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diff --git a/doc/src/examples/musicplayerexample.qdoc b/doc/src/examples/musicplayerexample.qdoc new file mode 100644 index 0000000..d23c1f1 --- /dev/null +++ b/doc/src/examples/musicplayerexample.qdoc @@ -0,0 +1,248 @@ +/**************************************************************************** +** +** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). +** Contact: Qt Software Information (qt-info@nokia.com) +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:LGPL$ +** No Commercial Usage +** This file contains pre-release code and may not be distributed. +** You may use this file in accordance with the terms and conditions +** contained in the either Technology Preview License Agreement or the +** Beta Release License Agreement. +** +** 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 1.0, 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 are unsure which license is appropriate for your use, please +** contact the sales department at qt-sales@nokia.com. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \example phonon/musicplayer + \title Music Player Example + + The Music Player Example shows how to use Phonon - the multimedia + framework that comes with Qt - to create a simple music player. + The player can play music files, and provides simple playback + control, such as pausing, stopping, and resuming the music. + + \image musicplayer.png + + The player has a button group with the play, pause, and stop + buttons familiar from most music players. The top-most slider + controls the position in the media stream, and the bottom slider + allows adjusting the sound volume. + + The user can use a file dialog to add music files to a table, + which displays meta information about the music - such as the + title, album, and artist. Each row contains information about a + single music file; to play it, the user selects that row and + presses the play button. Also, when a row is selected, the files + in the table are queued for playback. + + Phonon offers playback of sound using an available audio device, + e.g., a sound card or an USB headset. For the implementation, we + use two objects: a \l{Phonon::}{MediaObject}, which controls the + playback, and an \l{Phonon::}{AudioOutput}, which can output the + audio to a sound device. We will explain how they cooperate when + we encounter them in the code. For a high-level introduction to + Phonon, see its \l{Phonon Overview}{overview}. + + The API of Phonon is implemented through an intermediate + technology on each supported platform: DirectShow, QuickTime, and + GStreamer. The sound formats supported may therefore vary from + system to system. We do not in this example try to determine which + formats are supported, but let Phonon report an error if the user + tries to play an unsupported sound file. + + Our player consists of one class, \c MainWindow, which both + constructs the GUI and handles the playback. We will now go + through the parts of its definition and implementation that + concerns Phonon. + + \section1 MainWindow Class Definition + + Most of the API in \c MainWindow is private, as is often the case + for classes that represent self-contained windows. We list Phonon + objects and slots we connect to their signals; we take a closer + look at them when we walk through the \c MainWindow + implementation. + + \snippet examples/phonon/musicplayer/mainwindow.h 2 + + We use the \l{Phonon::}{SeekSlider} to move the current playback + position in the media stream, and the \l{Phonon::}{VolumeSlider} + controls the sound volume. Both of these widgets come ready made + with Phonon. We use another \l{Phonon::}{MediaObject}, + metaInformationProvider, to get the meta information from the + music files. More on this later. + + \snippet examples/phonon/musicplayer/mainwindow.h 1 + + The \l{Phonon::}{MediaObject} informs us of the state of the playback and + properties of the media it is playing back through a series of + signals. We connect the signals we need to slots in \c MainWindow. + The \c tableClicked() slot is connected to the table, so that we + know when the user requests playback of a new music file, by + clicking on the table. + + \section1 MainWindow Class Implementation + + The \c MainWindow class handles both the user interface and + Phonon. We will now take a look at the code relevant for Phonon. + The code required for setting up the GUI is explained elsewhere. + + We start with the constructor: + + \snippet examples/phonon/musicplayer/mainwindow.cpp 0 + + We start by instantiating our media and audio output objects. + As mentioned, the media object knows how to playback + multimedia (in our case sound files) while the audio output + can send it to a sound