Video writing in Computer Vision - ML Experiment: Train & Evaluate

Experiment - Video writing

Problem:You want to save a sequence of images as a video file using OpenCV in Python.

Current Metrics:The current code writes a video but the output video is corrupted or does not play properly.

Issue:The video writer parameters (codec, frame size, fps) are not set correctly, causing the video file to be unreadable.

Your Task

Fix the video writing code so that the saved video plays correctly with the expected frame size and frame rate.

Use OpenCV (cv2) for video writing.

Keep the frame size and fps consistent with the input images.

Do not change the source images.

Hint 1

Hint 2

Hint 3

Solution

Computer Vision

import cv2
import numpy as np

# Create dummy images (e.g., 100 frames of 640x480 with random colors)
frame_width, frame_height = 640, 480
num_frames = 100
frames = [np.random.randint(0, 256, (frame_height, frame_width, 3), dtype=np.uint8) for _ in range(num_frames)]

# Define video writer parameters
fourcc = cv2.VideoWriter_fourcc(*'mp4v')  # Codec for mp4
fps = 20
out = cv2.VideoWriter('output_video.mp4', fourcc, fps, (frame_width, frame_height))

for frame in frames:
    out.write(frame)  # Write each frame

out.release()  # Release the video writer
print('Video writing completed successfully.')

Set the codec to 'mp4v' which is widely supported for mp4 files.

Ensured the frame size matches exactly the size of the input images (640x480).

Set fps to 20 for smooth playback.

Used a proper VideoWriter object with correct parameters.

Results Interpretation

Before: Video file was corrupted or would not play due to incorrect codec or frame size.
After: Video plays smoothly with correct resolution and frame rate.

Setting the correct codec, frame size, and fps is essential for successful video writing. Mismatched parameters cause corrupted or unplayable video files.

Bonus Experiment

Try writing the video in grayscale instead of color.

💡 Hint

Convert each frame to grayscale using cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY) and adjust the VideoWriter parameters accordingly (set isColor=False).