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Multimedia provides a set of APIs that allow the developer to play, record and manage a collection of media content. It is dependent on the QtMultimediaKit module. This API is planned to replace Phonon at a later stage.
Unlike the other APIs in Qt Mobility, the Multimedia API is not in the QtMobility namespace.
This library will require Qt 4.6.
This API delivers an easy to use interface to multimedia functions. The developer can use the API to display an image, or a video, record sound or play a multimedia stream.
There are several benefits this API brings to Qt. Firstly, the developer can now implement fundamental multimedia functions with minimal code, mostly because they are already implemented. Also there is a great deal of flexibility with the media source or the generated multimedia. The source file does not need to be local to the device, it could be streamed from a remote location and identified by a URL. Finally, many different codecs are supported 'out of the box'.
The supplied examples give a good idea at the ease of use of the API. When the supporting user interface code is ignored we can see that functionality is immediately available with minimal effort.
The Audio Recorder example is a good introduction to the basic use of the API. We will use snippets from this example to illustrate how to use the API to quickly build functionality.
The first step is to demonstrate recording audio to a file. When recording from an audio source there are a number of things we may want to control beyond the essential user interface. We may want a particular encoding of the file, MP3 or Ogg Vorbis for instance, or select a different input source. The user may modify the bitrate, number of channels, quality and sample rate. Here the example will only modify the codec and the source device, since they are essential.
To begin, the developer sets up a source and a recorder object. A QAudioCaptureSource object is created and used to initialize a QMediaRecorder object. The output file name is then set for the QMediaRecorder object.
audiosource = new QAudioCaptureSource; capture = new QMediaRecorder(audiosource); capture->setOutputLocation(QUrl("test.raw"));
A list of devices is needed so that an input can be selected in the user interface
for(int i = 0; i < audiosource->deviceCount(); i++) deviceBox->addItem(audiosource->name(i));
and a list of the supported codecs for the user to select a codec,
QStringList codecs = capture->supportedAudioCodecs(); for(int i = 0; i < codecs.count(); i++) codecsBox->addItem(codecs.at(i));
To set the selected device or codec just use the index of the device or codec by calling the setter in audiosource or capture as appropriate, for example,
audiosource->setSelectedDevice(i); ... capture->setAudioCodec(codecIdx);
Now start recording by using the record() function from the new QMediaRecorder object
capture->record();
And stop recording by calling the matching function stop() in QMediaRecorder.
capture->stop();
How then would this audio file be played? The QMediaPlayer class will be used as a generic player. Since the player can play both video and audio files the interface will be more complex, but for now the example will concentrate on the audio aspect.
Playing the file is simple: create a player object, pass in the filename, set the volume or other parameters, then play. Not forgetting that the code will need to be hooked up to the user interface.
QMediaPlayer *player = new QMediaPlayer; ... player->setMedia(QUrl::fromLocalFile("test.raw")); player->setVolume(50); player->play();
The filename does not have to be a local file. It could be a URL to a remote resource. Also by using the QMediaPlaylist class from this API we can play a list of local or remote files. The QMediaPlaylist class supports constructing, managing and playing playlists.
player = new QMediaPlayer; playlist = new QMediaPlaylist(player); playlist->append(QUrl("http://example.com/myfile1.mp3")); playlist->append(QUrl("http://example.com/myfile2.mp3")); ... playlist->setCurrentPosition(1); player->play();
To manipulate the playlist there are the usual management functions (which are in fact slots): previous, next, setCurrentPosition and shuffle. Playlists can be built, saved and loaded using the API.
Continuing with the example discussed for an Audio recorder/player, we can use this to show how to play video files with little change to the code.
