Remove the format change broadcast

Whenever any audio endpoint became active, SarAsio had the driver send
KSEVENT_PINCAPS_FORMATCHANGE to every SAR filter on its next tick, and
the audio engine invalidated every stream open on a SAR endpoint. Its
check for SAR endpoints passes for any endpoint (IPropertyStore
returns S_OK and VT_EMPTY for a missing key), so starting a host
invalidated its own fresh streams, and so did every endpoint Windows
rebuilt and any other device appearing.

The event was added for #2, so the audio engine would re-read the
format of an endpoint recreated at a different sample rate. It wasn't
enough on Windows 10, whose format cache ignored it, so the driver
also puts the channel count, sample rate and sample size into each
endpoint's KS reference string there, which makes such an endpoint a
new one to Windows. With Windows 10 required, the event does nothing
useful. Remove it, SarAsio's endpoint notification client that only
existed to trigger it, the driver's SAR_SEND_FORMAT_CHANGE_EVENT IOCTL,
and SarConfigure's -u switch that sent it by hand.

On the test VM (16 endpoint pairs, three start/stop iterations), the
loopback run saw 34 to 116 stream invalidations per run with the
broadcast (3 runs) and none without it (8 runs). The format-* checks
(same endpoint IDs at 48 kHz, 96 kHz and 48 kHz again) pass with and
without it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: eiz

SarAsio/sarclient.cpp

@@ -43,13 +43,6 @@ void SarClient::tick(long bufferIndex)
     if (!_registers)
         return;
 
-    if (_updateSampleRateOnTick.exchange(false)) {
-        DWORD dummy;
-
-        DeviceIoControl(_device, SAR_SEND_FORMAT_CHANGE_EVENT,
-            nullptr, 0, nullptr, 0, &dummy, nullptr);
-    }
-
     // for each endpoint
     // read isActive, generation and buffer offset/size/position
     //   if offset/size invalid, skip endpoint (fill asio buffers with 0)
@@ -187,12 +180,6 @@ bool SarClient::start()
         return false;
     }
 
-    if (!openMmNotificationClient()) {
-        LOG(ERROR) << "Couldn't open MMDevice notification client";
-        stop();
-        return false;
-    }
-
     if (!setBufferLayout()) {
         LOG(ERROR) << "Couldn't set layout";
         stop();
@@ -214,21 +201,6 @@ bool SarClient::start()
 
 void SarClient::stop()
 {
-    if (_mmNotificationClientRegistered) {
-        _mmEnumerator->UnregisterEndpointNotificationCallback(
-            _mmNotificationClient);
-        _mmNotificationClientRegistered = false;
-    }
-
-    if (_mmNotificationClient) {
-        _mmNotificationClient->Release();
-        _mmNotificationClient = nullptr;
-    }
-
-    if (_mmEnumerator) {
-        _mmEnumerator = nullptr;
-    }
-
     if (_device != INVALID_HANDLE_VALUE) {
         _registersLock.lock();
         CancelIoEx(_device, nullptr);
@@ -327,34 +299,6 @@ bool SarClient::openControlDevice()
     return true;
 }
 
-bool SarClient::openMmNotificationClient()
-{
-    if (FAILED(CoCreateInstance(
-        __uuidof(MMDeviceEnumerator), nullptr, CLSCTX_ALL,
-        __uuidof(IMMDeviceEnumerator), (LPVOID *)&_mmEnumerator))) {
-
-        return false;
-    }
-
-    if (FAILED(CComObject<NotificationClient>::CreateInstance(
-        &_mmNotificationClient))) {
-
-        return false;
-    }
-
-    _mmNotificationClient->AddRef();
-    _mmNotificationClient->setClient(shared_from_this());
-
-    if (FAILED(_mmEnumerator->RegisterEndpointNotificationCallback(
-        _mmNotificationClient))) {
-
-        return false;
-    }
-
-    _mmNotificationClientRegistered = true;
-    return true;
-}
-
 bool SarClient::setBufferLayout()
 {
     SarSetBufferLayoutRequest request = {};
@@ -580,89 +524,4 @@ void SarClient::mux(
     }
 }
 
