Resizing a constant Video stream from OpenCV to PyQt5 with QPainter in a QWidget using a Raspberry Pi

SGaist

With the code you show here, it seems you are getting lost.

You should take look at the QtMultimedia module samples before going further.

There's no need for QVideoWidget as QCameraViewfinder is already a QVideoWidget. You also don't need for two separated classes.

Xenoshell

Ok, i looked at the multimedia samples and learned a bit from them. Sadly the code is all c++ and not python so i couldnt get that much out of it, besides that i should use (maybe) QMainWindow.
I put some tests in my code and the "Segmentation fault" error seems to be a big problem somewhere in the startVid() function. The CaptureMode(0) is sadly not supported and i have to use CaptureMode(2). Could this be a problem? Anyway, thanks for all the support from you, as always here is my code:

import sys
from PyQt5 import QtCore , QtWidgets, QtGui, QtMultimedia, QtMultimediaWidgets
from PyQt5.QtCore import QObject, pyqtSignal
from PyQt5.QtWidgets import QApplication
from PyQt5.QtMultimedia import QCamera, QCameraInfo, QMediaObject, QCameraViewfinderSettings
from PyQt5.QtMultimediaWidgets import QCameraViewfinder


class Camera(QObject):
    def __init__(self, parent = QObject()):
        super(Camera, self).__init__(parent)
        self.obj = QObject()
        self.cam = QCamera(self.obj)
        self.caminfo = QCameraInfo(self.cam)
        self.camvfind = QCameraViewfinder()
        self.camvfindset = QCameraViewfinderSettings()
        self.cammode = self.cam.CaptureMode(2)

    def iniCamera(self):
        print(self.caminfo.description())
        print(self.caminfo.availableCameras())
        
        if self.cam.isCaptureModeSupported(self.cammode):
            print("Capturemode supported")
            self.cam.setCaptureMode(self.cammode)
        
        if self.caminfo.isNull() != self.caminfo.defaultCamera():
            self.cam = QCamera(self.caminfo.defaultCamera())
            self.cam.load()
            
            self.cam.start()
    
    def startVid(self):
   
        self.cam.setViewfinder(self.camvfind)
        self.camvfindset.setResolution(1280,720)
        print("self.cam.supportedViewfinderFrameRateRanges(self.camvfind)")
        self.camvfindset.setMinimumFrameRate(15)
        self.camvfind.show()
           


if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    
    cam = Camera()
    
    cam.iniCamera()
    
    cam.startVid()
   
    
    sys.exit(app.exec_())

PS: i actually managed to open a window, but sadly its just black and doesnt show up consistent.

SGaist

What is the use of self.obj ?

if self.caminfo.isNull() != self.caminfo.defaultCamera(): You are comparing a boolean with a QCameraInfo object.

Then you are replace your current cam object with a new so your capture mode related code is useless.

You should start by just translating the QCameraViewfinder example to python.

Xenoshell

@SGaist Ok i did translate the example to python and it actually did alot. Now a window with the camera feed pops up. Unfortunatly its not very consistent since sometimes the ol' Segmentation fault error still shows and then no window opens. I think thats very strange.
Also when the camera feed opens the terminal output is:

** (python3:1197): WARNING **: Error retrieving accessibility bus address: org.freedesktop.DBus.Error.ServiceUnknown: The name org.a11y.Bus was not provided by any .service files
Venus USB2.0 Camera
[<PyQt5.QtMultimedia.QCameraInfo object at 0x72fafa30>]
Capturemode supported
QWidget::paintEngine: Should no longer be called
QWidget::paintEngine: Should no longer be called

Whats up with QWidget::paintEngine: Should no longer be called?
Do you know how i could add buttons to this window? Do i guess i need layers and a MainWindow, but where should i look for more information?
As always here is my code:

import sys
from PyQt5 import QtCore , QtWidgets, QtGui, QtMultimedia, QtMultimediaWidgets
from PyQt5.QtCore import QObject, pyqtSignal
from PyQt5.QtWidgets import QApplication
from PyQt5.QtMultimedia import QCamera, QCameraInfo, QMediaObject, QCameraViewfinderSettings, QCameraImageCapture
from PyQt5.QtMultimediaWidgets import QCameraViewfinder


class Camera(QObject):
    def __init__(self, parent = QObject()):
        super(Camera, self).__init__(parent)
        self.cam = QCamera()
        self.caminfo = QCameraInfo(self.cam)
        self.camvfind = QCameraViewfinder()
        self.camvfindset = QCameraViewfinderSettings()
        self.cammode = self.cam.CaptureMode(1)
        self.camimgcap = QCameraImageCapture(self.cam)

    def iniCamera(self):
        print(self.caminfo.description())
        print(self.caminfo.availableCameras())
        
        if self.cam.isCaptureModeSupported(self.cammode):
            print("Capturemode supported")
            
    
    def startVid(self):
        
        self.camvfind.show()
        
        self.cam.setViewfinder(self.camvfind)
        
        self.cam.load()
        self.camvfindset.setResolution(1280,720)
        #print(self.cam.supportedViewfinderFrameRateRanges(self.camvfind))
        self.camvfindset.setMinimumFrameRate(15)
        
        self.cam.setCaptureMode(self.cammode)
        self.cam.start()
        
