Quickly extract N keyframes from a video (requires python2 and opencv)

keyframes.py

from __future__ import division
import sys
import cv2
import contextlib


def main(num_keyframes, filepath):
    print("Extracting {} keyframes from '{}'...".format(num_keyframes, filepath))
    
    with video_file(filepath) as video:
        for title, keyframe in get_keyframes(video, num_keyframes):
            cv2.imwrite(title, keyframe)

    print("Done.")


@contextlib.contextmanager
def video_file(path):
    v = cv2.VideoCapture(path)
    yield v
    v.release()


def get_keyframes(video, num_keyframes):
    num_frames = int(video.get(cv2.cv.CV_CAP_PROP_FRAME_COUNT))

    for i in range(num_keyframes):
        title = "{}.png".format(i)
        keyframe = get_keyframe(video, num_frames, num_keyframes, i)
        yield title, keyframe


def get_keyframe(video, num_frames, num_keyframes, index):
    percentage = (index + 1)/(num_keyframes + 2)
    frame_index = int(percentage * num_frames)

    print("Extracting keyframe {}/{} (frame {})...".format(index + 1, num_keyframes, frame_index))

    video.set(cv2.cv.CV_CAP_PROP_POS_FRAMES, frame_index)
    return video.read()[1]


if __name__ == "__main__":
    if len(sys.argv) == 3:
        main(int(sys.argv[2]), sys.argv[1])
    else:
        print("Please specify the arguments: <video_file> <number_of_keyframes>")
        sys.exit(1)