Qt Multimedia QML API

Overview

The Qt Multimedia module gives developers a simplified way to use audio and video playback, and access camera functionality. The Multimedia QML API provides a QML friendly interface to these features.

Types

Audio

Audio is an easy way to add audio playback to a Qt Quick scene. Qt Multimedia provides properties for control, methods (functions) and signals.

The code extract below shows the creation and use of an Audio instance.

Item {
    width: 640
    height: 360

    Audio {
        id: playMusic
        source: "music.wav"
    }

    MouseArea {
        id: playArea
        anchors.fill: parent
        onPressed:  { playMusic.play() }
    }
}

The snippet above shows how the inclusion of playMusic enables audio features on the type that contains it. So that when the parent's MouseArea is clicked the play() method of Audio is run. Other typical audio control methods are available such as pause() and stop().

Much of the getting / setting of Audio parameters is done through properties. These include

Property Description
source The source URL of the media.
autoLoad Indicates if loading of media should begin immediately.
playing Indicates that the media is playing.
paused The media is paused.
status The status of media loading.
duration Amount of time in milliseconds the media will play.
position Current position in the media in milliseconds of play.
volume Audio output volume: from 0.0 (silent) to 1.0 (maximum)
muted Indicates audio is muted.
bufferProgress Indicates how full the data buffer is: 0.0 (empty) to 1.0 (full).
seekable Indicates whether the audio position can be changed.
playbackRate The rate at which audio is played at as a multiple of the normal rate.
error An error code for the error state including NoError
errorString A description of the current error condition.

The set of signals available allow the developer to create custom behavior when the following events occur,

Signal Description
playing Called when playback is started, or when resumed from paused state.
paused Called when playback is paused.
stopped Called when playback is stopped.
error Called when the specified error occurs.

Camera

Camera enables still image and video capture using QML. It has a number of properties that help setting it up.

The details of using a Camera are described in further depth in the Camera Overview and in the corresponding reference documentation.

Video

Adding video playback, with sound, to a Qt Quick scene is also easy. The process is very similar to that of Audio above, in fact Video shares many of the property names, methods and signals. Here is the equivalent sample code to implement video playback in a scene

Video {
    id: video
    width : 800
    height : 600
    source: "video.avi"

    MouseArea {
        anchors.fill: parent
        onClicked: {
            video.play()
        }
    }

    focus: true
    Keys.onSpacePressed: video.paused = !video.paused
    Keys.onLeftPressed: video.position -= 5000
    Keys.onRightPressed: video.position += 5000
}

There are similar features like play() with new features specific to video.

In the above sample when the parent of MouseArea is clicked, an area of 800x600 pixels with an id of 'video', the source "video.avi" will play in that area. Notice also that signals for the Keys have been defined so that a spacebar will toggle the pause button; the left arrow will move the current position in the video to 5 seconds previously; and the right arrow will advance the current position in the video by 5 seconds.

Most of the differences will obviously be about video control and information. There are many properties associated with Video, most of them deal with meta-data, control of the video media and aspects of presentation.

SoundEffect

SoundEffect provides a way to play short sound effects, like in video games. Multiple sound effect instances can be played simultaneously. You should use Audio for music playback.

Item {
    width: 640
    height: 360

    SoundEffect {
        id: effect
        source: "test.wav"
    }
    MouseArea {
        id: playArea
        anchors.fill: parent
        onPressed:  { effect.play() }
    }
}

In the above sample the sound effect will be played when the MouseArea is clicked.

For a complete description of this type, see SoundEffect

Multimedia QML Types

Video

A convenience type for showing a specified video

Audio

Add audio playback to a scene

MediaPlayer

Add media playback to a scene

Camera

Access viewfinder frames, and take photos and movies

CameraCapture

An interface for capturing camera images

CameraExposure

An interface for exposure related camera settings

CameraFlash

An interface for flash related camera settings

CameraFocus

An interface for focus related camera settings

CameraImageProcessing

An interface for camera capture related settings

CameraRecorder

Controls video recording with the Camera

QtMultimedia

Provides a global object with useful functions from Qt Multimedia

Playlist

For specifying a list of media to be played

PlaylistItem

Defines an item in a Playlist

Radio

Access radio functionality from a QML application

RadioData

Access RDS data from a QML application

Torch

Simple control over torch functionality

SoundEffect

Type provides a way to play sound effects in QML

VideoOutput

Render video or camera viewfinder

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