qtmultimedia/doc/src/multimedia.qdoc

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/*!
    \group multimedia
    \title QtMultimedia
    APIs to play and record sound, play videos, access camera and radio hardware, and manage media playlists.
*/

/*!

\page multimedia.html
\title Multimedia
\brief Provides a set of APIs to play and record sound, play videos, access camera and radio hardware, and manage media playlists.

Multimedia provides a set of APIs that allow the developer to play, record
and manage a collection of media content. It also allows access and control to camera
or analog radio hardware.

\tableofcontents

\section1 Overview

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.

The supplied \l {qtmultimedia examples}{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.

\section2 Audio

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 an audio recorder object. A
\l{QAudioRecorder} object is created. The output file name is then set for the \l{QMediaRecorder} object.

\code
    audioRecorder = new QAudioRecorder;
    audioRecorder->setOutputLocation(QUrl("test.raw"));
\endcode

A list of devices is needed so that an input can be selected in the user interface

\code
    for (int i = 0; i < audioRecorder->deviceCount(); i++)
        deviceBox->addItem(audiosource->name(i));
\endcode

and a list of the supported codecs for the user to select a codec,

\code
    QStringList codecs = audioRecorder->supportedAudioCodecs();
    for (int i = 0; i < codecs.count(); i++)
        codecsBox->addItem(codecs.at(i));
\endcode

To set the selected device or codec just use the index of the device or codec by calling the setter in \i {audiosource} or \i {capture} as appropriate, for example,

\code
    audioRecorder->setSelectedDevice(i);
    ...
    audioRecorder->setAudioCodec(codecIdx);
\endcode

Now start recording by using the \l {QMediaRecorder}{record()} function from the new \l{QMediaRecorder} object

\code
    audioRecorder->record();
\endcode

And stop recording by calling the matching function \l {QMediaRecorder::stop()}{stop()} in \l{QMediaRecorder}.

\code
    audioRecorder->stop();
\endcode

How then would this audio file be played? The \l {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.

\code
    QMediaPlayer *player = new QMediaPlayer;
    ...
    player->setMedia(QUrl::fromLocalFile("test.raw"));
    player->setVolume(50);
    player->play();
\endcode

The filename does not have to be a local file. It could be a URL to a
remote resource. Also by using the \l{QMediaPlaylist} class from this API
we can play a list of local or remote files. The \l{QMediaPlaylist}
class supports constructing, managing and playing playlists.

\code
    player = new QMediaPlayer;

    playlist = new QMediaPlaylist(player);
    playlist->addMedia(QUrl("http://example.com/myfile1.mp3"));
    playlist->addMedia(QUrl("http://example.com/myfile2.mp3"));
    ...
    playlist->setCurrentPosition(1);
    player->play();
\endcode

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.



\section2 Video

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 QtMobility
Project class: \l{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.

\code
    player = new QMediaPlayer;

    playlist = new QMediaPlaylist(player);
    playlist->addMedia(QUrl("http://example.com/myclip1.mp4"));
    playlist->addMedia(QUrl("http://example.com/myclip2.mp4"));
    ...
    widget = new QVideoWidget(player);
    widget->show();

    playlist->setCurrentPosition(1);
    player->play();
\endcode

The \l {player}{Player} example does things a bit differently to our sample
code. Instead of using a QVideoWidget object directly, the Player example
has a \i {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.

\snippet ../../demos/player/player.cpp  2

\omit
\section2 Radio

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.
\endomit


\section1 Camera Support

Creating still images and video.

\section2 Still Images

In order to capture an image we need to create a \l QCamera object and use
it to initialize a \l QVideoWidget, so we can see where the camera is
pointing - a viewfinder. The camera object is also used to initialize a new
QCameraImageCapture object, \i imageCapture. All that is then needed is to start
the camera, lock it so that the settings are not changed while the image
capture occurs, capture the image, and finally unlock the camera ready for
the next photo.

    \code
            camera = new QCamera;
            viewFinder = new QCameraViewfinder();
            viewFinder->show();

            camera->setViewfinder(viewFinder);

            imageCapture = new QCameraImageCapture(camera);

            camera->setCaptureMode(QCamera::CaptureStillImage);
            camera->start();

            //on half pressed shutter button
            camera->searchAndLock();

            ...

            //on shutter button pressed
            imageCapture->capture();

            //on shutter button released
            camera->unlock();
    \endcode

\note Alternatively, we could have used a QGraphicsVideoItem as a viewfinder.


\section2 Video Clips

Previously we saw code that allowed the capture of a still image. Recording
video requires the use of a \l QMediaRecorder object.

To record video we need a camera object, as before, a media recorder and a
viewfinder object. The media recorder object will need to be initialized.

