diff --git a/audio/aidl/default/deprecated/StreamSwitcher.cpp b/audio/aidl/default/deprecated/StreamSwitcher.cpp
new file mode 100644
index 0000000..f1e0f52
--- /dev/null
+++ b/audio/aidl/default/deprecated/StreamSwitcher.cpp
@@ -0,0 +1,271 @@
+/*
+ * Copyright (C) 2023 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.
+ */
+
+#include <limits>
+
+#define LOG_TAG "AHAL_StreamSwitcher"
+
+#include <Utils.h>
+#include <android-base/logging.h>
+#include <error/expected_utils.h>
+
+#include "core-impl/StreamStub.h"
+#include "deprecated/StreamSwitcher.h"
+
+using aidl::android::hardware::audio::effect::IEffect;
+using aidl::android::media::audio::common::AudioDevice;
+
+namespace aidl::android::hardware::audio::core::deprecated {
+
+StreamSwitcher::StreamSwitcher(StreamContext* context, const Metadata& metadata)
+    : mContext(context),
+      mMetadata(metadata),
+      mStream(new InnerStreamWrapper<StreamStub>(context, mMetadata)) {}
+
+ndk::ScopedAStatus StreamSwitcher::closeCurrentStream(bool validateStreamState) {
+    if (!mStream) return ndk::ScopedAStatus::ok();
+    RETURN_STATUS_IF_ERROR(mStream->prepareToClose());
+    RETURN_STATUS_IF_ERROR(mStream->close());
+    if (validateStreamState && !isValidClosingStreamState(mStream->getStatePriorToClosing())) {
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    mStream.reset();
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::close() {
+    if (mStream != nullptr) {
+        auto status = closeCurrentStream(false /*validateStreamState*/);
+        // The actual state is irrelevant since only StreamSwitcher cares about it.
+        onClose(StreamDescriptor::State::STANDBY);
+        return status;
+    }
+    LOG(ERROR) << __func__ << ": stream was already closed";
+    return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+}
+
+ndk::ScopedAStatus StreamSwitcher::prepareToClose() {
+    if (mStream != nullptr) {
+        return mStream->prepareToClose();
+    }
+    LOG(ERROR) << __func__ << ": stream was closed";
+    return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+}
+
+ndk::ScopedAStatus StreamSwitcher::updateHwAvSyncId(int32_t in_hwAvSyncId) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    RETURN_STATUS_IF_ERROR(mStream->updateHwAvSyncId(in_hwAvSyncId));
+    mHwAvSyncId = in_hwAvSyncId;
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::getVendorParameters(const std::vector<std::string>& in_ids,
+                                                       std::vector<VendorParameter>* _aidl_return) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    if (mIsStubStream) {
+        LOG(ERROR) << __func__ << ": the stream is not connected";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    return mStream->getVendorParameters(in_ids, _aidl_return);
+}
+
+ndk::ScopedAStatus StreamSwitcher::setVendorParameters(
+        const std::vector<VendorParameter>& in_parameters, bool in_async) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    if (mIsStubStream) {
+        mMissedParameters.emplace_back(in_parameters, in_async);
+        return ndk::ScopedAStatus::ok();
+    }
+    return mStream->setVendorParameters(in_parameters, in_async);
+}
+
+ndk::ScopedAStatus StreamSwitcher::addEffect(const std::shared_ptr<IEffect>& in_effect) {
+    if (in_effect == nullptr) {
+        LOG(DEBUG) << __func__ << ": null effect";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+    }
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    if (!mIsStubStream) {
+        RETURN_STATUS_IF_ERROR(mStream->addEffect(in_effect));
+    }
+    mEffects.push_back(in_effect);
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::removeEffect(const std::shared_ptr<IEffect>& in_effect) {
+    if (in_effect == nullptr) {
+        LOG(DEBUG) << __func__ << ": null effect";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+    }
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    for (auto it = mEffects.begin(); it != mEffects.end(); ++it) {
+        if ((*it)->asBinder() == in_effect->asBinder()) {
+            mEffects.erase(it);
+            break;
+        }
+    }
+    return !mIsStubStream ? mStream->removeEffect(in_effect) : ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::getStreamCommonCommon(
+        std::shared_ptr<IStreamCommon>* _aidl_return) {
+    if (!mCommon) {
+        LOG(FATAL) << __func__ << ": the common interface was not created";
+    }
+    *_aidl_return = mCommon.getInstance();
+    LOG(DEBUG) << __func__ << ": returning " << _aidl_return->get()->asBinder().get();
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::updateMetadataCommon(const Metadata& metadata) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    mMetadata = metadata;
+    return !mIsStubStream ? mStream->updateMetadataCommon(metadata) : ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::initInstance(
+        const std::shared_ptr<StreamCommonInterface>& delegate) {
+    mCommon = ndk::SharedRefBase::make<StreamCommonDelegator>(delegate);
+    // The delegate is null because StreamSwitcher handles IStreamCommon methods by itself.