        #self.cam.unload()


if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    
    cam = Camera()
    
    cam.iniCamera()
    
    cam.startVid()
    
    del cam
    
    sys.exit(app.exec_())

SGaist

Why are you calling del cam just before sys.exit(app.exec_()) ?

Xenoshell

I just tried if it would solve the "Segmentation fault" error but it didnt work.
Well can you give me another point in the right direction?

SGaist

Don't delete objects while you are using them ;)

Can you get a stack trace of the crash ?

Xenoshell

Ok, it seems like its not possible to catch a Segmentation fault error with stack trace. I used "gdb" to get some information about the error. Here is the output:

(gdb) run qt.py 
Starting program: /usr/bin/python3 qt.py
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".
[New Thread 0x720a7470 (LWP 20003)]
[New Thread 0x716ff470 (LWP 20004)]

** (python3:19975): WARNING **: Error retrieving accessibility bus address: org.freedesktop.DBus.Error.ServiceUnknown: The name org.a11y.Bus was not provided by any .service files
[New Thread 0x6ff00470 (LWP 20007)]
[New Thread 0x6f5ff470 (LWP 20008)]
[New Thread 0x6e6ab470 (LWP 20022)]
[Thread 0x6e6ab470 (LWP 20022) exited]
[New Thread 0x6e6ab470 (LWP 20023)]
[Thread 0x6e6ab470 (LWP 20023) exited]
Venus USB2.0 Camera
[<PyQt5.QtMultimedia.QCameraInfo object at 0x72fde030>]
Capturemode supported

Thread 1 "python3" received signal SIGSEGV, Segmentation fault.
0x7344b620 in platform_get_handle () from /opt/vc/lib/libEGL.so

I read many threads about this problem and it could be that i run out of memory. Since Geany-Output is:

Segmentation fault
------------------
(program exited with code: 139)
Press return to continue

and code :139 means "attempt to access a virtual address which is not in your address space"

EDIT: the problem could also occur because some of the modules are written in C++. I read that some problems can happen because of this

here is more output of gdb that "should" give more info

(gdb) bt
#0  0x733d4620 in platform_get_handle () from /opt/vc/lib/libEGL.so
#1  0x733c9f2c in eglCreateWindowSurface () from /opt/vc/lib/libEGL.so
#2  0x722e7004 in ?? ()
   from /usr/lib/arm-linux-gnueabihf/qt5/plugins/xcbglintegrations/libqxcb-egl-integration.so
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

Xenoshell

Ok, well i can give you some more info. It seems that the Segmentation fault is because of this line self.camvfind.show() or the line after that. I just tested this with putting print("1") after every line and looking how many lines of 1s get printed.

Also someone from stackoverflow wrote this :"Most likely there is a race condition in some of the modules you load and someone accesses memory before someone else has set it up. It looks like the program is looking for a handle in libEGL and that function is triggering the segfault."
This person also suggested that i look at the memory load of the program but it doesnt seem to matter because the memory load is sometimes high and it works and sometimes its lower and it doesnt work

SGaist

Do you have several versions of Qt installed on your device ?

Xenoshell

I have qt5 and qt4 but i deinstalled qt4 and some folders are still left. They are in: /usr/lib/arm-linux-gnueabihf/qt4
/usr/share/qt4
Also output of qmake --version is :

QMake version 3.0
Using Qt version 5.7.1 in /usr/lib/arm-linux-gnueabihf

SGaist

How did you install PyQt ?

Xenoshell

I tried to install PyQt from source but it always gave me an error so i just used sudo apt-get install pyqt5-dev/pyqt5-dev-tools/python3-pyqt5.qtmultimedia.
I also wrote my question with Segmentation Fault on other forums and someone said: "There is a buffer overflow happening in the eglCreateWindowSurface function". To be honest i dont know exactly what to do with this or how this would help me with my problem. The eglCreateWindowSurface function has something with openGl to do, maybe there is a problem with it? You got an idea?

SGaist

Do you have the latest version of Raspbian running ?

Xenoshell

Yeah i feel like i do sudo apt-get update && upgrade at least once a day. I just checked about SIP and i compiled it from source but i cant remember if i actually used the command make and make install. Does that mean i have to reinstall pyqt5 again? I guess i just open a new thread. Thanks for all the help @SGaist