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/****************************************************************************
**
** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** GNU Free Documentation License
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms
** and conditions contained in a signed written agreement between you
** and Nokia.
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page multimediabackend.html
\brief Information for implementing a new multimedia backend.
\ingroup mobility
\tableofcontents
\section1 Multimedia Backend Development
In some cases the available cross-platform Multimedia APIs or implementations are not sufficient,
or not immediately available on a certain platform. In some cases the multimedia
implementation on a platform might expose certain extra properties or functionality
that other platforms do not, or a finer degree of control might be possible. For these
cases, it is possible to use extended controls directly.
In addition, if you plan to port the Qt Multimedia APIs to a new platform, you do
this by implementing certain control and service classes, as detailed below.
\section1 Extending the API
For the developer who wishes to extend the functionality of the Multimedia
classes there are several classes of particular importance. The default
classes are QMediaService, QMediaServiceProvider and QMediaControl.
Basically, the idea is that to use the Multimedia API you would use these
three classes or classes derived from them as follows
\list
\o \l QMediaServiceProvider is used by the top level client class to request a service. The top level class knowing what kind of service it needs.
\o \l QMediaService provides a service and when asked by the top level object, say a component, will return a QMediaControl object.
\o \l QMediaControl allows the control of the service using a known interface.
\endlist
Consider a developer creating, for example, a media player class called MyPlayer.
It may have special requirements beyond ordinary media players and so may
need a custom service and a custom control. We can subclass \l QMediaServiceProvider
to create our MyServiceProvider class. Also we will create a
MyMediaService, and the MyMediaControl to manipulate the media service.
The MyPlayer object calls MyServiceProvider::requestService() to get an
instance of MyMediaService. Then the MyPlayer object calls this service
object it has just received and calling \l {QMediaService::requestControl()}{requestControl()}
it will receive the control object derived from QMediaControl. Now we have
all the parts necessary for our media application. We have the service
provider, the service it provides and the control used to manipulate the
service. Since our MyPlayer object has instances of the service and its
control then it would be possible for these to be used by associated classes
that could do additional actions, perhaps with their own control since the
parameter to requestControl() is a c-type string, \i {const char *}, for the
interface.
\section2 Adding a Media Service Provider
The base class for creating new service providers is \l{QMediaServiceProvider}.
The user must implement the \l{QMediaServiceProvider::requestService()}{requestService()}
function
\code
QMediaService* requestService(const QByteArray &type, const QMediaServiceProviderHint &hint);
\endcode
The details of implementation will depend on the provider. Looking at the
class \l QMediaServiceProvider for the default implementation. Notice that
\l {QMediaServiceProvider::requestService()}{requestService()} uses the
\l QMediaServiceProviderHint to look for the appropriate plugin and then to
insert it into the plugin map. However, for a specific service provider there
is probably no need for this approach, it will simply depend on what the
developer wants to implement.
Other methods that may be overloaded
\code
void releaseService(QMediaService *service);
QtMediaServices::SupportEstimate hasSupport(const QByteArray &serviceType,
const QString &mimeType,
const QStringList& codecs,
int flags) const;
QStringList supportedMimeTypes(const QByteArray &serviceType, int flags) const;
QList<QByteArray> devices(const QByteArray &serviceType) const;
QString deviceDescription(const QByteArray &serviceType, const QByteArray &device);
\endcode
The choice of what needs to be done depends on what the developer wishes to do with the service.
\section2 Classes for service implementers.
\annotatedlist multimedia-serv
*/
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