Qt Multimedia QML API

概述

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.

類型

音頻

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

特性	描述
source	媒體的源 URL。
autoLoad	Indicates if loading of media should begin immediately.
playing	Indicates that the media is playing.
paused	媒體已暫停。
status	媒體加載的狀態。
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,

信號	描述
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 攝像頭概述 and in the corresponding reference documentation.

視頻

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 被點擊。

此類型的完整描述，見 SoundEffect

Multimedia QML 類型

Audio	把音頻迴放添加到場景
Camera	訪問取景器幀，並拍攝照片及影片
CameraCapture	捕獲攝像頭圖像的接口
CameraExposure	曝光相關攝像頭設置的接口
CameraFlash	閃光相關攝像頭設置的接口
CameraFocus	對焦相關攝像頭設置的接口
CameraImageProcessing	攝像頭捕獲相關設置的接口
CameraRecorder	控製攝像頭錄製視頻
MediaPlayer	把媒體迴放添加到場景
Playlist	針對要播放的指定媒體列錶
PlaylistItem	定義 Playlist 項
QtMultimedia	提供具有 Qt Multimedia 有用功能的全局對象
RadioData	從 QML 應用程序訪問 RDS 數據
SoundEffect	提供在 QML 中播放音效方式的類型
Torch	簡單控製手電筒功能
Video	展示指定視頻的方便類型
VideoOutput	渲染視頻或攝像頭取景器