Add audio engine warm-up on Windows

Current implementation has the following audio problem on Windows: if
any of the classes that support audio playback are used (QMediaPlayer
or QSoundEffect) sound is cutting off (part of the sound is missing
usually beginning). If there're some other applications playing sounds
in the system while we try to play our sound then everyting works fine.
Apparently this happens due to warm up delays for system audio engine
and if there're other applications available they're simply keeping it
alive and it's already fully initialized and ready to be used by us
when we need it.

As a workaround to this problem an unused audio device is created that
is fully initialized and set to play (nothing) but is actually present
for any subsequently created audio devices that are ready from the
start without any delays.

Pick-to: 6.5
Task-number: QTBUG-112512
Change-Id: I660a48e8ac1a1ebd1cfb6a9ff76605c3b4742e17
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
Reviewed-by: Lars Knoll <lars@knoll.priv.no>
Reviewed-by: Jøger Hansegård <joger.hansegard@qt.io>

10 files changed, 157 insertions, 4 deletions

diff --git a/src/multimedia/CMakeLists.txt b/src/multimedia/CMakeLists.txt
index 089d88c8e..1cdbd5927 100644
--- a/src/multimedia/CMakeLists.txt
+++ b/src/multimedia/CMakeLists.txt
@@ -214,6 +214,7 @@ qt_internal_extend_target(Multimedia CONDITION QT_FEATURE_wmf
         windows/qwindowsmultimediautils.cpp windows/qwindowsmultimediautils_p.h
         windows/qwindowsmfdefs.cpp windows/qwindowsmfdefs_p.h
         windows/qcomptr_p.h
+        windows/qcomtaskresource_p.h
     INCLUDE_DIRECTORIES
         windows
     LIBRARIES
@@ -235,6 +236,7 @@ qt_internal_extend_target(Multimedia CONDITION QT_FEATURE_wmf AND MINGW
         windows/qwindowsmultimediautils.cpp windows/qwindowsmultimediautils_p.h
         windows/qwindowsmfdefs.cpp windows/qwindowsmfdefs_p.h
         windows/qcomptr_p.h
+        windows/qcomtaskresource_p.h
 )
 
 qt_internal_extend_target(Multimedia CONDITION WASM
diff --git a/src/multimedia/audio/qaudiosystem.cpp b/src/multimedia/audio/qaudiosystem.cpp
index ef7552492..b052b78a6 100644
--- a/src/multimedia/audio/qaudiosystem.cpp
+++ b/src/multimedia/audio/qaudiosystem.cpp
@@ -3,9 +3,14 @@
 
 #include "qaudiosystem_p.h"
 
+#include <private/qplatformmediadevices_p.h>
+
 QT_BEGIN_NAMESPACE
 
-QPlatformAudioSink::QPlatformAudioSink(QObject *parent) : QObject(parent) { }
+QPlatformAudioSink::QPlatformAudioSink(QObject *parent) : QObject(parent)
+{
+    QPlatformMediaDevices::instance()->prepareAudio();
+}
 
 qreal QPlatformAudioSink::volume() const
 {
diff --git a/src/multimedia/audio/qsoundeffect.cpp b/src/multimedia/audio/qsoundeffect.cpp
index b6b6f2d1f..d65df2502 100644
--- a/src/multimedia/audio/qsoundeffect.cpp
+++ b/src/multimedia/audio/qsoundeffect.cpp
@@ -8,6 +8,7 @@
 #include "qaudiosink.h"
 #include "qmediadevices.h"
 #include <QtCore/qloggingcategory.h>
+#include <private/qplatformmediadevices_p.h>
 
 static Q_LOGGING_CATEGORY(qLcSoundEffect, "qt.multimedia.soundeffect")
 
@@ -72,6 +73,8 @@ QSoundEffectPrivate::QSoundEffectPrivate(QSoundEffect *q, const QAudioDevice &au
     , m_audioDevice(audioDevice)
 {
     open(QIODevice::ReadOnly);
+
+    QPlatformMediaDevices::instance()->prepareAudio();
 }
 
 void QSoundEffectPrivate::sampleReady()
diff --git a/src/multimedia/platform/qplatformmediadevices.cpp b/src/multimedia/platform/qplatformmediadevices.cpp
index 03f1af75e..95cf3b7a0 100644
--- a/src/multimedia/platform/qplatformmediadevices.cpp
+++ b/src/multimedia/platform/qplatformmediadevices.cpp
@@ -153,5 +153,6 @@ void QPlatformMediaDevices::videoInputsChanged() const
         emit m->videoInputsChanged();
 }
 
