core: improved handling of camera & video errors

1. Display error message in the video area in the following
cases (runtime error detection during frame reading):
  a. Camera is unavailable
 (at initialization or gets disconnected during use).
  b. Prerecorded video can't be played
 (file doesn't exist or video stream gets interrupted/corrupted).
Created a dedicated "display_error_message()" method
to display a visual error message in the exact same location
where the video would appear.
It uses a black background with a red border to match the UI styling.
Shows white text that's bold and centered for clear readability.
Maintains the exact same dimensions as the video area (321x331 pixels).
The error handling ensures the application won't crash and provides
a clear feedback to users about what went wrong,
making the dashboard much more user-friendly and robust.

2. Hardware consideration - a more reliable camera detection.
Added a small delay (0.1 seconds), to give camera time
to initialize properly. Cameras (especially USB cameras) often need
a brief moment to become fully operational
after a "cv2.VideoCapture()" call.
This ensures camera is ready before "view_video()" starts
getting called every 20ms, which reduces false negatives where
camera exists but isn't ready yet.

Documentation was updated accordingly and a screenshot displaying
the camera error was added to the "README.md" file.

Co-authored-by: Cursor AI

Signed-off-by: Pavel Bar <pbar@redhat.com>

Author: barpavel

README.md

@@ -24,9 +24,11 @@ Welcome to the Car Dashboard (HMI) prototype project! This simple yet intuitive
 
 7. **Camera Streaming**
    - Access live camera feeds for improved awareness and safety.
+   - Handles camera failures (camera is unavailable or gets disconnected during use).
 
 8. **Prerecorded Video Streaming**
    - When camera is unavailable (i.e., during development or demos), you can play video instead.
+   - Handles video file failures (file doesn't exist or video stream gets interrupted/corrupted).
 
 ## Development
 
@@ -79,6 +81,7 @@ options:
 <img src = "ss/2.PNG">
 <img src = "ss/3.PNG">
 <img src = "ss/4.PNG">
+<img src = "ss/5.PNG">
 
 ## Todo
 

app.py

@@ -5,6 +5,7 @@
 
 import io
 import sys
+import time
 import argparse
 
 # import OpenCV module
@@ -15,7 +16,7 @@
 # PyQt5 imports - Core
 from PyQt5.QtCore import QRect, QSize, QTimer, Qt, QCoreApplication, QMetaObject
 # PyQt5 imports - GUI
-from PyQt5.QtGui import QPixmap, QImage, QFont
+from PyQt5.QtGui import QPixmap, QImage, QFont, QPainter, QPen
 # PyQt5 imports - Widgets
 from PyQt5.QtWidgets import (
     QApplication, QWidget, QHBoxLayout, QLabel, QFrame, QPushButton,
@@ -693,6 +694,31 @@ def setupUi(self, MainWindow):
 )
         self.label_km.setAlignment(Qt.AlignCenter)
 
+    def display_error_message(self, message):
+        """Display error message in the video area with proper styling."""
+        # Create a QPixmap with the same dimensions as the webcam area
+        error_pixmap = QPixmap(Ui_MainWindow.WEBCAM_WIDTH, Ui_MainWindow.WEBCAM_HEIGHT)
+        error_pixmap.fill(Qt.black)  # Black background to match the UI
+
+        # Draw the error message on the pixmap
+        painter = QPainter(error_pixmap)
+        painter.setPen(QPen(Qt.red, 2))
+        painter.setFont(QFont("Arial", 12, QFont.Bold))
+
+        # Draw border
+        painter.drawRect(2, 2, Ui_MainWindow.WEBCAM_WIDTH - 4, Ui_MainWindow.WEBCAM_HEIGHT - 4)
+
+        # Draw error message in center
+        painter.setPen(QPen(Qt.white, 1))
+        text_rect = error_pixmap.rect()
+        text_rect.adjust(10, 0, -10, 0)  # Add some margin
+        painter.drawText(text_rect, Qt.AlignCenter | Qt.TextWordWrap, message)
+
+        painter.end()
+
+        # Set the error pixmap to the webcam label
+        self.webcam.setPixmap(error_pixmap)
+
     @staticmethod
     def _read_video_frame():
         """Read and validate a video frame from the capture device.
@@ -709,6 +735,7 @@ def _read_video_frame():
         return image
 
     def view_video(self):
+        """Displays camera / video stream and handles errors."""
         image = Ui_MainWindow._read_video_frame()
 
         # Check if frame is valid
@@ -719,11 +746,13 @@ def view_video(self):
                 cap.set(cv2.CAP_PROP_POS_FRAMES, 0)
                 image = Ui_MainWindow._read_video_frame()
                 if image is None:
-                    # If still no frame, stop the timer
+                    # If still no frame, show error and stop the timer
+                    self.display_error_message("Video file is unavailable or corrupted!\n\nPlease check video file.")
                     self.quit_video()
                     return
             else:
-                # For camera, stop the timer
+                # For camera, show error and stop the timer
+                self.display_error_message("Camera is unavailable!\n\nPlease check camera connection.")
                 self.quit_video()
                 return
 
@@ -767,6 +796,8 @@ def controlTimer(self):
                 cap = cv2.VideoCapture(self.video_path)
             else:
                 cap = cv2.VideoCapture(0)
+                # Give camera time to initialize for better robustness
+                time.sleep(0.1)
             self.timer.start(20)
 
     def retranslateUi(self, MainWindow):