diff --git a/audio/6.0/Android.bp b/audio/6.0/Android.bp
index dc6bb98..16abc52 100644
--- a/audio/6.0/Android.bp
+++ b/audio/6.0/Android.bp
@@ -15,6 +15,7 @@
         "IStreamIn.hal",
         "IStreamOut.hal",
         "IStreamOutCallback.hal",
+        "IStreamOutEventCallback.hal",
     ],
     interfaces: [
         "android.hardware.audio.common@6.0",
diff --git a/audio/6.0/IStreamOut.hal b/audio/6.0/IStreamOut.hal
index 13a86ec..9da48fe 100644
--- a/audio/6.0/IStreamOut.hal
+++ b/audio/6.0/IStreamOut.hal
@@ -19,6 +19,7 @@
 import android.hardware.audio.common@6.0;
 import IStream;
 import IStreamOutCallback;
+import IStreamOutEventCallback;
 
 interface IStreamOut extends IStream {
     /**
@@ -168,6 +169,18 @@
     clearCallback() generates (Result retval);
 
     /**
+     * Set the callback interface for notifying about an output stream event.
+     *
+     * Calling this method with a null pointer will result in releasing
+     * the local callback proxy on the server side and thus dereference
+     * the callback implementation on the client side.
+     *
+     * @return retval operation completion status.
+     */
+    setEventCallback(IStreamOutEventCallback callback)
+            generates (Result retval);
+
+    /**
      * Returns whether HAL supports pausing and resuming of streams.
      *
      * @return supportsPause true if pausing is supported.
diff --git a/audio/6.0/IStreamOutEventCallback.hal b/audio/6.0/IStreamOutEventCallback.hal
new file mode 100644
index 0000000..de17d73
--- /dev/null
+++ b/audio/6.0/IStreamOutEventCallback.hal
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.hardware.audio@6.0;
+
+/**
+ * Asynchronous stream out event callback interface. The interface provides
+ * a way for the HAL to notify platform when there are changes, e.g. codec
+ * format change, from the lower layer.
+ */
+interface IStreamOutEventCallback {
+    /**
+     * Codec format changed.
+     *
+     * @param audioMetadata is a buffer containing decoded format changes
+     *     reported by codec. The buffer contains data that can be transformed
+     *     to audio metadata, which is a C++ object based map. See
+     *     `system/media/audio_utils/include/audio_utils/Metadata.h` for
+     *     more details.
+     */
+    oneway onCodecFormatChanged(vec<uint8_t> audioMetadata);
+};
diff --git a/audio/core/all-versions/default/StreamOut.cpp b/audio/core/all-versions/default/StreamOut.cpp
index 7a4d72b..150d641 100644
--- a/audio/core/all-versions/default/StreamOut.cpp
+++ b/audio/core/all-versions/default/StreamOut.cpp
@@ -22,6 +22,8 @@
 //#define LOG_NDEBUG 0
 #define ATRACE_TAG ATRACE_TAG_AUDIO
 
+#include <string.h>
+
 #include <memory>
 
 #include <android/log.h>
@@ -612,6 +614,33 @@
     return Result::NOT_SUPPORTED;
 }
 
+Return<Result> StreamOut::setEventCallback(const sp<IStreamOutEventCallback>& callback) {
+    if (mStream->set_event_callback == nullptr) return Result::NOT_SUPPORTED;
+    int result = mStream->set_event_callback(mStream, StreamOut::asyncEventCallback, this);
+    if (result == 0) {
+        mEventCallback = callback;
+    }
+    return Stream::analyzeStatus("set_stream_out_callback", result, {ENOSYS} /*ignore*/);
+}
+
+// static
+int StreamOut::asyncEventCallback(stream_event_callback_type_t event, void* param, void* cookie) {
+    StreamOut* self = reinterpret_cast<StreamOut*>(cookie);
+    sp<IStreamOutEventCallback> eventCallback = self->mEventCallback;
+    if (eventCallback.get() == nullptr) return 0;
+    ALOGV("%s event %d", __func__, event);
+    switch (event) {
+        case STREAM_EVENT_CBK_TYPE_CODEC_FORMAT_CHANGED: {
+            hidl_vec<uint8_t> audioMetadata;
+            audioMetadata.setToExternal((uint8_t*)param, strlen((char*)param));
+            eventCallback->onCodecFormatChanged(audioMetadata);
+        } break;
+        default:
+            ALOGW("%s unknown event %d", __func__, event);
+            break;
+    }
+    return 0;
+}
 #endif
 
 }  // namespace implementation
diff --git a/audio/core/all-versions/default/include/core/default/StreamOut.h b/audio/core/all-versions/default/include/core/default/StreamOut.h
index 5db8626..e647da9 100644
--- a/audio/core/all-versions/default/include/core/default/StreamOut.h
+++ b/audio/core/all-versions/default/include/core/default/StreamOut.h
@@ -133,12 +133,19 @@
     static Result getPresentationPositionImpl(audio_stream_out_t* stream, uint64_t* frames,
                                               TimeSpec* timeStamp);
 