+void QPlatformMediaDevices::prepareAudio() { }
 
 QT_END_NAMESPACE
diff --git a/src/multimedia/platform/qplatformmediadevices_p.h b/src/multimedia/platform/qplatformmediadevices_p.h
index 3cde651fa..9b8d0d5e7 100644
--- a/src/multimedia/platform/qplatformmediadevices_p.h
+++ b/src/multimedia/platform/qplatformmediadevices_p.h
@@ -62,6 +62,8 @@ public:
 
     void videoInputsChanged() const;
 
+    virtual void prepareAudio();
+
 protected:
     void audioInputsChanged() const;
     void audioOutputsChanged() const;
diff --git a/src/multimedia/platform/qplatformmediaplayer.cpp b/src/multimedia/platform/qplatformmediaplayer.cpp
index 76de92cff..310776c8a 100644
--- a/src/multimedia/platform/qplatformmediaplayer.cpp
+++ b/src/multimedia/platform/qplatformmediaplayer.cpp
@@ -4,9 +4,15 @@
 #include "qplatformmediaplayer_p.h"
 #include <private/qmediaplayer_p.h>
 #include "qmediaplayer.h"
+#include "qplatformmediadevices_p.h"
 
 QT_BEGIN_NAMESPACE
 
+QPlatformMediaPlayer::QPlatformMediaPlayer(QMediaPlayer *parent) : player(parent)
+{
+    QPlatformMediaDevices::instance()->prepareAudio();
+}
+
 QPlatformMediaPlayer::~QPlatformMediaPlayer()
 {
 }
diff --git a/src/multimedia/platform/qplatformmediaplayer_p.h b/src/multimedia/platform/qplatformmediaplayer_p.h
index b2cd5e571..b31cbac89 100644
--- a/src/multimedia/platform/qplatformmediaplayer_p.h
+++ b/src/multimedia/platform/qplatformmediaplayer_p.h
@@ -125,9 +125,8 @@ public:
     }
 
 protected:
-    explicit QPlatformMediaPlayer(QMediaPlayer *parent = nullptr)
-        : player(parent)
-    {}
+    explicit QPlatformMediaPlayer(QMediaPlayer *parent = nullptr);
+
 private:
     QMediaPlayer *player = nullptr;
     QMediaPlayer::MediaStatus m_status = QMediaPlayer::NoMedia;
diff --git a/src/multimedia/windows/qcomtaskresource_p.h b/src/multimedia/windows/qcomtaskresource_p.h
new file mode 100644
index 000000000..7d3fd46ba
--- /dev/null
+++ b/src/multimedia/windows/qcomtaskresource_p.h
@@ -0,0 +1,57 @@
+// Copyright (C) 2023 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. It exists purely as an
+// implementation detail. This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#ifndef QCOMTASKRESOURCE_P_H
+#define QCOMTASKRESOURCE_P_H
+
+#include <QtCore/qassert.h>
+
+#include <objbase.h>
+#include <utility>
+
+template<typename T>
+class QComTaskResource final
+{
+public:
+    QComTaskResource() = default;
+    explicit QComTaskResource(T *resource) : m_resource(resource) { }
+    ~QComTaskResource() { reset(); }
+
+    QComTaskResource(const QComTaskResource<T> &source) = delete;
+    QComTaskResource &operator=(const QComTaskResource<T> &right) = delete;
+
+    explicit operator bool() const { return m_resource != nullptr; }
+    T *operator->() const { return m_resource; }
+
+    T **address()
+    {
+        Q_ASSERT(m_resource == nullptr);
+        return &m_resource;
+    }
+    T *get() const { return m_resource; }
+    T *release() { return std::exchange(m_resource, nullptr); }
+    void reset(T *resource = nullptr)
+    {
+        if (m_resource != resource) {
+            if (m_resource)
+                CoTaskMemFree(m_resource);
+            m_resource = resource;
+        }
+    }
+
+private:
+    T *m_resource = nullptr;
+};
+
+#endif
diff --git a/src/multimedia/windows/qwindowsmediadevices.cpp b/src/multimedia/windows/qwindowsmediadevices.cpp
index 9dd2db383..c6c2b68df 100644
--- a/src/multimedia/windows/qwindowsmediadevices.cpp
+++ b/src/multimedia/windows/qwindowsmediadevices.cpp
@@ -8,6 +8,7 @@
 #include "qwindowsaudiosource_p.h"
 #include "qwindowsaudiosink_p.h"
 #include "qwindowsaudiodevice_p.h"
+#include "qcomtaskresource_p.h"
 
 #include <mmsystem.h>
 #include <mmddk.h>
@@ -191,9 +192,16 @@ QWindowsMediaDevices::~QWindowsMediaDevices()
     if (m_deviceEnumerator) {
         m_deviceEnumerator->UnregisterEndpointNotificationCallback(m_notificationClient.get());
     }
+    if (m_warmUpAudioClient) {
+        HRESULT hr = m_warmUpAudioClient->Stop();
+        if (FAILED(hr)) {
+            qWarning() << "Failed to stop audio engine" << hr;
+        }
+    }
 
     m_deviceEnumerator.reset();
     m_notificationClient.reset();
+    m_warmUpAudioClient.reset();
 
