How to crop a video exactly the way I want on PC?

When you learn how to crop the length of a video with OpenCV, the process involves two main steps: calculating the duration and then selectively writing frames to a new file.

First, you need to get the video's properties. OpenCV can read the total number of frames and the frames per second (fps) to calculate the video's duration.

python

import cv2

cap = cv2.Video Capture("your_ video. mp4")

frames = int(cap. get(cv2. CAP PROP FRAME_COUNT))

fps = cap. get(cv2.CAP_PROP_FPS)

duration = frames / fps # Duration in seconds

print(f"Duration: {duration} seconds")

The technique for how to crop the length of a video is to skip frames. For example, to create a video that is half the length, you can write only every other frame to the output file . The cap. grab() method reads and discards a frame, advancing the video position.

python

# ... (code to get video properties and set up VideoWriter)

# To create a video half the length, write every other frame

while True:

ret, frame = cap. read()

if not ret:

break

cap. grab() # Skip the next frame

out.write (frame) # Write the current frame

While it's possible, using OpenCV alone for trimming has significant drawbacks.

• Re-encoding is Required: OpenCV can't perform lossless trimming. It must decode and re-encode every frame it writes out . This means the output video will have quality loss and the process is much slower than using a tool like ff mpeg.
• Complexity: For a simple "cut from 1:00 to 2:00," you must write code to calculate the starting frame index and then loop to read and write only the frames within that range . This is much more involved than using a dedicated tool.
• Frame Accuracy: When you use OpenCV to crop the length of a video, your cut points are limited by the video's frame rate. You can only cut at specific frame numbers, not at exact, arbitrary timestamps like 1:23.45 .