Extract images using opencv and python or moviepy

Question

I have a video (.mp4) that has ~8000 frames. I have a csv that tells me the time that I need to grab each frame at in the video, and the number of frames to grab. number_of_frames in video = 8000 times is an array like [0.004, 0.005, ... 732s] The last time in the data given is at 732s. Therefore the FPS = 8000 / 732 = ~10

I want to be able to extract the image frames from the video at those specific times. Then write those image paths to a .csv file.

I tried multiple approaches: First approach(openCV):

with open('./data/driving.csv', 'w') as csvfile:
fieldnames = ['image_path', 'time', 'speed']
writer = csv.DictWriter(csvfile, fieldnames = fieldnames)
writer.writeheader()
vidcap = cv2.VideoCapture('./data/drive.mp4')
for idx, item in enumerate(ground_truth):
    # set video capture to specific time frame
    # multiply time by 1000 to convert to milliseconds
    vidcap.set(cv2.CAP_PROP_POS_MSEC, item[0] * 1000)
    # read in the image
    success, image = vidcap.read()
    if success:
        image_path = os.path.join('./data/IMG/', str(item[0]) + 
     '.jpg')
        # save image to IMG folder
        cv2.imwrite(image_path, image)
        # write row to driving.csv
        writer.writerow({'image_path': image_path, 
                 'time':item[0],
                 'speed':item[1],
                })

This approach however, did not give me the total number of frames desired. It just gave me the number of frames that would correspond to a video at FPS = 25. I believe my FPS = 8000 / 732s = 10.928s.

I then tried using moviepy to capture each image in a similar style:

from moviepy.editor import VideoFileClip
clip1 = VideoFileClip('./data/drive.mp4')
with open('./data/driving.csv', 'w') as csvfile:
    fieldnames = ['image_path', 'time', 'speed']
    writer = csv.DictWriter(csvfile, fieldnames = fieldnames)
    writer.writeheader()

    # Path to raw image folder
    abs_path_to_IMG = os.path.join('./data/IMG/')
    for idx, item in enumerate(ground_truth):
      image_path = os.path.join('./data/IMG/', str(item[0]) + '.jpg')
      clip1.save_frame(image_path, t = item[0])
      # write row to driving.csv
      writer.writerow({'image_path': image_path, 
             'time':item[0],
             'speed':item[1],
            })

However this approach did not work either, for some reason I am capturing the last frame in the video hundreds of times.

Answer 1

This code works OK to extract frames at different times:

import os
from moviepy.editor import *

def extract_frames(movie, times, imgdir):
    clip = VideoFileClip(movie)
    for t in times:
        imgpath = os.path.join(imgdir, '{}.png'.format(t))
        clip.save_frame(imgpath, t)

movie = 'movie.mp4'
imgdir = 'frames'
times = 0.1, 0.63, 0.947, 1.2, 3.8, 6.7

extract_frames(movie, times, imgdir)

What's the content of your ground_truth variable?