source: trunk/doc/src/frameworks-technologies/phonon.qdoc@ 651

/****************************************************************************
**
** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation ([email protected])
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial Usage
** Licensees holding valid Qt Commercial licenses may use this file in
** accordance with the Qt Commercial License Agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Nokia.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights.  These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** If you have questions regarding the use of this file, please contact
** Nokia at [email protected].
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \page phonon-overview.html
    \title Phonon Overview
    \ingroup frameworks-technologies

    \tableofcontents

    \section1 Introduction

    Qt uses the Phonon multimedia framework to provide functionality
    for playback of the most common multimedia formats. The media can
    be read from files or streamed over a network, using a QURL to a
    file.

    In this overview, we take a look at the main concepts of Phonon.
    We also explain the architecture, examine the
    core API classes, and show examples on how to use the classes
    provided.

    \section1 Architecture

    Phonon has three basic concepts: media objects, sinks, and paths.
    A media object manages a media source, for instance, a music file;
    it provides simple playback control, such as starting, stopping,
    and pausing the playback. A sink outputs the media from Phonon,
    e.g., by rendering video on a widget, or by sending audio to a
    sound card. Paths are used to connect Phonon objects, i.e., a
    media object and a sink, in a graph - called a media graph in
    Phonon.

    As an example, we show a media graph for an audio stream:

    \image conceptaudio.png

    The playback is started and managed by the media object, which
    send the media stream to any sinks connected to it by a path. The
    sink then plays the stream back, usually though a sound card.

    \omit Not sure if this goes here, or anywhere...
    All nodes in the graph are synchronized by the framework,
    meaning that if more than one sink is connected to the same
    media object, the framework will handle the synchronization
    between the sinks; this happens for instance when a media
    source containing video with sound is played back. More on
    this later.
    \endomit

    \section2 Media Objects

    The media object, an instance of the \l{Phonon::}{MediaObject}
    class, lets you start, pause, and stop the playback of a media
    stream, i.e., it provided basic control over the playback. You may
    think of the object as a simple media player.

    The media data is provided by a media source, which is
    kept by the media object. The media source is a separate
    object - an instance of \l{Phonon::}{MediaSource} - in Phonon, and
    not part of the graph itself. The source will supply the media
    object with raw data. The data can be read from files and streamed
    over a network. The contents of the source will be interpreted by
    the media object.

    A media object is always instantiated with the default constructor
    and then supplied with a media source. Concrete code examples are
    given later in this overview.

    As a complement to the media object, Phonon also provides
    \l{Phonon::}{MediaController}, which provides control over
    features that are optional for a given media. For instance, for
    chapters, menus, and titles of a VOB (DVD) file will be features
    managed by a \l{Phonon::}{MediaController}.

    \section2 Sinks

    A sink is a node that can output media from the graph, i.e., it
    does not send its output to other nodes. A sink is usually a
    rendering device.

    The input of sinks in a Phonon media graph comes from a
    \l{Phonon::}{MediaObject}, though it might have been processed
    through other nodes on the way.

    While the \l{Phonon::}{MediaObject} controls the playback, the
    sink has basic controls for manipulation of the media. With an
    audio sink, for instance, you can control the volume and mute the
    sound, i.e., it represents a virtual audio device. Another example
    is the \l{Phonon::}{VideoWidget}, which can render video on a
    QWidget and alter the brightness, hue, and scaling of the video.

    As an example we give an image of a graph used for playing back a
    video file with sound.

    \image conceptvideo.png

    \section2 Processors

    Phonon does not allow manipulation of media streams directly,
    i.e., one cannot alter a media stream's bytes programmatically
    after they have been given to a media object. We have other nodes
    to help with this: processors, which are placed in the graph on
    the path somewhere between the media object and its sinks. In
    Phonon, processors are of the \l{Phonon::}{Effect} class.

    When inserted into the rendering process, the  processor will
    alter the media stream, and will be active as long as it is part
    of the graph. To stop, it needs to be removed.

    \omit \image conceptprocessor.png \endomit

    The \c {Effect}s may also have controls that affect how the media
    stream is manipulated. A processor applying a depth effect to
    audio, for instance, can have a value controlling the amount of
    depth. An \c Effect can be configured at any point in time.

    \section1 Playback

    In some common cases, it is not necessary to build a graph
    yourself.

    Phonon has convenience functions for building common graphs. For
    playing an audio file, you can use the
    \l{Phonon::}{createPlayer()} function. This will set up the
    necessary graph and return the media object node; the sound can
    then be started by calling its \l{Phonon::MediaObject::}{play()}
    function.

