Camera example Freeze with QT6 on Ubuntu 22.04.1 when minimized or ApplicationDeactivate event.

MStackoverflo

Hi, I've seen I'm not the only one with the problem.

What happens is that when there's a QVideoWidget, and the app is either minimized or disappears because we clicked on another app, the QVideoWidget freezes and never recovers. Everything else is still working. Ex.: Hover button shows animation, clicks are sent, etc... The QVideoWdiget updates a frame when a picture is taken.

While the camera is running, I get this spammed in the application output tab, but I see the camera feed fine.
When I take picture, I get a "image is empty" warning sometimes.

qt.gui.imageio.jpeg: JPEG datastream contains no image
qt.gui.imageio.jpeg: JPEG datastream contains no image
Invalid texture upload for 0x55e799d1ef80 layer=0 mip=0

I'm using a Virtual Machine with Ubuntu 22.04.1. with wayland as the compositor and QT6.6

QTbug posts suggest it's a hardware acceleration problem, but I've tried with hardware acceleration turned off and I still get the issue.

I've tried the example with EDIT QT5.15.2 and the problem does not occur, but the frame rate is terrible.

Everything works as expected on Windows 11 and I don't get the qt.gui.imageio.jpeg: JPEG datastream contains no image problem.

Anyone have a clue on why?

MStackoverflo

I made it work using XCB instead of Wayland. For some reason, QT has a problem with Wayland. QT can run using XCB even though Ubuntu desktop uses wayland.

Before invoking QApplication in main, these line must be added :

qputenv("QT_QPA_PLATFORM","xcb");
qputenv("QT_MEDIA_BACKEND","gstreamer");

libxcb packages must be installed prior.

JoeCFD

@MStackoverflo On Ubuntu 22.04, default Qt version in the distribution is 5.15.3. Better to try 5.15.3. Qt5.12 is kind of old. I would not try Qt5.12 on Ubuntu 22.04. If you want to switch to Qt6, better to install Qt6.6 or above. Multimedia module has been reworked in Qt6.

MStackoverflo

@JoeCFD Hi, the QT6 version I'm trying is indeed QT6.6. The QT5 version I was trying was 5.15.2, the one that is available in the unified installer. I will rectify my post.

JoeCFD

@MStackoverflo Can you try Xorg(not wayland) first to see if the code works.
If your code does not work, post it here if possible. I can try it with both 5.15.3 and 6.6 for you.

MStackoverflo

@JoeCFD Hi, I tried with Xorg on Ubuntu by setting WaylandEnable=false in /etc/gdm3/custom.conf, but the QVideoWidget only shows one frame and freezes.

The camera example is here :
https://doc.qt.io/qt-6/qtmultimedia-camera-example.html
https://doc.qt.io/qt-5.15/qtmultimedia-multimediawidgets-camera-example.html

EDIT :
I'm developing an APP that uses that example's code, which is why I'm seeking help.

JoeCFD

@MStackoverflo Just tested. Both work fine with a camera.

MStackoverflo

@JoeCFD Nice. That means it may be a setup problem. Did you try on a Virtual Machine or original? Also, were you on ubuntu 22?

JoeCFD

@MStackoverflo Not in a virtual machine. I tried it on Lubuntu 22.04.

MStackoverflo

@JoeCFD I confirm that I cannot make it work on Ubuntu 22 when installed on a hard-drive. I get the same results. I'm currently trying to build on Lubuntu. Were you using wayland on Ubuntu? Because the default install I get is LXQt and uses x11. What is your setup?

MStackoverflo

@JoeCFD I try to run it on Lubuntu 22.04 LXQT with QT6.6 and it shows a blank black screen. I would like to know your setup. I have a fresh Lubuntu with sudo apt install build-essential libxcb*

JoeCFD

@MStackoverflo So many packages. I am not sure what you mean by setup. I use X11.

MStackoverflo

@JoeCFD Ok, the problem seems to be related in some ways to QT with wayland. Thank you for your time, it is very appreciated.

The app I need to develop is for Ubuntu 22 users, so it uses wayland.

Anyone has a clue on this setup?

MStackoverflo

I used gstreamer backend instead of ffmpeg and I no longer get the following error :

qt.gui.imageio.jpeg: JPEG datastream contains no image
qt.gui.imageio.jpeg: JPEG datastream contains no image
Invalid texture upload for 0x55e799d1ef80 layer=0 mip=0

Concerning video freeze, the window does not need to be minimized to freeze. If I slide another app over it to completely occlude it, it freezes. But, if there's even a small part showing, it doesn't freeze.

MStackoverflo

I made it work using XCB instead of Wayland. For some reason, QT has a problem with Wayland. QT can run using XCB even though Ubuntu desktop uses wayland.

Before invoking QApplication in main, these line must be added :

qputenv("QT_QPA_PLATFORM","xcb");
qputenv("QT_MEDIA_BACKEND","gstreamer");

libxcb packages must be installed prior.

JoeCFD

@MStackoverflo you may check if you have installed all wayland-related gstreamer packages. for example: gstreamer-gl-wayland-1.0.
and test some pipelines from command line. For example:
gst-launch-1.0 -v videotestsrc ! waylandsink