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



  • So i found this python code that fits in some ways for my project. Now i want to change everything that annoys me.
    My requirements:

    • Videostream with 1920x1080 or 1280x720 resolution
    • 2 Buttons within the QWidget right beside/under the Videostream (doesnt matter too much)
      Right now i wanna focus on getting the right resolution. I already read something about QWidget.resize (self, int w, int h) and i wonder if i can use it for my problem and where in the code i could implement it. I appreciate any help i get, even if it just points me in the right direction
    #Importing necessary libraries, mainly the OpenCV, and PyQt libraries
    import cv2
    import numpy as np
    import sys
    from PyQt5 import QtCore
    from PyQt5 import QtWidgets
    from PyQt5 import QtGui
    from PyQt5.QtCore import pyqtSignal
     
    class ShowVideo(QtCore.QObject):
     
        #initiating the built in camera
        camera_port = 0
        camera = cv2.VideoCapture(camera_port)
        VideoSignal = QtCore.pyqtSignal(QtGui.QImage)
        
     
        def __init__(self, parent = None):
            super(ShowVideo, self).__init__(parent)
     
        @QtCore.pyqtSlot()
        def startVideo(self):
     
            run_video = True
            while run_video:
                ret, image = self.camera.read()
     
                color_swapped_image = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
     
                height, width, _ = color_swapped_image.shape
                
                #width = camera.set(CAP_PROP_FRAME_WIDTH, 1600)
    			#height = camera.set(CAP_PROP_FRAME_HEIGHT, 1080)
    			#camera.set(CAP_PROP_FPS, 15)
     
                qt_image = QtGui.QImage(color_swapped_image.data,
                                        width,
                                        height,
                                        color_swapped_image.strides[0],
                                        QtGui.QImage.Format_RGB888)
     
                self.VideoSignal.emit(qt_image)
     
     
    class ImageViewer(QtWidgets.QWidget):
        def __init__(self, parent = None):
            super(ImageViewer, self).__init__(parent)
            self.image = QtGui.QImage()
            self.setAttribute(QtCore.Qt.WA_OpaquePaintEvent)
     
     
        def paintEvent(self, event):
            painter = QtGui.QPainter(self)
            painter.drawImage(0,0, self.image)
            self.image = QtGui.QImage()
     
        def initUI(self):
            self.setWindowTitle('Test')
     
        @QtCore.pyqtSlot(QtGui.QImage)
        def setImage(self, image):
            if image.isNull():
                print("Viewer Dropped frame!")
     
            self.image = image
            if image.size() != self.size():
                self.setFixedSize(image.size())
            self.update()
     
     
    if __name__ == '__main__':
     
        app = QtWidgets.QApplication(sys.argv)
        thread = QtCore.QThread()
        thread.start()
        vid = ShowVideo()
        vid.moveToThread(thread)
        image_viewer = ImageViewer()
     
        vid.VideoSignal.connect(image_viewer.setImage)
     
        #Button to start the videocapture:
     
        push_button1 =QtWidgets.QPushButton('Start')
        push_button2 = QtWidgets.QPushButton('Test')
        push_button1.clicked.connect(vid.startVideo)
        vertical_layout = QtWidgets.QVBoxLayout()
        
     
        vertical_layout.addWidget(image_viewer)
        vertical_layout.addWidget(push_button1)
        vertical_layout.addWidget(push_button2)
     
        layout_widget = QtWidgets.QWidget()
        layout_widget.setLayout(vertical_layout)
     
        main_window = QtWidgets.QMainWindow()
        main_window.setCentralWidget(layout_widget)
        main_window.show()
        sys.exit(app.exec_())
    

  • Lifetime Qt Champion

    Hi and welcome to devnet,

    What version of Qt are you using ?
    On what OS ?
    What do you mean by right resolution ?
    Why not use Qt's multimedia module ?
    What size is the video stream you get from the camera ?



  • Hello SGaist,
    I am using Qt5 on Raspbian, but i also have Qt4. My project is building a functioning microscope that uses a raspberry pi. So i need the python file in autostart(which is no problem i guess). So the right resolution is full screen with room for 2 extra buttons for the whole program. Unfortunatly the camera only can stream in those resolutions 1920x1080, 1280x720, 640x480. Also it uses the AVI videoformat.
    To be honest i read about Qt's multimedia module but didnt put much time into it. Is it a much easier option for me? I dont need to change the frames of my live stream so i wouldnt mind using something else.
    I dont know for sure what size i get from the video stream but i guess its 640x480 because its quite small.

    Thanks for the fast answer and i hope you can give me some guidance.

    EDIT: i searched for pyqt5 code in python but cant find much about it besides some links to the c++ equivalent

    EDIT2: OK, i looked around for the multimedia module and it seems like i need to use QCamera. So what do i need to display the output of QCamera? QVideoWidget?