Moving from audio to video requires few changes in the sample code. To play a video playlist the code can be changed to include another new Mobility Project class: QVideoWidget. This class enables control of a video resource with signals and slots for the control of brightness, contrast, hue, saturation and full screen mode.
player = new QMediaPlayer; playlist = new QMediaPlaylist(player); playlist->append(QUrl("http://example.com/myclip1.mp4")); playlist->append(QUrl("http://example.com/myclip2.mp4")); ... widget = new QVideoWidget(player); widget->show(); playlist->setCurrentPosition(1); player->play();
The Player example does things a bit differently to our sample code. instead of using a QVideoWidget object directly, the Player example has a VideoWidget class that inherits from QVideoWidget. This means that functions can be added to provide functions such as full screen display, either on a double click or on a particular keypress.
videoWidget = new VideoWidget(this); player->setVideoOutput(videoWidget); playlistModel = new PlaylistModel(this); playlistModel->setPlaylist(playlist);
QRadioTunerControl is a pure virtual base class that will be the basis for any platform specific radio device control. When the functions are implemented the developer will be able to quickly produce an application that supports the typical uses of an FM radio including tuning, volume, start, stop and various other controls.
The base class for creating new service providers is QMediaServiceProvider. The user must implement the requestService() function
QMediaService* requestService(const QByteArray &type, const QMediaServiceProviderHint &hint);
The details of implementation will depend on the provider. Looking at the class QMediaServiceProvider for the default implementation. Notice that requestService() uses the 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
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);
The choice of what needs to be done depends on what the developer wishes to do with the service.
AudioRecorder is a demonstration of the discovery of the supported devices and codecs and the use of recording functions in the QMediaRecorder class.
The Player example is a simple multimedia player. Select a video file to play, stop, pause, show in fullscreen or manipulate various image attributes using the Color Options button.
The Slide Show shows the use of the QMediaImageViewer and QVideoWidget classes.
QAudio | Contains enums used by the audio classes |
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QAudioCaptureSource | Interface to query and select an audio input endpoint |
QAudioDeviceInfo | Interface to query audio devices and their functionality |
QAudioEncoderControl | Access to the settings of a media service that performs audio encoding |
QAudioEncoderSettings | Set of audio encoder settings |
QAudioEndpointSelector | Audio endpoint selector media control |
QAudioFormat | Stores audio parameter information |
QAudioInput | Interface for receiving audio data from an audio input device |
QAudioOutput | Interface for sending audio data to an audio output device |
QGraphicsVideoItem | Graphics item which display video produced by a QMediaObject |
QImageEncoderControl | Access to the settings of a media service that performs image encoding |
QMediaBindableInterface | The base class for objects extending media objects functionality |
QMediaContainerControl | Access to the output container format of a QMediaService |
QMediaContent | Access to the resources relating to a media content |
QMediaControl | Base interface for media service controls |
QMediaImageViewer | Means of viewing image media |
QMediaObject | Common base for multimedia objects |
QMediaPlayer | Allows the playing of a media source |
QMediaPlayerControl | Access to the media playing functionality of a QMediaService |
QMediaPlaylist | List of media content to play |
QMediaPlaylistControl | Access to the playlist functionality of a QMediaService |
QMediaPlaylistSourceControl | Access to the playlist playback functionality of a QMediaService |
QMediaRecorder | Used for the recording of media content |
QMediaRecorderControl | Access to the recording functionality of a QMediaService |
QMediaResource | Description of a media resource |
QMediaService | Common base class for media service implementations |
QMediaServiceProviderHint | Describes what is required of a QMediaService |
QMediaStreamsControl | Media stream selection control |
QMediaTimeInterval | Represents a time interval with integer precision |
QMediaTimeRange | Represents a set of zero or more disjoint time intervals |
QMetaDataWriterControl | Write access to the meta-data of a QMediaService's media |
QRadioTuner | Interface to the systems analog radio device |
QRadioTunerControl | Access to the radio tuning functionality of a QMediaService |
QVideoDeviceControl | Video device selector media control |
QVideoEncoderControl | Access to the settings of a media service that performs video encoding |
QVideoRendererControl | Control for rendering to a video surface |
QVideoWidget | Widget which presents video produced by a media object |
QVideoWidgetControl | Media control which implements a video widget |
QVideoWindowControl | Media control for rendering video to a window |
QtMultimediaKit | Contains miscellaneous identifiers used throughout the Qt Media services library |
QMetaDataReaderControl | Read access to the meta-data of a QMediaService's media |
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Copyright © 2010 Nokia Corporation and/or its subsidiary(-ies) | Trademarks | Qt Mobility Project 1.0.2 |