PyQt5 VideoPlayer: Converting to Object Orientated Code Prevents Playback - python-3.x

Question

I've been looking into how to incorporate a video or livestream into an app. I have found some functional code that works fine:
from PyQt5.QtGui import *
from PyQt5.QtCore import *
from PyQt5.QtWidgets import *
import cv2 # OpenCV
import qimage2ndarray # for a memory leak,see gist
import sys # for exiting
# Minimal implementation...
def displayFrame():
ret, frame = cap.read()
frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
image = qimage2ndarray.array2qimage(frame)
label.setPixmap(QPixmap.fromImage(image))
app = QApplication([])
window = QWidget()
# OPENCV
cap = cv2.VideoCapture("Vid.mp4")
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 320)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 240)
# timer for getting frames
timer = QTimer()
timer.timeout.connect(displayFrame)
timer.start(60)
label = QLabel('No Camera Feed')
button = QPushButton("Quiter")
button.clicked.connect(sys.exit) # quiter button
layout = QVBoxLayout()
layout.addWidget(button)
layout.addWidget(label)
window.setLayout(layout)
window.show()
app.exec_()
And I am trying to be able to use this in some object orientated code, with the aim of creating a video playback widget to incorporate into other apps:
import cv2
import sys
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
import qimage2ndarray # for a memory leak,see gist
import sys # for exiting
# Minimal implementation...
class basicWindow(QMainWindow):
def __init__(self):
super(basicWindow, self).__init__()
# OPENCV
cap = cv2.VideoCapture("Vid.mp4")
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 320)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 240)
# timer for getting frames
timer = QTimer()
timer.timeout.connect(displayFrame)
timer.start(60)
label = QLabel('No Camera Feed')
button = QPushButton("Quiter")
button.clicked.connect(sys.exit) # quiter button
layout = QVBoxLayout()
layout.addWidget(button)
layout.addWidget(label)
widget = QWidget()
widget.setLayout(layout)
self.setCentralWidget(widget)
def displayFrame():
ret, frame = cap.read()
if ret:
frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
image = qimage2ndarray.array2qimage(frame)
try:
label.setPixmap(QPixmap.fromImage(image))
except Exception as e:
print(e)
if __name__ == '__main__':
app = QApplication(sys.argv)
windowExample = basicWindow()
windowExample.show()
sys.exit(app.exec_())
I'm new to both OO coding and PyQt5, so any advice on how I'm either misinterpreting how the code works or what Im missing would be great. I have tried already setting label to a global variable, as I wasnt sure the function displayFrame() was aware of what label to change with label.setPixmap, but otherwise Im a little lost.

Answer 1

In your first example it works because label is a global variable, so displayFrame can access it as such.
In the other case, label is only declared in the scope of the __init__ of the basicWindow instance, so displayFrame knows nothing about it.
Make label a member of the instance (self.label = QLabel()), displayFrame a method of the basicWindow class (def displayFrame(self):) and then access the label correctly; note that you also need to make both cap and timer member of the instance (self), otherwise their objects will be immediately "garbage collected" after __init__ returns.
class basicWindow(QMainWindow):
def __init__(self):
super(basicWindow, self).__init__()
# ...
self.cap = cv2.VideoCapture("Vid.mp4")
# ...
self.timer = QTimer()
self.timer.timeout.connect(self.displayFrame)
self.timer.start(60)
self.label = QLabel('No Camera Feed')
# ...
def displayFrame(self):
ret, frame = self.cap.read()
if ret:
frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
image = qimage2ndarray.array2qimage(frame)
try:
self.label.setPixmap(QPixmap.fromImage(image))
except Exception as e:
print(e)
Since you're new to OO programming, I suggest you to start by studying how classes and instances and name resolution work in python.