     CoUninitialize();
 }
@@ -285,4 +293,67 @@ QPlatformAudioSink *QWindowsMediaDevices::createAudioSink(const QAudioDevice &de
     return new QWindowsAudioSink(devInfo->immDev(), parent);
 }
 
+void QWindowsMediaDevices::prepareAudio()
+{
+    if (m_isAudioClientWarmedUp.exchange(true))
+        return;
+
+    QComPtr<IMMDeviceEnumerator> deviceEnumerator;
+    HRESULT hr = CoCreateInstance(__uuidof(MMDeviceEnumerator), nullptr, CLSCTX_ALL,
+                                  __uuidof(IMMDeviceEnumerator),
+                                  reinterpret_cast<void **>(deviceEnumerator.address()));
+    if (FAILED(hr)) {
+        qWarning() << "Failed to create device enumerator" << hr;
+        return;
+    }
+
+    QComPtr<IMMDevice> device;
+    hr = deviceEnumerator->GetDefaultAudioEndpoint(eRender, eConsole, device.address());
+    if (FAILED(hr)) {
+        qWarning() << "Failed to retrieve default audio endpoint" << hr;
+        return;
+    }
+
+    hr = device->Activate(__uuidof(IAudioClient3), CLSCTX_ALL, nullptr,
+                          reinterpret_cast<void **>(m_warmUpAudioClient.address()));
+    if (FAILED(hr)) {
+        qWarning() << "Failed to activate audio engine" << hr;
+        return;
+    }
+
+    QComTaskResource<WAVEFORMATEX> deviceFormat;
+    UINT32 currentPeriodInFrames = 0;
+    hr = m_warmUpAudioClient->GetCurrentSharedModeEnginePeriod(deviceFormat.address(),
+                                                               &currentPeriodInFrames);
+    if (FAILED(hr)) {
+        qWarning() << "Failed to retrieve the current format and periodicity of the audio engine"
+                   << hr;
+        return;
+    }
+
+    UINT32 defaultPeriodInFrames = 0;
+    UINT32 fundamentalPeriodInFrames = 0;
+    UINT32 minPeriodInFrames = 0;
+    UINT32 maxPeriodInFrames = 0;
+    hr = m_warmUpAudioClient->GetSharedModeEnginePeriod(deviceFormat.get(), &defaultPeriodInFrames,
+                                                        &fundamentalPeriodInFrames,
+                                                        &minPeriodInFrames, &maxPeriodInFrames);
+    if (FAILED(hr)) {
+        qWarning() << "Failed to retrieve the range of periodicities supported by the audio engine"
+                   << hr;
+        return;
+    }
+
+    hr = m_warmUpAudioClient->InitializeSharedAudioStream(
+            AUDCLNT_SHAREMODE_SHARED, minPeriodInFrames, deviceFormat.get(), nullptr);
+    if (FAILED(hr)) {
+        qWarning() << "Failed to initialize audio engine stream" << hr;
+        return;
+    }
+
+    hr = m_warmUpAudioClient->Start();
+    if (FAILED(hr))
+        qWarning() << "Failed to start audio engine" << hr;
+}
+
 QT_END_NAMESPACE
diff --git a/src/multimedia/windows/qwindowsmediadevices_p.h b/src/multimedia/windows/qwindowsmediadevices_p.h
index 4aa1e6577..1973d4769 100644
--- a/src/multimedia/windows/qwindowsmediadevices_p.h
+++ b/src/multimedia/windows/qwindowsmediadevices_p.h
@@ -26,6 +26,7 @@ QT_BEGIN_NAMESPACE
 
 class QWindowsEngine;
 class CMMNotificationClient;
+struct IAudioClient3;
 
 class QWindowsMediaDevices : public QPlatformMediaDevices
 {
@@ -40,11 +41,17 @@ public:
     QPlatformAudioSink *createAudioSink(const QAudioDevice &deviceInfo,
                                         QObject *parent) override;
 
+    void prepareAudio() override;
+
 private:
     QList<QAudioDevice> availableDevices(QAudioDevice::Mode mode) const;
 
     QComPtr<IMMDeviceEnumerator> m_deviceEnumerator;
     QComPtr<CMMNotificationClient> m_notificationClient;
+    // The "warm-up" audio client is required to run in the background in order to keep audio engine
+    // ready for audio output immediately after creating any other subsequent audio client.
+    QComPtr<IAudioClient3> m_warmUpAudioClient;
+    std::atomic_bool m_isAudioClientWarmedUp = false;
 
     friend CMMNotificationClient;
 };