-HRESULT STDMETHODCALLTYPE SarClient::NotificationClient::OnDeviceStateChanged(
-    _In_  LPCWSTR pwstrDeviceId,
-    _In_  DWORD dwNewState)
-{
-    // When a SAR endpoint is re-activated after its initial creation, its
-    // supported sample rate may be different. To force the audio engine to
-    // notice the possible format change, we listen for device state change
-    // events and tell the kernel mode driver to broadcast a
-    // KSEVENT_PINCAPS_FORMATCHANGE event, which causes the audio engine to
-    // re-query the pin capabilities. This isn't needed for newly added
-    // endpoints or non-SAR endpoints, so we filter out those events.
-    if (dwNewState != DEVICE_STATE_ACTIVE) {
-        return S_OK;
-    }
-
-    if (auto client = _client.lock()) {
-        do {
-            CComPtr<IMMDeviceEnumerator> mmEnumerator;
-            CComPtr<IMMDevice> device;
-            CComPtr<IPropertyStore> ps;
-            PROPVARIANT pvalue = {};
-
-            // This seems a bit shady, but MSDN's device events example
-            // initializes COM the same way. It's not clear what the ownership
-            // of the thread that delivers the IMMNotificationClient events is.
-            CoInitialize(NULL);
-
-            if (FAILED(CoCreateInstance(
-                __uuidof(MMDeviceEnumerator), nullptr, CLSCTX_ALL,
-                __uuidof(IMMDeviceEnumerator), (LPVOID *)&mmEnumerator))) {
-
-                break;
-            }
-
-            if (FAILED(mmEnumerator->GetDevice(pwstrDeviceId, &device))) {
-                break;
-            }
-
-            if (FAILED(device->OpenPropertyStore(STGM_READ, &ps))) {
-                break;
-            }
-
-            if (FAILED(ps->GetValue(
-                PKEY_SynchronousAudioRouter_EndpointId, &pvalue))) {
-
-                break;
-            }
-
-            client->updateSampleRateOnTick();
-            PropVariantClear(&pvalue);
-        } while(false);
-
-        CoUninitialize();
-    }
-
-    return S_OK;
-}
-
-HRESULT STDMETHODCALLTYPE SarClient::NotificationClient::OnDeviceAdded(
-    _In_  LPCWSTR pwstrDeviceId)
-{
-    return S_OK;
-}
-
-HRESULT STDMETHODCALLTYPE SarClient::NotificationClient::OnDeviceRemoved(
-    _In_  LPCWSTR pwstrDeviceId)
-{
-    return S_OK;
-}
-
-HRESULT STDMETHODCALLTYPE SarClient::NotificationClient::OnDefaultDeviceChanged(
-    _In_  EDataFlow flow,
-    _In_  ERole role,
-    _In_  LPCWSTR pwstrDefaultDeviceId)
-{
-    return S_OK;
-}
-
-HRESULT STDMETHODCALLTYPE SarClient::NotificationClient::OnPropertyValueChanged(
-    _In_  LPCWSTR pwstrDeviceId,
-    _In_  const PROPERTYKEY key)
-{
-    return S_OK;
-}
-
 } // namespace Sar

SarAsio/sarclient.h

@@ -39,10 +39,6 @@ struct SarClient: public std::enable_shared_from_this<SarClient>
     void tick(long bufferIndex);
     bool start();
     void stop();
-    void updateSampleRateOnTick()
-    {
-        _updateSampleRateOnTick = true;
-    }
 
 private:
     struct NotificationHandle
@@ -64,42 +60,7 @@ struct SarClient: public std::enable_shared_from_this<SarClient>
         SarHandleQueueResponse responses[32];
     };
 
-    struct ATL_NO_VTABLE NotificationClient:
-        public CComObjectRootEx<CComMultiThreadModel>,
-        public IMMNotificationClient
-    {
-        BEGIN_COM_MAP(NotificationClient)
-            COM_INTERFACE_ENTRY(IMMNotificationClient)
-        END_COM_MAP()
-
-        DECLARE_NO_REGISTRY()
-
-        void setClient(std::weak_ptr<SarClient> client)
-        {
-            _client = client;
-        }
-
-        virtual HRESULT STDMETHODCALLTYPE OnDeviceStateChanged(
-            _In_  LPCWSTR pwstrDeviceId,
-            _In_  DWORD dwNewState) override;
-        virtual HRESULT STDMETHODCALLTYPE OnDeviceAdded(
-            _In_  LPCWSTR pwstrDeviceId) override;
-        virtual HRESULT STDMETHODCALLTYPE OnDeviceRemoved(
-            _In_  LPCWSTR pwstrDeviceId) override;
-        virtual HRESULT STDMETHODCALLTYPE OnDefaultDeviceChanged(
-            _In_  EDataFlow flow,
-            _In_  ERole role,
-            _In_  LPCWSTR pwstrDefaultDeviceId) override;
-        virtual HRESULT STDMETHODCALLTYPE OnPropertyValueChanged(
-            _In_  LPCWSTR pwstrDeviceId,
-            _In_  const PROPERTYKEY key) override;
-
-    private:
-        std::weak_ptr<SarClient> _client;
-    };
-
     bool openControlDevice();
-    bool openMmNotificationClient();
     bool setBufferLayout();
     bool createEndpoints();
     bool enableRegistryFilter();
@@ -127,10 +88,6 @@ struct SarClient: public std::enable_shared_from_this<SarClient>
     volatile SarEndpointRegisters *_registers;
     HandleQueueCompletion _handleQueueCompletion;
     bool _handleQueueStarted;
-    CComPtr<IMMDeviceEnumerator> _mmEnumerator;
-    CComObject<NotificationClient> *_mmNotificationClient = nullptr;
-    bool _mmNotificationClientRegistered = false;
-    std::atomic<bool> _updateSampleRateOnTick = false;
     std::mutex _registersLock;
 };
 