+    return mStream->initInstance(nullptr);
+}
+
+const StreamContext& StreamSwitcher::getContext() const {
+    return *mContext;
+}
+
+bool StreamSwitcher::isClosed() const {
+    return mStream == nullptr || mStream->isClosed();
+}
+
+const StreamCommonInterface::ConnectedDevices& StreamSwitcher::getConnectedDevices() const {
+    return mStream->getConnectedDevices();
+}
+
+ndk::ScopedAStatus StreamSwitcher::setConnectedDevices(const std::vector<AudioDevice>& devices) {
+    LOG(DEBUG) << __func__ << ": " << ::android::internal::ToString(devices);
+    if (mStream->getConnectedDevices() == devices) return ndk::ScopedAStatus::ok();
+    const DeviceSwitchBehavior behavior = switchCurrentStream(devices);
+    if (behavior == DeviceSwitchBehavior::UNSUPPORTED_DEVICES) {
+        return ndk::ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+    } else if (behavior == DeviceSwitchBehavior::SWITCH_TO_STUB_STREAM && !devices.empty()) {
+        // This is an error in the extending class.
+        LOG(FATAL) << __func__
+                   << ": switching to stub stream with connected devices is not allowed";
+    }
+    if (behavior == USE_CURRENT_STREAM) {
+        mIsStubStream = false;
+    } else {
+        LOG(DEBUG) << __func__ << ": connected devices changed, switching stream";
+        // Two streams can't be opened for the same context, thus we always need to close
+        // the current one before creating a new one.
+        RETURN_STATUS_IF_ERROR(closeCurrentStream(true /*validateStreamState*/));
+        if (behavior == CREATE_NEW_STREAM) {
+            mStream = createNewStream(devices, mContext, mMetadata);
+            mIsStubStream = false;
+        } else {  // SWITCH_TO_STUB_STREAM
+            mStream.reset(new InnerStreamWrapper<StreamStub>(mContext, mMetadata));
+            mIsStubStream = true;
+        }
+        // The delegate is null because StreamSwitcher handles IStreamCommon methods by itself.
+        if (ndk::ScopedAStatus status = mStream->initInstance(nullptr); !status.isOk()) {
+            if (mIsStubStream) {
+                LOG(FATAL) << __func__
+                           << ": failed to initialize stub stream: " << status.getDescription();
+            }
+            // Need to close the current failed stream, and report an error.
+            // Since we can't operate without a stream implementation, put a stub in.
+            RETURN_STATUS_IF_ERROR(closeCurrentStream(false /*validateStreamState*/));
+            mStream.reset(new InnerStreamWrapper<StreamStub>(mContext, mMetadata));
+            (void)mStream->initInstance(nullptr);
+            (void)mStream->setConnectedDevices(devices);
+            return status;
+        }
+    }
+    RETURN_STATUS_IF_ERROR(mStream->setConnectedDevices(devices));
+    if (behavior == CREATE_NEW_STREAM) {
+        // These updates are less critical, only log warning on failure.
