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);
+};