SarConfigure/SarConfigure.cpp

@@ -59,89 +59,21 @@ static int openConfigurationDialog(Sar::AsioDriver& driver) {
     }
 }
 
-static bool broadcastPinFormatChange() {
-    HDEVINFO devinfo;
-    SP_DEVICE_INTERFACE_DATA interfaceData;
-    PSP_DEVICE_INTERFACE_DETAIL_DATA interfaceDetail;
-    DWORD requiredSize;
-    HANDLE _device;
-    DWORD dummy;
-
-    interfaceData.cbSize = sizeof(SP_DEVICE_INTERFACE_DATA);
-    devinfo = SetupDiGetClassDevs(
-        &GUID_DEVINTERFACE_SYNCHRONOUSAUDIOROUTER, nullptr, nullptr,
-        DIGCF_DEVICEINTERFACE | DIGCF_PRESENT);
-
-    if (devinfo == INVALID_HANDLE_VALUE) {
-        return false;
-    }
-
-    if (!SetupDiEnumDeviceInterfaces(devinfo, NULL,
-        &GUID_DEVINTERFACE_SYNCHRONOUSAUDIOROUTER, 0, &interfaceData)) {
-
-        return false;
-    }
-
-    SetLastError(0);
-    SetupDiGetDeviceInterfaceDetail(
-        devinfo, &interfaceData, nullptr, 0, &requiredSize, nullptr);
-
-    if (GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
-        return false;
-    }
-
-    interfaceDetail = (PSP_DEVICE_INTERFACE_DETAIL_DATA)malloc(requiredSize);
-    interfaceDetail->cbSize = sizeof(SP_DEVICE_INTERFACE_DETAIL_DATA);
-
-    if (!SetupDiGetDeviceInterfaceDetail(
-        devinfo, &interfaceData, interfaceDetail,
-        requiredSize, nullptr, nullptr)) {
-
-        free(interfaceDetail);
-        return false;
-    }
-
-    _device = CreateFile(interfaceDetail->DevicePath,
-        GENERIC_ALL, 0, nullptr, OPEN_EXISTING,
-        FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED, nullptr);
-
-    if (_device == INVALID_HANDLE_VALUE) {
-        free(interfaceDetail);
-        return false;
-    }
-
-    free(interfaceDetail);
-
-    DeviceIoControl(_device, SAR_SEND_FORMAT_CHANGE_EVENT,
-        nullptr, 0, nullptr, 0, &dummy, nullptr);
-    printf("Sent SAR_SEND_FORMAT_CHANGE_EVENT\n");
-
-    CloseHandle(_device);
-
-    return true;
-}
-
 int main(int argc, char *argv[])
 {
+    CoInitialize(NULL);
 
-    if (argc >= 2 && !strcmp(argv[1], "-u")) {
-        broadcastPinFormatChange();
-    }
-    else {
-        CoInitialize(NULL);
-
-        std::vector<Sar::AsioDriver> asioDrivers = Sar::InstalledAsioDrivers();
+    std::vector<Sar::AsioDriver> asioDrivers = Sar::InstalledAsioDrivers();
 
-        printf("\n");
-        for (size_t i = 0; i < asioDrivers.size(); i++) {
-            printf("Checking driver: %s == %s\n", asioDrivers[i].clsid.c_str(), CLSID_STR_SynchronousAudioRouter);
-            if (asioDrivers[i].clsid == CLSID_STR_SynchronousAudioRouter) {
-                Sar::AsioDriver& driver = asioDrivers[i];
-                printf("Found SAR ASIO driver: %s\n", driver.name.c_str());
-                return openConfigurationDialog(driver);
-            }
+    printf("\n");
+    for (size_t i = 0; i < asioDrivers.size(); i++) {
+        printf("Checking driver: %s == %s\n", asioDrivers[i].clsid.c_str(), CLSID_STR_SynchronousAudioRouter);
+        if (asioDrivers[i].clsid == CLSID_STR_SynchronousAudioRouter) {
+            Sar::AsioDriver& driver = asioDrivers[i];
+            printf("Found SAR ASIO driver: %s\n", driver.name.c_str());
+            return openConfigurationDialog(driver);
         }
-
-        CoUninitialize();
     }
+
+    CoUninitialize();
 }

SarTest/wasapi.h

@@ -99,9 +99,10 @@ struct WasapiOptions
     bool expectInvalidation = false;
     double minValidRatio = 0.5;
     long long maxDiscontinuities = -1;   // -1: report only
-    // SarAsio broadcasts a format change whenever one of its endpoints
-    // becomes active, which invalidates open streams: wait before streaming,
-    // and reopen invalidated streams like a well-behaved client would.
+    // Streams opened just as a host's endpoints appear can be invalidated
+    // (SarAsio used to broadcast a format change on every endpoint
+    // activation): wait before streaming, and reopen invalidated streams like
+    // a well-behaved client would.
     double settleSeconds = 2.0;
     int maxReopens = 20;
     long long maxTransitionFrames = 4800;