    \snippet snippets/phonon.cpp 0

    We have a similar solution for playing video files, the
    \l{Phonon::}{VideoPlayer}.

    \snippet snippets/phonon.cpp 1

    The VideoPlayer is a widget onto which the video will be drawn. 

    The \c .pro file for a project needs the following line to be added:

    \snippet doc/src/snippets/code/doc_src_phonon.qdoc 0

    Phonon comes with several widgets that provide functionality
    commonly associated with multimedia players - notably SeekSlider
    for controlling the position of the stream, VolumeSlider for
    controlling sound volume, and EffectWidget for controlling the
    parameters of an effect. You can learn about them in the API
    documentation.

    \section1 Building Graphs

    If you need more freedom than the convenience functions described
    in the previous section offers you, you can build the graphs
    yourself. We will now take a look at how some common graphs are
    built. Starting a graph up is a matter of calling the
    \l{Phonon::MediaObject::}{play()} function of the media object.

    If the media source contains several types of media, for instance, a
    stream with both video and audio, the graph will contain two
    output nodes: one for the video and one for the audio. 

    We will now look at the code required to build the graphs discussed
    previously in the \l{Architecture} section. 

    \section2 Audio

    When playing back audio, you create the media object and connect
    it to an audio output node - a node that inherits from
    AbstractAudioOutput. Currently, AudioOutput, which outputs audio
    to the sound card, is provided.

    The code to create the graph is straight forward:

    \snippet snippets/phonon.cpp 2

    Notice that the type of media an input source has is resolved by
    Phonon, so you need not be concerned with this. If a source
    contains multiple media formats, this is also handled
    automatically.

    The media object is always created using the default constructor
    since it handles all multimedia formats.

    The setting of a Category, Phonon::MusicCategory in this case,
    does not affect the actual playback; the category can be used by
    KDE to control the playback through, for instance, the control
    panel.

    \omit Not sure about this
    Users of KDE can often also choose to send sound with the
    CommunicationCategory, e.g., given to VoIP, to their headset,
    while sound with MusicCategory is sent to the sound card.
    \endomit

    The AudioOutput class outputs the audio media to a sound card,
    that is, one of the audio devices of the operating system. An
    audio device can be a sound card or a intermediate technology,
    such as \c DirectShow on windows. A default device will be chosen
    if one is not set with \l{Phonon::AudioOutput::}{setOutputDevice()}.

    The AudioOutput node will work with all audio formats supported by
    the back end, so you don't need to know what format a specific
    media source has.

    For a an extensive example of audio playback, see the \l{Music
    Player Example}{Phonon Music Player}.

    \section3 Audio Effects

    Since a media stream cannot be manipulated directly, the backend
    can produce nodes that can process the media streams. These nodes
    are inserted into the graph between a media object and an output
    node.

    Nodes that process media streams inherit from the Effect class.
    The effects available depends on the underlying system. Most of
    these effects will be supported by Phonon. See the \l{Querying
    Backends for Support} section for information on how to resolve
    the available effects on a particular system.

    We will now continue the example from above using the Path
    variable \c path to add an effect. The code is again trivial:

    \snippet snippets/phonon.cpp 3

    Here we simply take the first available effect on the system.

    The effect will start immediately after being inserted into the
    graph if the media object is playing. To stop it, you have to
    detach it again using \l{Phonon::Path::}{removeEffect()} of the Path.

    \section2 Video

    For playing video, VideoWidget is provided. This class functions
    both as a node in the graph and as a widget upon which it draws
    the video stream. The widget will automatically choose an available
    device for playing the video, which is usually a technology
    between the Qt application and the graphics card, such as \c
    DirectShow on Windows.

    The video widget does not play the audio (if any) in the media
    stream. If you want to play the audio as well, you will need
    an AudioOutput node. You create and connect it to the graph as
    shown in the previous section.

    The code for creating this graph is given below, after which
    one can play the video with \l{Phonon::MediaObject::}{play()}.

    \snippet snippets/phonon.cpp 4

    The VideoWidget does not need to be set to a Category, it is
    automatically classified to \l{Phonon::}{VideoCategory}, we only
    need to assure that the audio is also classified in the same
    category.

    The media object will split files with different media content
    into separate streams before sending them off to other nodes in
    the graph. It is the media object that determines the type of
    content appropriate for nodes that connect to it.

