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Details

Type: Bug
Resolution: Done
Priority: P2: Important
Fix Version/s: 6.3.0 Alpha, 6.2
Affects Version/s: 6.2.0
Component/s: Multimedia
Labels:
None
Environment:
Android 11.0

Platform/s:

Android
Commits:
d805e2c245e1722e350fcfebabec42fbddd0b22b (qt/qtmultimedia/dev) 2b741a5561bae8eee984891ec0728c80d95b9cb1 (qt/qtmultimedia/6.2)
Sprint:
2021wk44POAndroid&Mobile

Description

Not sure if this should work at all, but the workaround I have is ugly.

Example showing the problem:

import QtQuick
import QtQuick.Window
import QtMultimedia
import QtQuick.Controls

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Example fails first")
    Component{
        id: startPage
        Button{
            text: "Open camera"
            onClicked: stackView.push( cameraPage )
        }
    }
    Component{
        id: cameraPage
        Item{
            VideoOutput{
                id: viewFinder
                anchors.fill: parent
            }
            CaptureSession{
                id: captureSession
                camera: Camera{}
                videoOutput: viewFinder
            }
            Button{
                text: "Back"
                anchors.left: parent.left
                anchors.bottom: parent.bottom
                onClicked: {
                    captureSession.camera.stop();
                    stackView.pop();
                }
            }
            Component.onCompleted: captureSession.camera.start();
        }
    }
    StackView{
        id: stackView
        initialItem: startPage
        anchors.fill: parent
    }
}

Open app in android
Press "Open camera"
Grant camera permission
The camera preview does not show in the VideoOutput
Press "Back"
Press "Open camera"
The camera preview does show in the VideoOutput

Ugly workaround:

import QtQuick
import QtQuick.Window
import QtMultimedia
import QtQuick.Controls

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Example ugly workaround")
    Component{
        id: startPage
        Button{
            text: "Open camera"
            onClicked: stackView.push( cameraPage )
        }
    }
    Component{
        id: cameraPage
        Item{
            VideoOutput{
                id: viewFinder
                anchors.fill: parent
            }
            CaptureSession{
                id: captureSession
                camera: Camera{}
                videoOutput: viewFinder
            }
            Connections{
                target: captureSession.camera
                function onActiveChanged(){
                    if( captureSession.camera.active )
                        cameraStarter.running = false;
                }
            }
            Button{
                text: "Back"
                anchors.left: parent.left
                anchors.bottom: parent.bottom
                onClicked: {
                    captureSession.camera.stop();
                    stackView.pop();
                }
            }
            Timer{
                id: cameraStarter
                running: true
                interval: 250
                repeat: true
                onTriggered: captureSession.camera.start()
            }
        }
    }
    StackView{
        id: stackView
        initialItem: startPage
        anchors.fill: parent
    }
}

In this basic example without StackView it just works:

import QtQuick
import QtQuick.Window
import QtMultimedia
import QtQuick.Controls

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Example works")
    VideoOutput{
        id: viewFinder
        anchors.fill: parent
    }
    CaptureSession{
        id: captureSession
        camera: Camera{}
        videoOutput: viewFinder
    }
    Component.onCompleted: captureSession.camera.start();
}

Maybe related to https://bugreports.qt.io/browse/QTBUG-96346 ?