    \code
    camera = new QCamera;
    mediaRecorder = new QMediaRecorder(camera);

    camera->setCaptureMode(QCamera::CaptureVideo);
    camera->start();

    //on shutter button pressed
    mediaRecorder->record();
    \endcode

Signals from the \i mediaRecorder can be connected to slots to react to
changes in the state of the recorder or error events. Recording itself
starts with the \l {QMediaRecorder::record()}{record()} function of
mediaRecorder being called, this causes the signal \l
{QMediaRecorder::stateChanged()}{stateChanged()} to be emitted. The
recording process can be changed with the \l {QMediaRecorder::record()}{record()},
\l {QMediaRecorder::pause()}{pause()}, \l {QMediaRecorder::stop()}{stop()} and
\l {QMediaRecorder::setMuted()}{setMuted()} slots in \l QMediaRecorder.

When the camera is in video mode, as decided by the application, then as the
shutter button is pressed the camera is locked as before but instead the
\l {QMediaRecorder::record()}{record()} function in \l QMediaRecorder is used.



\section2 Focus

Focusing is managed by the classes \l QCameraFocus and \l QCameraFocusControl.
QCameraFocus allows the developer to set the general policy by means of the
enums for the \l {QCameraFocus::FocusMode}{FocusMode} and the
\l {QCameraFocus::FocusPointMode}{FocusPointMode}.
\l {QCameraFocus::FocusMode}{FocusMode} deals with
settings such as \l {QCameraFocus::FocusMode}{AutoFocus},
\l {QCameraFocus::FocusMode}{ContinuousFocus} and
\l {QCameraFocus::FocusMode}{InfinityFocus}, whereas
\l {QCameraFocus::FocusPointMode}{FocusPointMode} deals with the various focus zones within the view.
\l {QCameraFocus::FocusPointMode}{FocusPointMode} has support for face
recognition, center focus and a custom focus where the focus point can be specified.



\section2 Canceling Asynchronous Operations

Various operations such as image capture and auto focusing occur
asynchrously. These operations can often be cancelled by the start of a new
operation as long as this is supported by the backend. For image capture,
the operation can be cancelled by calling
\l {QCameraImageCapture::cancelCapture()}{cancelCapture()}. For \l {QCameraFocus::FocusMode}{auto-focus},
\l {QCameraExposure::ExposureMode}{auto-exposure} or \l {QCameraImageProcessing::WhiteBalanceMode}{white balance}
cancellation can be done by calling \l {QCamera::unlock()}{unlock}(QCamera::LockFocus).


\target qtmultimedia examples
\section1 Examples

\section2 Record a Sound Source

\l{audiorecorder}{AudioRecorder} is a demonstration of the discovery of
the supported devices and codecs and the use of recording functions in the
QMediaRecorder class.

\section2 Play a Media File

The \l{player}{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.

\section2 Slide Show

The \l{slideshow}{Slide Show} shows the use of the QMediaImageViewer and
QVideoWidget classes.

\section2 Camera Example

The \l{Camera Example} shows how use the QtMultimedia API to quickly
write a camera application in C++.

\section2 QML Camera Example

The \l {QML Camera Example} demonstrates still image capture and controls
using the QML plugin. Video recording is not currently available.

\section2 QML Video Example

The \l {video/qmlvideo}{QML Video Example} demonstrates the various manipulations
(move; resize; rotate; change aspect ratio) which can be applied to QML
\l {VideoOutput} items.

It also shows how native code can be combined with QML to implement more
advanced functionality - in this case, C++ code is used to calculate the QML
frame rate.  This value is rendered in QML as a semi-transparent item overlaid
on the video content.

\section2 QML Video Shader Effects Example
The \l {video/qmlvideofx}{QML Video Shader Effects Example} shows how the
\l {ShaderEffect} element can be used to apply postprocessing effects,
expressed in GLSL, to QML \l {VideoOutput} items.

It re-uses the frame rate display code used by the \l {QML Video Example}.

Finally, this application demonstrates the use of different top-level QML
files to handle different physical screen sizes.  On small-screen devices,
menus are by default hidden, and only appear when summoned by a gesture.
Large-screen devices show a more traditional layout in which menus are
displayed around the video content pane.


\section1 Reference documentation

\section2 Core classes

\annotatedlist multimedia_core

\section2 Media playback classes

\annotatedlist multimedia_playback

\section2 Camera classes

\annotatedlist multimedia_camera

\section2 Radio classes

\annotatedlist multimedia_radio

\section2 Media recording classes

\annotatedlist multimedia_recording

\section2 Low level Audio related classes

\annotatedlist multimedia_audio

\section2 Low level Video related classes

\annotatedlist multimedia_video

\section2 QML Elements
\annotatedlist multimedia_qml

See also \l{Multimedia QML Plugin}

\section2 Advanced usage.

For developers wishing to access some platform specific settings, or to
port the Qt Multimedia APIs to a new platform or technology, see \l{Multimedia Backend Development}.

*
***/