+        if (mHwAvSyncId.has_value()) {
+            if (auto status = mStream->updateHwAvSyncId(*mHwAvSyncId); !status.isOk()) {
+                LOG(WARNING) << __func__ << ": could not update HW AV Sync for a new stream: "
+                             << status.getDescription();
+            }
+        }
+        for (const auto& vndParam : mMissedParameters) {
+            if (auto status = mStream->setVendorParameters(vndParam.first, vndParam.second);
+                !status.isOk()) {
+                LOG(WARNING) << __func__ << ": error while setting parameters for a new stream: "
+                             << status.getDescription();
+            }
+        }
+        mMissedParameters.clear();
+        for (const auto& effect : mEffects) {
+            if (auto status = mStream->addEffect(effect); !status.isOk()) {
+                LOG(WARNING) << __func__ << ": error while adding effect for a new stream: "
+                             << status.getDescription();
+            }
+        }
+        if (mBluetoothParametersUpdated) {
+            if (auto status = mStream->bluetoothParametersUpdated(); !status.isOk()) {
+                LOG(WARNING) << __func__
+                             << ": error while updating BT parameters for a new stream: "
+                             << status.getDescription();
+            }
+        }
+        mBluetoothParametersUpdated = false;
+    }
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::bluetoothParametersUpdated() {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    if (mIsStubStream) {
+        mBluetoothParametersUpdated = true;
+        return ndk::ScopedAStatus::ok();
+    }
+    return mStream->bluetoothParametersUpdated();
+}
+
+ndk::ScopedAStatus StreamSwitcher::setGain(float gain) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    return mStream->setGain(gain);
+}
+
+}  // namespace aidl::android::hardware::audio::core::deprecated
diff --git a/audio/aidl/default/deprecated/StreamSwitcher.h b/audio/aidl/default/deprecated/StreamSwitcher.h
new file mode 100644
index 0000000..56fdd23
--- /dev/null
+++ b/audio/aidl/default/deprecated/StreamSwitcher.h
@@ -0,0 +1,202 @@
+/*
+ * Copyright (C) 2023 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.
+ */
+
+/**
+ ** This class is deprecated because its use causes threading issues
+ ** with the FMQ due to change of threads reading and writing into FMQ.
+ **
+ ** DO NOT USE. These files will be removed.
+ **/
+
+#pragma once
+
+#include "core-impl/Stream.h"
+
+namespace aidl::android::hardware::audio::core::deprecated {
+
+// 'StreamSwitcher' is an implementation of 'StreamCommonInterface' which allows
+// dynamically switching the underlying stream implementation based on currently
+// connected devices. This is achieved by replacing inheritance from
+// 'StreamCommonImpl' with owning an instance of it. StreamSwitcher must be
+// extended in order to supply the logic for choosing the stream
+// implementation. When there are no connected devices, for instance, upon the
+// creation, the StreamSwitcher engages an instance of a stub stream in order to
+// keep serving requests coming via 'StreamDescriptor'.
+//
+// StreamSwitcher implements the 'IStreamCommon' interface directly, with
+// necessary delegation to the current stream implementation. While the stub
+// stream is engaged, any requests made via 'IStreamCommon' (parameters, effects
+// setting, etc) are postponed and only delivered on device connection change
+// to the "real" stream implementation provided by the extending class. This is why
+// the behavior of StreamSwitcher in the "stub" state is not identical to behavior
+// of 'StreamStub'. It can become a full substitute for 'StreamStub' once
+// device connection change event occurs and the extending class returns
+// 'LEAVE_CURRENT_STREAM' from 'switchCurrentStream' method.
+//
+// There is a natural limitation that the current stream implementation may only
+// be switched when the stream is in the 'STANDBY' state. Thus, when the event
+// to switch the stream occurs, the current stream is stopped and joined, and
+// its last state is validated. Since the change of the set of connected devices
+// normally occurs on patch updates, if the stream was not in standby, this is
+// reported to the caller of 'IModule.setAudioPatch' as the 'EX_ILLEGAL_STATE'
+// error.
