Python2.7下OpenCV停车场空位/行人检测程序无输出求助（Exit Code 0）

Hey there, let's work through why your program is exiting cleanly (exit code 0) but not showing any video or drawing those detection markers. I've dealt with similar headaches in older Python/OpenCV setups, so here are the most common fixes to get your program up and running:

1. Verify Your Video File is Loading Correctly #

OpenCV's VideoCapture fails silently if it can't find or read your input video—this is the #1 culprit for this issue.

• Move your video file into the same folder as your script, then use just the filename (no complex paths) to load it:

  cap = cv2.VideoCapture("input_video.mp4")
  

• Add a quick check to confirm the video opened successfully:

  if not cap.isOpened():
      print("Error: Could not open video file!")
      exit(1)
  

• Avoid paths with non-ASCII characters (like Chinese) in Python 2.7—its string handling can struggle with these, leading to hidden loading failures.

2. Fix Your Window Display Loop #

OpenCV requires cv2.waitKey() to handle window events—without it, your video window will either flash briefly or never show up at all.

• Make sure your main loop follows this structure:

  while cap.isOpened():
      ret, frame = cap.read()
      if not ret:
          break  # Exit loop when video ends
      
      # Insert your parking spot/pedestrian detection and drawing code here
      # For testing, add a simple text overlay to confirm drawing works:
      cv2.putText(frame, "Video is playing!", (50, 50), cv2.FONT_HERSHEY_SIMPLEX, 1, (0, 255, 0), 2)
      
      cv2.imshow("Parking Detection", frame)
      # Wait 25ms between frames (adjust for your video's FPS) and quit on 'q' press
      if cv2.waitKey(25) & 0xFF == ord('q'):
          break
  
  # Clean up resources after the loop
  cap.release()
  cv2.destroyAllWindows()
  

• If you set waitKey(0), it will pause on each frame until you press a key—use this for debugging individual frames.

3. Check OpenCV-Python 2.7 Compatibility #

Python 2.7 is end-of-life, so newer OpenCV versions (4.x+) don't support it. This can cause silent failures even if imports seem to work.

• Install a compatible version:

  pip install opencv-python==3.4.2.16
  

• Verify your installation in a Python shell:

  import cv2
  print(cv2.__version__)  # Should show 3.4.2.16 or similar
  

4. Debug Your Detection & Drawing Logic #

If the video shows up but no markers appear, your detection code might not be executing correctly:

• Comment out all detection logic first—just show the raw video. If that works, re-enable parts of the code one by one to find where it breaks.
• Double-check that your drawing functions (like cv2.rectangle() or cv2.circle()) are using valid coordinates and visible colors (e.g., bright green/red against your video background).

5. Check for Window Visibility Issues #

Sometimes the OpenCV window gets hidden behind other apps, or won't show up in headless environments:

• Close all other windows to make sure your detection window isn't buried.
• If you're running this on a server without a GUI, you'll need to use OpenCV's headless mode (but that won't display a window—stick to a local desktop setup for visual output).

Work through these steps in order, and you should get your video playing with detection markers in no time!

内容的提问来源于stack exchange，提问作者Frank