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>

4 files changed, 11 insertions, 3 deletions

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;