-   private:
+#if MAJOR_VERSION >= 6
+    Return<Result> setEventCallback(const sp<IStreamOutEventCallback>& callback) override;
+#endif
+
+  private:
     const sp<Device> mDevice;
     audio_stream_out_t* mStream;
     const sp<Stream> mStreamCommon;
     const sp<StreamMmap<audio_stream_out_t>> mStreamMmap;
-    sp<IStreamOutCallback> mCallback;
+    sp<IStreamOutCallback> mCallback;  // Callback for non-blocking write and drain
+#if MAJOR_VERSION >= 6
+    sp<IStreamOutEventCallback> mEventCallback;
+#endif
     std::unique_ptr<CommandMQ> mCommandMQ;
     std::unique_ptr<DataMQ> mDataMQ;
     std::unique_ptr<StatusMQ> mStatusMQ;
@@ -149,6 +156,10 @@
     virtual ~StreamOut();
 
     static int asyncCallback(stream_callback_event_t event, void* param, void* cookie);
+
+#if MAJOR_VERSION >= 6
+    static int asyncEventCallback(stream_event_callback_type_t event, void* param, void* cookie);
+#endif
 };
 
 }  // namespace implementation
diff --git a/audio/core/all-versions/vts/functional/6.0/AudioPrimaryHidlHalTest.cpp b/audio/core/all-versions/vts/functional/6.0/AudioPrimaryHidlHalTest.cpp
index 9e2a050..b40a329 100644
--- a/audio/core/all-versions/vts/functional/6.0/AudioPrimaryHidlHalTest.cpp
+++ b/audio/core/all-versions/vts/functional/6.0/AudioPrimaryHidlHalTest.cpp
@@ -251,3 +251,21 @@
 INSTANTIATE_TEST_CASE_P(PlaybackRateParametersHidl, PlaybackRateParametersHidlTest,
                         ::testing::ValuesIn(getOutputDeviceConfigParameters()),
                         &DeviceConfigParameterToString);
+
+/** Stub implementation of IStreamOutEventCallback **/
+class MockOutEventCallbacks : public IStreamOutEventCallback {
+    Return<void> onCodecFormatChanged(const hidl_vec<uint8_t>& audioMetadata __unused) override {
+        return {};
+    }
+};
+
+TEST_P(OutputStreamTest, SetEventCallback) {
+    doc::test("If supported, set event callback for output stream should never fail");
+    auto res = stream->setEventCallback(new MockOutEventCallbacks);
+    EXPECT_RESULT(okOrNotSupported, res);
+    if (res == Result::OK) {
+        ASSERT_OK(stream->setEventCallback(nullptr));
+    } else {
+        doc::partialTest("The stream does not support event callback");
+    }
+}
diff --git a/current.txt b/current.txt
index 5f5758c..8e2016d 100644
--- a/current.txt
+++ b/current.txt
@@ -611,8 +611,9 @@
 bca5379d5065e2e08b6ad7308ffc8a71a972fc0698bec678ea32eea786d01cb5 android.hardware.audio@6.0::IPrimaryDevice
 fd1f1b29f26b42e886220f04a08086c00e5ade9d7b53f095438e578ab9d42a93 android.hardware.audio@6.0::IStream
 2df5d5866b37776f25079c0e54b54350a2abe4e025a59c9e02a7d3abe8ca00e8 android.hardware.audio@6.0::IStreamIn
-e6cd2b7c1a86b6ca683c0224ffde3b73aa14f6487de9f46833e539d26d1b3b5c android.hardware.audio@6.0::IStreamOut
+164826a380f4c1700183003f62d7532e367b67381c30ea44f946c0cf00008f85 android.hardware.audio@6.0::IStreamOut
 997fdaad7a9d17ee7e01feb7031a753e2365e72ad30b11d950e9183fabdf3844 android.hardware.audio@6.0::IStreamOutCallback
+e7ca0db9a1098210f327a9b152fa6afe6bf019c41e5264c64829d04d50c0a526 android.hardware.audio@6.0::IStreamOutEventCallback
 bee662c62d997d8065e2bcb5c1e7a9578931f22ce28fd02c219fdb4d0630abf7 android.hardware.audio.common@6.0::types
 817930d58412d662cb45e641c50cb62c727e4a3e3ffe7029a53cad9677b97d58 android.hardware.audio.effect@6.0::types
 525bec6b44f1103869c269a128d51b8dccd73af5340ba863c8886c68357c7faf android.hardware.audio.effect@6.0::IAcousticEchoCancelerEffect