QtMultimedia QML Type

Provides a global object with useful functions from Qt Multimedia. 更多...

import 語句：	import QtMultimedia 5.8
Since:	QtMultimedia 5.4

所有成員列錶，包括繼承成員

特性

availableCameras : list<object>
defaultCamera : object

方法

real convertVolume (real volume , VolumeScale from , VolumeScale to )

詳細描述

The QtMultimedia object is a global object with utility functions and properties.

它不可實例化；要使用它，調用成員來自全局 QtMultimedia 對象直接。例如：

Camera {
    deviceId: QtMultimedia.defaultCamera.deviceId
}

特性文檔編製

[read-only] availableCameras : list < object >

This property provides information about the cameras available on the system.

Each object in the list has the following properties:

`deviceId`	This read-only property holds the unique identifier of the camera. You can choose which device to use with a Camera object by setting its deviceId property to this value.
`displayName`	This read-only property holds the human-readable name of the camera. You can use this property to display the name of the camera in a user interface.
`位置`	This read-only property holds the physical position of the camera on the hardware system. Please see Camera.position 瞭解更多信息。
`orientation`	This read-only property holds the physical orientation of the camera sensor. Please see Camera.orientation 瞭解更多信息。

注意： This property is static; it is not updated when cameras are added or removed from the system, like USB cameras on a desktop platform.

The following example shows how to display a list of available cameras. The user can change the active camera by selecting one of the items in the list.

Item {
    Camera {
        id: camera
    }
    VideoOutput {
        anchors.fill: parent
        source: camera
    }
    ListView {
        anchors.fill: parent
        model: QtMultimedia.availableCameras
        delegate: Text {
            text: modelData.displayName
            MouseArea {
                anchors.fill: parent
                onClicked: camera.deviceId = modelData.deviceId
            }
        }
    }
}

[read-only] defaultCamera : object

The defaultCamera object provides information about the default camera on the system.

Its properties are deviceId , displayName , 位置 and orientation 。見 availableCameras for a description of each of them.

If there is no default camera, defaultCamera.deviceId will contain an empty string.

注意： This property is static; it is not updated if the system's default camera changes after the application started.

方法文檔編製

real convertVolume ( real volume , VolumeScale from , VolumeScale to )

轉換音頻 volume from 音量比例縮放 to 另一，並返迴結果。

從屬上下文，錶示音頻音量是使用不同刻度。所有擁有音頻音量的 Qt Multimedia 類都使用綫性刻度，原因是揚聲器響度是通過綫性刻度調製其電壓來控製的。另一方麵，人的耳朵以對數方式感知響度。因此，在大多數應用程序中，音量控製使用對數刻度很閤適。分貝刻度本質上是對數的，且常用於定義聲明級彆，通常用於專業音頻應用程序 UI 音量控製。立方刻度是對數刻度的便宜計算近似，它提供對較低音量級彆的更多控製。

Valid values for from and to 是：

QtMultimedia .LinearVolumeScale - Linear scale. 0.0 (0%) 為無聲而 1.0 (100%) is full volume. All Qt Multimedia types that have an audio volume use a linear scale.
QtMultimedia .CubicVolumeScale - Cubic scale. 0.0 (0%) 為無聲而 1.0 (100%) 為全音量。
QtMultimedia .LogarithmicVolumeScale - Logarithmic scale. 0.0 (0%) 為無聲而 1.0 (100%) 為全音量。通常，UI 音量控製應使用對數比例縮放。
QtMultimedia .DecibelVolumeScale - Decibel (dB, amplitude) logarithmic scale. -200 為無聲而 0 為全音量。

The following example shows how the volume value from a UI volume control can be converted so that the perceived increase in loudness is the same when increasing the volume control from 0.2 to 0.3 as it is from 0.5 to 0.6:

Slider {
    id: volumeSlider
    property real volume: QtMultimedia.convertVolume(volumeSlider.value,
                                                     QtMultimedia.LogarithmicVolumeScale,
                                                     QtMultimedia.LinearVolumeScale)
}
MediaPlayer {
    volume: volumeSlider.volume
}

該 QML 方法在 Qt 5.8 引入。