  • Lifetime Qt Champion



  • Hello again,
    I worked with your answer in the right direction and am now at the next problem.
    My Error:

    QObject::startTimer: Timers can only be used with threads started with QThread
    QObject::startTimer: Timers can only be used with threads started with QThread
    <built-in method description of QCameraInfo object at 0x72f56970>
    Traceback (most recent call last):
      File "qt.py", line 29, in <module>
        cam.iniCamera(qcam, qcaminfo)
      File "qt.py", line 20, in iniCamera
        cam = QCamera(caminfo.deviceName())
    TypeError: arguments did not match any overloaded call:
      QCamera(parent: QObject = None): argument 1 has unexpected type 'str'
      QCamera(Union[QByteArray, bytes, bytearray], parent: QObject = None): argument 1 has unexpected type 'str'
      QCamera(QCameraInfo, parent: QObject = None): argument 1 has unexpected type 'str'
      QCamera(QCamera.Position, parent: QObject = None): argument 1 has unexpected type 'str'
    

    and my code:

    #import numpy as np
    import sys
    from PyQt5 import QtCore , QtWidgets, QtGui, QtMultimedia
    from PyQt5.QtMultimedia import QCamera, QCameraInfo, QMediaObject
    #from PyQt5.QtWidgets import QtVideoWidget
    #from PyQt5 import QtMediaObject
    from PyQt5.QtCore import pyqtSignal
    
    class Camera:
        def __init__(self):
            #super(Camera, self).__init__(parent)
            self.cam = QCamera()
            self.caminfo = QCameraInfo()
    
        def iniCamera(self, cam, caminfo):
            print (caminfo.description)
            
            if caminfo.isNull() != True:
               cam = QCamera(caminfo.deviceName())
               print (caminfo.description)
    
    
    if __name__ == '__main__':
        cam = Camera()
        qcam = QCamera()
        qcaminfo = QCameraInfo(qcam)
        
        cam.iniCamera(qcam, qcaminfo)
    

    I know i can use super(Camera, self).init(parent) and def init(self, parent) and the error disappears but another one occurs:

    TypeError: __init__() missing 1 required positional argument: 'parent'
    

    Do you have any idea what my problem is?


  • Lifetime Qt Champion

    You Camera class is not based on QObject hence your "parent" error.



  • Hello @SGaist,
    here i am again and i made quite some progress, or at least i think.
    I get no real error but i still have some questions.
    How can i connect QCameraViewFinder with QCamera and QVideoWidget?
    How is my code looking?
    Should i do something specific in a very special way that is maybe hard for a beginner?
    Do you have some tips for me at this point of my project?
    Thanks again for all the help you have given me :)

    #import numpy as np
    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
    from PyQt5.QtMultimediaWidgets import QVideoWidget, QCameraViewfinder
    
    
    class Camera(QObject):
        def __init__(self, parent):
            super(Camera, self).__init__(parent)
            self.obj = QObject()
            self.cam = QCamera(self.obj)
            self.caminfo = QCameraInfo(self.cam)
    
        def iniCamera(self, cam, caminfo):
            print (caminfo.description())
            print(caminfo.availableCameras())
            
            if caminfo.isNull() != caminfo.defaultCamera():
               cam = QCamera(caminfo.defaultCamera())
               cam.start()
               
    class VideoPlayaa():
    	def __init__(self):
    		self.vid = QVideoWidget()
    		self.camvfind = QCameraViewfinder(self.vid)
     
        def startVid(self,vid,camvfind,cam):
            
    
    
    if __name__ == '__main__':
        app = QtWidgets.QApplication([])
        
        obj = QObject()
        cam = Camera(obj)
        qcam = QCamera()
        qcaminfo = QCameraInfo(qcam)
        
        vid = VideoPlayaa()
        
        cam.iniCamera(qcam, qcaminfo)
        
        app.exec_()
    

  • Lifetime Qt Champion

    QCameraViewfinder is a QVideoWidget.

    Call camera.setViewfinder(viewfinder)



  • Ok i tried to implement this into my code but i am pretty sure i am still missing something for displaying the actual video. Also i am getting the Error: Segmentation fault.
    Here is my code, i tried to clean it a little bit up:

    #import numpy as np
    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
    from PyQt5.QtMultimediaWidgets import QVideoWidget, 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.cam.CaptureMode(0)
    
        def iniCamera(self):
            print (self.caminfo.description())
            print(self.caminfo.availableCameras())
            
            if self.caminfo.isNull() != self.caminfo.defaultCamera():
                self.cam = QCamera(self.caminfo.defaultCamera())
                self.cam.load()
                self.cam.start()
               
    class VideoPlayaa(QObject):
        def __init__(self, parent = QObject()):
            super(VideoPlayaa, self).__init__(parent)
            self.vid = QVideoWidget()
            self.camvfind = QCameraViewfinder(self.vid)
            self.cam = QCamera()
    
        def startVid(self):
       
                self.cam.setViewfinder(self.camvfind)
                self.camvfind.show()
                
            
    
    
    if __name__ == '__main__':
        app = QtWidgets.QApplication([])
        
        cam = Camera() 
        cam.iniCamera()
        
        vid = VideoPlayaa()
        vid.startVid()
        
        
        app.exec_()
    

    Can you tell me how to progress with my project? How do i insert camera.setViewfinder(viewfinder) in a window? Should i maybe start a new thread because the original question is now rather unimportant?


  • Lifetime Qt Champion

    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.



  • 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.


  • Lifetime Qt Champion

    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.



  • @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_())
    

  • Lifetime Qt Champion

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



  • 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?


  • Lifetime Qt Champion

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

    Can you get a stack trace of the crash ?



  • 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?)
    


  • 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


  • Lifetime Qt Champion

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



  • 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
    
    

  • Lifetime Qt Champion

    How did you install PyQt ?



  • 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?


  • Lifetime Qt Champion

    Do you have the latest version of Raspbian running ?



  • 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



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