+//
+// The simplest use case, when the implementor just needs to emulate the legacy HAL API
+// behavior of receiving the connected devices upon stream creation, the implementation
+// of the extending class can look as follows. We assume that 'StreamLegacy' implementation
+// is the one requiring to know connected devices on creation:
+//
+//   class StreamLegacy : public StreamCommonImpl {
+//     public:
+//       StreamLegacy(StreamContext* context, const Metadata& metadata,
+//                    const std::vector<AudioDevice>& devices);
+//   };
+//
+//   class StreamOutLegacy final : public StreamOut, public StreamSwitcher {
+//     public:
+//       StreamOutLegacy(StreamContext&& context, metatadata etc.)
+//     private:
+//       DeviceSwitchBehavior switchCurrentStream(const std::vector<AudioDevice>&) override {
+//           // This implementation effectively postpones stream creation until
+//           // receiving the first call to 'setConnectedDevices' with a non-empty list.
+//           return isStubStream() ? DeviceSwitchBehavior::CREATE_NEW_STREAM :
+//               DeviceSwitchBehavior::USE_CURRENT_STREAM;
+//       }
+//       std::unique_ptr<StreamCommonInterfaceEx> createNewStream(
+//               const std::vector<AudioDevice>& devices,
+//               StreamContext* context, const Metadata& metadata) override {
+//           return std::unique_ptr<StreamCommonInterfaceEx>(new InnerStreamWrapper<StreamLegacy>(
+//               context, metadata, devices));
+//       }
+//       void onClose(StreamDescriptor::State) override { defaultOnClose(); }
+//   }
+//
+
+class StreamCommonInterfaceEx : virtual public StreamCommonInterface {
+  public:
+    virtual StreamDescriptor::State getStatePriorToClosing() const = 0;
+};
+
+template <typename T>
+class InnerStreamWrapper : public T, public StreamCommonInterfaceEx {
+  public:
+    template <typename... Args>
+    InnerStreamWrapper(Args&&... args) : T(std::forward<Args>(args)...) {}
+    StreamDescriptor::State getStatePriorToClosing() const override { return mStatePriorToClosing; }
+
+  private:
+    // Do not need to do anything on close notification from the inner stream
+    // because StreamSwitcher handles IStreamCommon::close by itself.
+    void onClose(StreamDescriptor::State statePriorToClosing) override {
+        mStatePriorToClosing = statePriorToClosing;
+    }
+
+    StreamDescriptor::State mStatePriorToClosing = StreamDescriptor::State::STANDBY;
+};
+
+class StreamSwitcher : virtual public StreamCommonInterface {
+  public:
+    StreamSwitcher(StreamContext* context, const Metadata& metadata);
+
+    ndk::ScopedAStatus close() override;
+    ndk::ScopedAStatus prepareToClose() override;
+    ndk::ScopedAStatus updateHwAvSyncId(int32_t in_hwAvSyncId) override;
+    ndk::ScopedAStatus getVendorParameters(const std::vector<std::string>& in_ids,
+                                           std::vector<VendorParameter>* _aidl_return) override;
+    ndk::ScopedAStatus setVendorParameters(const std::vector<VendorParameter>& in_parameters,
+                                           bool in_async) override;
+    ndk::ScopedAStatus addEffect(
+            const std::shared_ptr<::aidl::android::hardware::audio::effect::IEffect>& in_effect)
+            override;
+    ndk::ScopedAStatus removeEffect(
+            const std::shared_ptr<::aidl::android::hardware::audio::effect::IEffect>& in_effect)
+            override;
+
+    ndk::ScopedAStatus getStreamCommonCommon(std::shared_ptr<IStreamCommon>* _aidl_return) override;
+    ndk::ScopedAStatus updateMetadataCommon(const Metadata& metadata) override;
+
+    ndk::ScopedAStatus initInstance(
+            const std::shared_ptr<StreamCommonInterface>& delegate) override;
+    const StreamContext& getContext() const override;
+    bool isClosed() const override;
+    const ConnectedDevices& getConnectedDevices() const override;
+    ndk::ScopedAStatus setConnectedDevices(
+            const std::vector<::aidl::android::media::audio::common::AudioDevice>& devices)
+            override;
+    ndk::ScopedAStatus bluetoothParametersUpdated() override;
+    ndk::ScopedAStatus setGain(float gain) override;
+
+  protected:
+    // Since switching a stream requires closing down the current stream, StreamSwitcher
+    // asks the extending class its intent on the connected devices change.
