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.