Improve QAudioDeviceInfo::defaultDevice().

The previous implementation of QAudioDeviceInfo::defaultXDevice() would
always report the first available device as the "default" one, making
the order, in which devices were listed, a hidden requirement when
implementing audio plugins. To make it easier and more reliable to
retrieve the default device, all new plugins should implement the new
QAudioSystemPluginExtension interface as well as the QAudioSystemPlugin.

Devices will be chosen in the following order (first match wins):
default plugin -> default device
               -> first available device
plugins -> default device
        -> first available device

Task-number: QTBUG-51292
Change-Id: I8ace78858976fe7c60a2c4a117ef15c4e1bb177f
Reviewed-by: Yoann Lopes <yoann.lopes@qt.io>

1 files changed, 71 insertions, 0 deletions

diff --git a/src/multimedia/audio/qaudiosystempluginext_p.h b/src/multimedia/audio/qaudiosystempluginext_p.h
new file mode 100644
index 000000000..380bc5afa
--- /dev/null
+++ b/src/multimedia/audio/qaudiosystempluginext_p.h
@@ -0,0 +1,71 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
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+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QAUDIOSYSTEMPLUGINEXT_P_H
+#define QAUDIOSYSTEMPLUGINEXT_P_H
+
+#include <QtMultimedia/qtmultimediadefs.h>
+#include <QtMultimedia/qaudio.h>
+#include <QtCore/qplugin.h>
+
+QT_BEGIN_NAMESPACE
+
+//
+//  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.
+//
+
+struct Q_MULTIMEDIA_EXPORT QAudioSystemPluginExtension
+{
+    virtual QByteArray defaultDevice(QAudio::Mode) const = 0;
+    virtual ~QAudioSystemPluginExtension();
+};
+
+#define QAudioSystemPluginExtension_iid "org.qt-project.qt.audiosystempluginextension"
+Q_DECLARE_INTERFACE(QAudioSystemPluginExtension, QAudioSystemPluginExtension_iid)
+
+QT_END_NAMESPACE
+
+#endif // QAUDIOSYSTEMPLUGINEXT_P_H