    \omit This section is from the future

    \section2 Multiple Audio Sources and Graph Outputs

    In this section, we take a look at a graph that contains multiple
    audio sources in addition to video. We have a video camera with
    some embarrassing home footage from last weekend's party, a
    microphone with which we intend to add commentary, and an audio
    music file to set the correct mood. It would be an advantage to
    write the graph output to a file for later viewing, but since this
    is not yet supported by Qt backends, we will play it back
    directly.

    <image of party graph>

    <code>

    <code walkthrough>

    \endomit

    \section1 Backends

    The multimedia functionality is not implemented by Phonon itself,
    but by a back end - often also referred to as an engine. This
    includes connecting to, managing, and driving the underlying
    hardware or intermediate technology. For the programmer, this
    implies that the media nodes, e.g., media objects, processors, and
    sinks, are produced by the back end. Also, it is responsible for
    building the graph, i.e., connecting the nodes.

    The backends of Qt use the media systems DirectShow (which
    requires DirectX) on Windows, QuickTime on Mac, and GStreamer on
    Linux. The functionality provided on the different platforms are
    dependent on these underlying systems and may vary somewhat, e.g.,
    in the media formats supported.

    Backends expose information about the underlying system. It can
    tell which media formats are supported, e.g., \c AVI, \c mp3, or
    \c OGG.

    A user can often add support for new formats and filters to the
    underlying system, by, for instance, installing the DivX codex. We
    can therefore not give an exact overview of which formats are
    available with the Qt backends.

    \omit Not sure I want a separate section for this
    \section2 Communication with the Backends

    We cooperate with backends through static functions in the
    Phonon namespace. We have already seen some of these functions
    in code examples. Their two main responsibilities are creating
    graph nodes and supplying information about the capabilities
    of the various nodes. The nodes uses the backend internally
    when created, so it is only connecting them in the graph that
    you need to use the backend directly.

    The main functions for graph building are:

    \list
        \o createPath(): This function creates a path between to
                         nodes, which it takes as arguments.
        \o 
    \endlist

    For more detailed information, please consult the API
    documentation.

    \endomit

    \section2 Querying Backends for Support

    As mentioned, Phonon depends on the backend to provide its
    functionality. Depending on the individual backend, full support
    of the API may not be in place. Applications therefore need to
    check with the backend if functionality they require is
    implemented. In this section, we take look at how this is done.

    The backend provides the
    \l{Phonon::BackendCapabilities::}{availableMimeTypes()} and
    \l{Phonon::BackendCapabilities::}{isMimeTypeAvailable()} functions
    to query which MIME types the backend can produce nodes for. The
    types are listed as strings, which for any type is equal for any
    backend or platform.

    The backend will emit a signal -
    \l{Phonon::BackendCapabilities::}{Notifier::capabilitiesChanged()}
    - if its abilities have changed. If the available audio devices
    have changed, the
    \l{Phonon::BackendCapabilities::}{Notifier::availableAudioOutputDevicesChanged()}
    signal is emitted instead.

    To query the actual audio devices possible, we have the
    \l{Phonon::BackendCapabilities::}{availableAudioOutputDevices()} as
    mentioned in the \l{#Sinks}{Sinks} section. To query information
    about the individual devices, you can examine its \c name(); this
    string is dependent on the operating system, and the Qt backends
    does not analyze the devices further.

    The sink for playback of video does not have a selection of
    devices. For convenience, the \l{Phonon::}{VideoWidget} is both a
    node in the graph and a widget on which the video output is
    rendered. To query the various video formats available, use
    \l{Phonon::BackendCapabilities::}{isMimeTypeAvailable()}.  To add
    it to a path, you can use the Phonon::createPath() as usual. After
    creating a media object, it is also possible to call its
    \l{Phonon::MediaObject::}{hasVideo()} function.

    See also the \l{Capabilities Example}.

    \section1 Installing Phonon

    When running the Qt configure script, you will be notified whether
    Phonon support is available on your system. As mentioned
    previously, to use develop and run Phonon applications, you also
    need to link to a backend, which provides the multimedia
    functionality.

    Note that Phonon applications will compile and run without a
    working backend, but will, of course, not work as expected.

    The following sections explains requirements for each backend.

    \section2 Windows

    On Windows, building Phonon requires DirectX and DirectShow
    version 9 or higher. You'll need additional SDKs you can download
    from Microsoft.

