Webcam preview with Qt Quick

[Aras]

@jerome_isAviable I am using the declarative camera sample app that comes with Qt installation without any modification, so I assume this is not an error in the code, but something with my environment.

I am using Ubuntu Linux 16.06 64bit. Here is are my gstreamer packages:

$ sudo dpkg -l |grep gstreamer
ii  gir1.2-gstreamer-1.0                            1.8.2-1~ubuntu1                                             amd64        GObject introspection data for the GStreamer library
ii  gstreamer-qapt                                  3.0.2-0ubuntu1.1                                            amd64        GStreamer plugin to install codecs using QApt
ii  gstreamer1.0-alsa:amd64                         1.8.2-1ubuntu0.1                                            amd64        GStreamer plugin for ALSA
ii  gstreamer1.0-clutter-3.0                        3.0.18-1                                                    amd64        Clutter PLugin for GStreamer 1.0
ii  gstreamer1.0-fluendo-mp3:amd64                  0.10.32.debian-1                                            amd64        Fluendo mp3 decoder GStreamer 1.0 plugin
ii  gstreamer1.0-libav:amd64                        1.8.2-1~ubuntu1                                             amd64        libav plugin for GStreamer
ii  gstreamer1.0-plugins-bad:amd64                  1.8.2-1ubuntu0.1                                            amd64        GStreamer plugins from the "bad" set
ii  gstreamer1.0-plugins-bad-faad:amd64             1.8.2-1ubuntu0.1                                            amd64        GStreamer faad plugin from the "bad" set
ii  gstreamer1.0-plugins-bad-videoparsers:amd64     1.8.2-1ubuntu0.1                                            amd64        GStreamer videoparsers plugin from the "bad" set
ii  gstreamer1.0-plugins-base:amd64                 1.8.2-1ubuntu0.1                                            amd64        GStreamer plugins from the "base" set
ii  gstreamer1.0-plugins-base-apps                  1.8.2-1ubuntu0.1                                            amd64        GStreamer helper programs from the "base" set
ii  gstreamer1.0-plugins-good:amd64                 1.8.2-1ubuntu0.1                                            amd64        GStreamer plugins from the "good" set
ii  gstreamer1.0-plugins-ugly:amd64                 1.8.2-1ubuntu0.1                                            amd64        GStreamer plugins from the "ugly" set
ii  gstreamer1.0-plugins-ugly-amr:amd64             1.8.2-1ubuntu0.1                                            amd64        GStreamer plugins from the "ugly" set
ii  gstreamer1.0-pulseaudio:amd64                   1.8.2-1ubuntu0.1                                            amd64        GStreamer plugin for PulseAudio
ii  gstreamer1.0-tools                              1.8.2-1~ubuntu1                                             amd64        Tools for use with GStreamer
ii  gstreamer1.0-x:amd64                            1.8.2-1ubuntu0.1                                            amd64        GStreamer plugins for X11 and Pango
ii  libgstreamer-plugins-bad1.0-0:amd64             1.8.2-1ubuntu0.1                                            amd64        GStreamer development files for libraries from the "bad" set
ii  libgstreamer-plugins-base1.0-0:amd64            1.8.2-1ubuntu0.1                                            amd64        GStreamer libraries from the "base" set
ii  libgstreamer-plugins-good1.0-0:amd64            1.8.2-1ubuntu0.1                                            amd64        GStreamer development files for libraries from the "good" set
ii  libgstreamer1.0-0:amd64                         1.8.2-1~ubuntu1                                             amd64        Core GStreamer libraries and elements
ii  libreoffice-avmedia-backend-gstreamer           1:5.1.4-0ubuntu1                                            amd64        GStreamer backend for LibreOffice
ii  phonon-backend-gstreamer:amd64                  4:4.8.2-0ubuntu2                                            amd64        Phonon GStreamer 1.0 backend
ii  phonon-backend-gstreamer-common:amd64           4:4.8.2-0ubuntu2                                            amd64        Phonon GStreamer 1.0.x backend icons
ii  phonon4qt5-backend-gstreamer:amd64              4:4.8.2-0ubuntu2                                            amd64        Phonon Qt5 GStreamer 1.0 backend

Sorry for the late reply guys! I did not realize you had replied. I just enabled email notification in my profile for this forum (they were disabled by default). I appreciate your help!

[Aras]

Here is the application output in Qt Creator:

Starting /home/aras/Qt5.7.0/Examples/Qt-5.7/multimedia/build-declarative-camera-Desktop_Qt_5_7_0_GCC_64bit-Debug/declarative-camera...
QML debugging is enabled. Only use this in a safe environment.
defaultServiceProvider::requestService(): no service found for - "org.qt-project.qt.camera"
defaultServiceProvider::requestService(): no service found for - "org.qt-project.qt.mediaplayer"
qrc:///VideoCaptureControls.qml:110: Error: Cannot assign [undefined] to QString
qrc:///CameraListButton.qml:65:5: QML CameraListPopup: Binding loop detected for property "currentValue"
qrc:///PhotoCaptureControls.qml:135: Error: Cannot assign [undefined] to QString
qrc:///CameraListButton.qml:65:5: QML CameraListPopup: Binding loop detected for property "currentValue"
/home/aras/Qt5.7.0/Examples/Qt-5.7/multimedia/build-declarative-camera-Desktop_Qt_5_7_0_GCC_64bit-Debug/declarative-camera exited with code 0

[SGaist]

IIRC, the gstreamer backend is built against 0.1 so one thing you could do is re-build the plugin against 1.0.

[Aras]

@SGaist can you elaborate how I could do that? It there a Qt module that I need to rebuild and reinstall?

[SGaist]

The QtMultimedia module provides the backends. You don't need to rebuild the whole module, just the gstreamer backend.

You can grab the sources from the installer to get you started.

[Aras]

I went into software repository and installed anything matching gstreamer1.0* and then tried running the sample app again. Now the video is working. So it was a dependancy on one of the gstreamer1.0 packages. Unfortunately I dont know which one.

Thank you for your help @SGaist and @jerome_isAviable !

[Aras]

I am now having this exact problem on a second machine. Searching through repository for any packages related to gstreamer and installing them -- it seems so ad hoc!

Is there any way to see in Qt Creator or in the application output what library should be providing the camera service? That way I can just install that library instead of the other 200 and be sure I got it right. Any suggestions?

[SGaist]

I'm not 100% sure but I think it's the gst-plugins-good package.

[Aras]

Thanks for the hint @SGaist ! On this new install it was the gstreamer0.10-plugins-good set that I was missing. I had the version 1.0 installed instead of 0.1.

I am going to mark this thread as resolved, but I still would like to know if there is a better way to figure out what library is missing. So if you know, please chime in! Thanks!

[SGaist]

You're welcome !

If you would like to use the latest version of gstreamer, you'll likely have to re-build the QtMultimedia backend.