device. + + For the playback to work, the media and audio output objects need + to get in contact with each other, so that the media object can + send the sound to the audio output. Phonon is a graph based + framework, i.e., its objects are nodes that can be connected by + paths. Objects are connected using the \c createPath() function, + which is part of the Phonon namespace. + + \snippet examples/phonon/musicplayer/mainwindow.cpp 1 + + We also connect signals of the media object to slots in our \c + MainWindow. We will examine them shortly. + + \snippet examples/phonon/musicplayer/mainwindow.cpp 2 + + Finally, we call private helper functions to set up the GUI. + The \c setupUi() function contains code for setting up the seek + , and volume slider. We move on to \c setupUi(): + + \snippet examples/phonon/musicplayer/mainwindow.cpp 3 + \dots + \snippet examples/phonon/musicplayer/mainwindow.cpp 4 + + After creating the widgets, they must be supplied with the + \l{Phonon::}{MediaObject} and \l{Phonon::}{AudioOutput} objects + they should control. + + In the \c setupActions(), we connect the actions for the play, + pause, and stop tool buttons, to slots of the media object. + + \snippet examples/phonon/musicplayer/mainwindow.cpp 5 + + We move on to the the slots of \c MainWindow, starting with \c + addFiles(): + + \snippet examples/phonon/musicplayer/mainwindow.cpp 6 + + In the \c addFiles() slot, we add files selected by the user to + the \c sources list. We then set the first source selected on the + \c metaInformationProvider \l{Phonon::}{MediaObject}, which will + send a state changed signal when the meta information is resolved; + we have this signal connected to the \c metaStateChanged() slot. + + The media object informs us of state changes by sending the \c + stateChanged() signal. The \c stateChanged() slot is connected + to this signal. + + \snippet examples/phonon/musicplayer/mainwindow.cpp 9 + + The \l{Phonon::MediaObject::}{errorString()} function gives a + description of the error that is suitable for users of a Phonon + application. The two values of the \l{Phonon::}{ErrorState} enum + helps us determine whether it is possible to try to play the same + file again. + + \snippet examples/phonon/musicplayer/mainwindow.cpp 10 + + We update the GUI when the playback state changes, i.e., when it + starts, pauses, stops, or resumes. + + The media object will report other state changes, as defined by the + \l{Phonon::}{State} enum. + + The \c tick() slot is connected to a \l{Phonon::}{MediaObject} signal which is + emitted when the playback position changes: + + \snippet examples/phonon/musicplayer/mainwindow.cpp 11 + + The \c time is given in milliseconds. + + When the table is clicked on with the mouse, \c tableClick() + is invoked: + + \snippet examples/phonon/musicplayer/mainwindow.cpp 12 + + Since we stop the media object, we first check whether it is + currently playing. \c row contains the row in the table that was + clicked upon; the indices of \c sources follows the table, so we + can simply use \c row to find the new source. + + \snippet examples/phonon/musicplayer/mainwindow.cpp 13 + + When the media source changes, we simply need to select the + corresponding row in the table. + + \snippet examples/phonon/musicplayer/mainwindow.cpp 14 + + When \c metaStateChanged() is invoked, \c + metaInformationProvider has resolved the meta data for its current + source. A \l{Phonon::}{MediaObject} will do this before + entering \l{Phonon::}{StoppedState}. Note that we could also + have used the \l{Phonon::MediaObject::}{metaDataChanged()} signal for + this purpose. + + Some of the meta data is then chosen to be displayed in the + music table. A file might not contain the meta data requested, + in which case an empty string is returned. + + \snippet examples/phonon/musicplayer/mainwindow.cpp 15 + + If we have media sources in \c sources of which meta information + is not resolved, we set a new source on the \c + metaInformationProvider, which will invoke \c metaStateChanged() + again. + + We move on to the \c aboutToFinish() slot: + + \snippet examples/phonon/musicplayer/mainwindow.cpp 16 + + When a file is finished playing, the Music Player will move on and + play the next file in the table. This slot is connected to the + \l{Phonon::}{MediaObject}'s + \l{Phonon::MediaObject::}{aboutToFinish()} signal, which is + guaranteed to be emitted while there is still time to enqueue + another file for playback. + + \section1 The main() function. + + Phonon requires that the application has a name; it is set with + \l{QCoreApplication::}{setApplicationName()}. This is because + D-Bus, which is used by Phonon on Linux systems, demands this. + + \snippet examples/phonon/musicplayer/main.cpp 1 +*/ |