+    enum DeviceSwitchBehavior {
+        // Continue using the current stream implementation. If it's the stub implementation,
+        // StreamSwitcher starts treating the stub stream as a "real" implementation,
+        // without effectively closing it and starting again.
+        USE_CURRENT_STREAM,
+        // This is the normal case when the extending class provides a "real" implementation
+        // which is not a stub implementation.
+        CREATE_NEW_STREAM,
+        // This is the case when the extending class wants to revert back to the initial
+        // condition of using a stub stream provided by the StreamSwitcher. This behavior
+        // is only allowed when the list of connected devices is empty.
+        SWITCH_TO_STUB_STREAM,
+        // Use when the set of devices is not supported by the extending class. This returns
+        // 'EX_UNSUPPORTED_OPERATION' from 'setConnectedDevices'.
+        UNSUPPORTED_DEVICES,
+    };
+    // StreamSwitcher will call these methods from 'setConnectedDevices'. If the switch behavior
+    // is 'CREATE_NEW_STREAM', the 'createwNewStream' function will be called (with the same
+    // device vector) for obtaining a new stream implementation, assuming that closing
+    // the current stream was a success.
+    virtual DeviceSwitchBehavior switchCurrentStream(
+            const std::vector<::aidl::android::media::audio::common::AudioDevice>& devices) = 0;
+    virtual std::unique_ptr<StreamCommonInterfaceEx> createNewStream(
+            const std::vector<::aidl::android::media::audio::common::AudioDevice>& devices,
+            StreamContext* context, const Metadata& metadata) = 0;
+    virtual void onClose(StreamDescriptor::State streamPriorToClosing) = 0;
+
+    bool isStubStream() const { return mIsStubStream; }
+    StreamCommonInterfaceEx* getCurrentStream() const { return mStream.get(); }
+
+  private:
+    using VndParam = std::pair<std::vector<VendorParameter>, bool /*isAsync*/>;
+
+    static constexpr bool isValidClosingStreamState(StreamDescriptor::State state) {
+        return state == StreamDescriptor::State::STANDBY || state == StreamDescriptor::State::ERROR;
+    }
+
+    ndk::ScopedAStatus closeCurrentStream(bool validateStreamState);
+
+    // StreamSwitcher does not own the context.
+    StreamContext* mContext;
+    Metadata mMetadata;
+    ChildInterface<StreamCommonDelegator> mCommon;
+    // The current stream.
+    std::unique_ptr<StreamCommonInterfaceEx> mStream;
+    // Indicates whether 'mCurrentStream' is a stub stream implementation
+    // maintained by StreamSwitcher until the extending class provides a "real"
+    // implementation. The invariant of this state is that there are no connected
+    // devices.
+    bool mIsStubStream = true;
+    // Storage for the data from commands received via 'IStreamCommon'.
+    std::optional<int32_t> mHwAvSyncId;
+    std::vector<VndParam> mMissedParameters;
+    std::vector<std::shared_ptr<::aidl::android::hardware::audio::effect::IEffect>> mEffects;
+    bool mBluetoothParametersUpdated = false;
+};
+
+}  // namespace aidl::android::hardware::audio::core::deprecated