Saving key event video clips with OpenCV

Saving key event video clips with OpenCV

If you're trying to save short video clips when a certain key event occurs, you can use OpenCV to accomplish this. The basic idea is to continuously capture video frames and then, upon detecting a key event, save the last few seconds as a video clip.

Here's a simple example using OpenCV to demonstrate this concept:

  1. Continuously capture video.
  2. Store frames in a buffer.
  3. When a key event occurs (let's use the 's' key as an example), save the buffered frames as a video clip.
import cv2 import numpy as np # Open the video capture cap = cv2.VideoCapture(0) # Use 0 for default camera # Define the codec and create VideoWriter object fourcc = cv2.VideoWriter_fourcc(*'XVID') out = cv2.VideoWriter('output.avi', fourcc, 20.0, (int(cap.get(3)), int(cap.get(4)))) # Number of frames to store in buffer (e.g., 100 frames at 20 fps will give 5 seconds of video) buffer_size = 100 frame_buffer = [] while cap.isOpened(): ret, frame = cap.read() if ret: # Show the current frame cv2.imshow('Video', frame) # Add the frame to the buffer and maintain buffer size frame_buffer.append(frame) if len(frame_buffer) > buffer_size: frame_buffer.pop(0) key = cv2.waitKey(1) # If 's' key is pressed, save the buffered frames as a video clip if key == ord('s'): for buffered_frame in frame_buffer: out.write(buffered_frame) print("Saved video clip!") # If 'q' key is pressed, exit the loop elif key == ord('q'): break else: break cap.release() out.release() cv2.destroyAllWindows()

In this example:

  • We continuously capture frames from the default camera.
  • The captured frames are stored in frame_buffer. We maintain a fixed buffer size to store the last few seconds of video.
  • When the 's' key is pressed, the frames in the buffer are written to the video file, effectively saving a video clip of the last few seconds.
  • The 'q' key can be pressed to quit the capture.

You can adjust the buffer size and frame rate to save longer or shorter video clips. Also, you can implement other mechanisms for the key event trigger (like motion detection) depending on your requirements.

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