    \section3 Windows XP and later Windows versions

    If you develop for Windows XP and up, you should download the Windows SDK
    \l{http://www.microsoft.com/downloads/details.aspx?FamilyID=e6e1c3df-a74f-4207-8586-711ebe331cdc&amp;DisplayLang=en}{here}.
    Before building Qt, just call the script: \c {C:\Program Files\Microsoft SDKs\Windows\v6.1\Bin\setenv.cmd}

    \note Visual C++ 2008 already contains the Windows SDK and doesn't
    need that package and has already the environment set up for a
    smooth compilation of phonon.

    \section3 Earlier Windows versions than Windows XP

    If you want to support previous Windows versions, you should download and install the Platform SDK. You find it
    \l{http://www.microsoft.com/downloads/details.aspx?FamilyId=0BAF2B35-C656-4969-ACE8-E4C0C0716ADB&amp;displaylang=en}{here}.

    \note The platform SDK provided with Visual C++ is not
    complete and
    you'll need this one to have DirectShow 9.0 support. You can download the DirectX SDK
    \l{http://www.microsoft.com/downloads/details.aspx?familyid=09F7578C-24AA-4E0A-BF91-5FEC24C8C7BF&amp;displaylang=en}{here}.

    \section3 Setting up the environment

    Once the SDKs are installed, please make sure to set your
    environment variables LIB and INCLUDE correctly. The paths to the
    include and lib directory of the SDKs should appear first.
    Typically, to setup your environment, you would execute the
    following script:

    \code
        Set DXSDK_DIR=C:\Program Files\Microsoft DirectX SDK (February 2007)
        %DXSDK_DIR%\utilities\bin\dx_setenv.cmd
        C:\program files\Microsoft Platform SDK\setenv.cmd
    \endcode

    If your environment is setup correctly, executing configure.exe on
    your Qt installation should automatically activate Phonon.

    \warning The MinGW version of Qt does not support building the
             Qt backend.

    \section2 Linux

    The Qt backend on Linux uses GStreamer (minimum version is 0.10),
    which must be installed on the system. At a minimum, you need the
    GStreamer library and base plugins, which provides support for \c
    .ogg files. The package names may vary between Linux
    distributions; on Mandriva, they have the following names:

    \table
        \header
            \o Package
            \o Description
        \row
            \o libgstreamer0.10_0.10
            \o The GStreamer base library.
        \row
            \o libgstreamer0.10_0.10-devel
            \o Contains files for developing applications with
               GStreamer.
        \row
            \o libgstreamer-plugins-base0.10
            \o Contains the basic plugins for audio and video
               playback, and will enable support for \c ogg files.
        \row
            \o libgstreamer-plugins-base0.10-devel
            \o Makes it possible to develop applications using the
               base plugins.
    \endtable

    \omit Should go in troubleshooting (in for example README)
    alsasink backend for GStreamer
    \table
        \header
            \o Variable
            \o Description
        \row
            \o PHONON_GST_AUDIOSINK
            \o Sets the audio sink to be used. Possible values are
               ... alsasink.
        \row
            \o PHONON_GSTREAMER_DRIVER
            \o Sets the driver for GStreamer. This driver will
               usually be configured automatically when
               installing.
        \row
            \o PHONON_GST_VIDEOWIDGET
            \o This variable can be set to the name of a widget to
               use as the video widget??
        \row
            \o PHONON_GST_DEBUG
            \o Phonon will give debug information while running if
               this variable is set to a number between 1 and 3.
        \row
            \o PHONON_TESTURL
            \o ...
    \endtable
    \endomit

    \section2 Mac OS X

    On Mac OS X, Qt uses QuickTime for its backend. The minimum
    supported version is 7.0.

    \section1 Deploying Phonon Applications on Windows and Mac OS X

    On Windows and Mac OS X, the Qt backend makes use of the
    \l{QtOpenGL Module}{QtOpenGL} module. You therefore need to deploy
    the QtOpenGL shared library. If this is not what you want, it is
    possible to configure Qt without OpenGL support. In that case, you
    need to run \c configure with the \c -no-opengl option.

    \section1 Work in Progress

    Phonon and its Qt backends, though fully functional for
    multimedia playback, are still under development. Functionality to
    come is the possibility to capture media and more processors for
    both music and video files.

    Another important consideration is to implement support for
    storing media to files; i.e., not playing back media directly.

    We also hope in the future to be able to support direct
    manipulation of media streams. This will give the programmer more
    freedom to manipulate streams than just through processors.

    Currently, the multimedia framework supports one input source. It will be
    possible to include several sources. This is useful in, for example, audio
    mixer applications where several audio sources can be sent, processed and
    output as a single audio stream.
*/