Reading Video Files

import cv2
import time

def process_video_file(video_path, process_fn=None, max_frames=None):
    """
    Read and process a video file frame by frame.
    process_fn: optional function to apply to each frame
    """
    cap = cv2.VideoCapture(video_path)
    if not cap.isOpened():
        print(f"Error: Could not open '{video_path}'")
        return

    fps = cap.get(cv2.CAP_PROP_FPS)
    total_frames = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
    print(f"Processing: {video_path} ({total_frames} frames at {fps:.1f} FPS)")

    frame_count = 0
    start_time = time.time()

    while True:
        ret, frame = cap.read()

        if not ret:
            print("End of video reached")
            break

        if max_frames and frame_count >= max_frames:
            print(f"Reached max_frames limit ({max_frames})")
            break

        # Apply processing function if provided
        if process_fn:
            frame = process_fn(frame)

        frame_count += 1

        # Log progress every 100 frames
        if frame_count % 100 == 0:
            elapsed = time.time() - start_time
            proc_fps = frame_count / elapsed
            pct = frame_count / total_frames * 100
            print(f"  Frame {frame_count}/{total_frames} ({pct:.1f}%) — {proc_fps:.1f} FPS")

    cap.release()
    elapsed = time.time() - start_time
    print(f"Done: {frame_count} frames in {elapsed:.1f}s ({frame_count/elapsed:.1f} FPS)")

# Example: convert video to grayscale
def make_grayscale(frame):
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    return cv2.cvtColor(gray, cv2.COLOR_GRAY2BGR)  # Convert back for saving

process_video_file("input.mp4", process_fn=make_grayscale, max_frames=300)