masterVolume
+                        proxy->framesReleased()).first;
+                float volume = masterVolume
                         * mStreamTypes[track->streamType()].volume
                         * vh;
+                track->mCachedVolume = masterVolume;
+                gain_minifloat_packed_t vlr = proxy->getVolumeLR();
+                float vlf = volume * float_from_gain(gain_minifloat_unpack_left(vlr));
+                float vrf = volume * float_from_gain(gain_minifloat_unpack_right(vlr));
+                track->setFinalVolume((vlf + vrf) / 2.f);
                 ++fastTracks;
             } else {
                 // was it previously active?
@@ -4564,6 +4576,8 @@
                 vaf = v * sendLevel * (1. / MAX_GAIN_INT);
             }
 
+            track->setFinalVolume((vrf + vlf) / 2.f);
+
             // Delegate volume control to effect in track effect chain if needed
             if (chain != 0 && chain->setVolume_l(&vl, &vr)) {
                 // Do not ramp volume if volume is controlled by effect
@@ -5096,6 +5110,7 @@
     }
 
     if (lastTrack) {
+        track->setFinalVolume((left + right) / 2.f);
         if (left != mLeftVolFloat || right != mRightVolFloat) {
             mLeftVolFloat = left;
             mRightVolFloat = right;
@@ -6153,14 +6168,12 @@
     return true;
 }
 
-void AudioFlinger::DuplicatingThread::updateMetadata_l()
+void AudioFlinger::DuplicatingThread::sendMetadataToBackend_l(
+        const StreamOutHalInterface::SourceMetadata& metadata)
 {
-    // TODO: The duplicated track metadata needs to be pushed to downstream
-    // but this information can be read at any time by the downstream threads.
-    // Taking the lock of any downstream threads is no possible due to cross deadlock risks
-    // (eg: during effect move).
-    // A lock-free structure needs to be used to shared the metadata, probably an atomic
-    // pointer to a metadata vector in each output tracks.
+    for (auto& outputTrack : outputTracks) { // not mOutputTracks
+        outputTrack->setMetadatas(metadata.tracks);
+    }
 }
 
 uint32_t AudioFlinger::DuplicatingThread::activeSleepTimeUs() const
diff --git a/services/audioflinger/Threads.h b/services/audioflinger/Threads.h
index bb81224..5a5961a 100644
--- a/services/audioflinger/Threads.h
+++ b/services/audioflinger/Threads.h
@@ -566,8 +566,8 @@
                     // periodically called in the threadLoop() to update power state uids.
                     void            updatePowerState(sp<ThreadBase> thread, bool force = false);
 
-                    /** @return true if the active tracks have changed since the last time
-                     *          this function was called or the vector was created. */
+                    /** @return true if one or move active tracks was added or removed since the
+                     *          last time this function was called or the vector was created. */
                     bool            readAndClearHasChanged();
 
                 private:
@@ -588,7 +588,7 @@
                     int                 mLastActiveTracksGeneration;
                     wp<T>               mLatestActiveTrack; // latest track added to ActiveTracks
                     SimpleLog * const   mLocalLog;
-                    // If the active tracks have changed since last call to readAndClearHasChanged
+                    // If the vector has changed since last call to readAndClearHasChanged
                     bool                mHasChanged = false;
                 };
 
@@ -927,7 +927,8 @@
     void        removeTrack_l(const sp<Track>& track);
 
     void        readOutputParameters_l();
-    void        updateMetadata_l() override;
+    void        updateMetadata_l() final;
+    virtual void sendMetadataToBackend_l(const StreamOutHalInterface::SourceMetadata& metadata);
 
     virtual void dumpInternals(int fd, const Vector<String16>& args);
     void        dumpTracks(int fd, const Vector<String16>& args);
@@ -1287,7 +1288,8 @@
                 void        removeOutputTrack(MixerThread* thread);
                 uint32_t    waitTimeMs() const { return mWaitTimeMs; }
 
-                void        updateMetadata_l() override;
+                void        sendMetadataToBackend_l(
+                        const StreamOutHalInterface::SourceMetadata& metadata) override;
 protected:
     virtual     uint32_t    activeSleepTimeUs() const;
 
diff --git a/services/audioflinger/Tracks.cpp b/services/audioflinger/Tracks.cpp
index 236412b..ee9ce84 100644
--- a/services/audioflinger/Tracks.cpp
+++ b/services/audioflinger/Tracks.cpp
@@ -407,6 +407,9 @@
     // mSinkTimestamp
     mFastIndex(-1),
     mCachedVolume(1.0),
+    /* The track might not play immediately after being active, similarly as if its volume was 0.
+     * When the track starts playing, its volume will be computed. */
+    mFinalVolume(0.f),
     mResumeToStopping(false),
     mFlushHwPending(false),
     mFlags(flags)
@@ -997,6 +1000,23 @@
     return mVolumeHandler->getVolumeShaperState(id);
 }
 
+void AudioFlinger::PlaybackThread::Track::setFinalVolume(float volume)
+{
+    if (mFinalVolume != volume) { // Compare to an epsilon if too many meaningless updates
+        mFinalVolume = volume;
+        setMetadataHasChanged();
+    }
+}
+
+void AudioFlinger::PlaybackThread::Track::copyMetadataTo(MetadataInserter& backInserter) const
+{
+    *backInserter++ = {
+            .usage = mAttr.usage,
+            .content_type = mAttr.content_type,
+            .gain = mFinalVolume,
+    };
+}
+
 status_t AudioFlinger::PlaybackThread::Track::getTimestamp(AudioTimestamp& timestamp)
 {
     if (!isOffloaded() && !isDirect()) {
@@ -1427,6 +1447,21 @@
     return outputBufferFull;
 }
 
+void AudioFlinger::PlaybackThread::OutputTrack::copyMetadataTo(MetadataInserter& backInserter) const
+{
+    std::lock_guard<std::mutex> lock(mTrackMetadatasMutex);
+    backInserter = std::copy(mTrackMetadatas.begin(), mTrackMetadatas.end(), backInserter);
+}
+
+void AudioFlinger::PlaybackThread::OutputTrack::setMetadatas(const SourceMetadatas& metadatas) {
+    {
+        std::lock_guard<std::mutex> lock(mTrackMetadatasMutex);
+        mTrackMetadatas = metadatas;
+    }
+    // No need to adjust metadata track volumes as OutputTrack volumes are always 0dBFS.
+    setMetadataHasChanged();
+}
+
 status_t AudioFlinger::PlaybackThread::OutputTrack::obtainBuffer(
         AudioBufferProvider::Buffer* buffer, uint32_t waitTimeMs)
 {