Can't load Camera in Debian virtual machine

diego-qt

Hello,
I've been trying for some days to use my webcam in a QtQuick app in a Debian virtual machine but I haven't been successful. The simplified version of my code is this :

import QtQuick 2.15
import QtQuick.Window 2.15
import QtMultimedia 5.15

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    property bool isCameraAvailable: QtMultimedia.availableCameras.length > 0

    Camera {
        id: camera
        deviceId: isCameraAvailable ? QtMultimedia.availableCameras[0].deviceId : ""
        captureMode: Camera.CaptureViewfinder
    }

    VideoOutput {
        id: viewfinder
        anchors.fill: parent
        source: camera
        fillMode: Image.PreserveAspectFit
    }
}

I have installed the necessary packages :

$ sudo apt install qtmultimedia5-dev qtmultimedia5-examples qtmultimedia5-doc qml-module-qtmultimedia

But I have a blank window and the log gives me this :

(untitled1:5529): GStreamer-CRITICAL **: 12:35:35.378: gst_pad_get_current_caps: assertion 'GST_IS_PAD (pad)' failed

(untitled1:5529): GLib-GObject-CRITICAL **: 12:35:35.378: g_object_set: assertion 'G_IS_OBJECT (object)' failed

(untitled1:5529): GLib-GObject-CRITICAL **: 12:35:35.378: g_object_set: assertion 'G_IS_OBJECT (object)' failed
CameraBin error: "Erreur GStreamer : problème de négociation."
Unable to query the parameter info: QCameraImageProcessingControl::WhiteBalancePreset : "Argument invalide"
Unable to query the parameter info: QCameraImageProcessingControl::ColorTemperature : "Argument invalide"
Unable to query the parameter info: QCameraImageProcessingControl::ContrastAdjustment : "Argument invalide"
Unable to query the parameter info: QCameraImageProcessingControl::SaturationAdjustment : "Argument invalide"
Unable to query the parameter info: QCameraImageProcessingControl::SharpeningAdjustment : "Argument invalide"
CameraBin error: "Internal data stream error."

I actually have succeeded in running the app in my Ubuntu host machine but I have to recreate it in my VM.
Any help will be appreciated.
Thank you.

diego-qt

It is worth noting that I have installed the Extension pack for VirtualBox, I can check/uncheck the webcam in Devices menu and I can use the webcam with VLC with

$ vlc v4l2:///dev/video0

And if I add a log in the code, I can see that it detects the webcam, but it is not possible to load somehow.

SGaist

Hi,

What about accessing it with GStreamer directly since the error lies in there.

diego-qt

Hi @SGaist,
Do you mean testing out GStreamer from terminal or with Qt ? Do you have any documentation that could lead me there ? I had never heard of GStreamer

SGaist

A quick search returns this blog which contains several examples.

JoeCFD

@diego-qt GStreamer-CRITICAL **: 12:35:35.378: gst_pad_get_current_caps: assertion 'GST_IS_PAD (pad)' failed ===> this is gstreamer error message. That says Qt is using gstreamer underneath on Linux in multimedia module. From the message I can not tell what is wrong.

Check if you have installed all needed gstreamer libs and plugins.

from here
https://gstreamer.freedesktop.org/documentation/tutorials/basic/debugging-tools.html?gi-language=c
export GST_DEBUG=5( or 9)
to see more gstreamer logs