How to create array of frames from an mp4 with opencv for python

Question

I am attempting to use opencv_python to break an mp4 file down into it's frames so I can later open them with pillow, or at least be able to use the images to run my own methods on them.

I understand that the following snippet of code gets a frame from a live video or a recorded video.

    import cv2
    cap = cv2.VideoCapture("myfile.mp4")
    boolean, frame = cap.read()

What exactly does the read function return and how can I create an array of images which I can modify.

Answer 1

adapted from How to process images of a video, frame by frame in video streaming using Opencv python . Untested. However, the frames are read into a numpy array and and append to a list that is converted to a numpy array when the all the frames are read in.

import cv2
import numpy as np


images = []

cap = cv2.VideoCapture("./out.mp4")
while not cap.isOpened():
    cap = cv2.VideoCapture("./out.mp4")
    cv2.waitKey(1000)
    print "Wait for the header"

pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)
while True:
    boolen, frame = cap.read() # get the frame
    if flag:
        # The frame is ready and already captured
        # cv2.imshow('video', frame)

        # store the current frame in as a numpy array
        np_frame = cv2.imread('video', frame)
        images.append(np_frame)

        pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)
    else:
        # The next frame is not ready, so we try to read it again
        cap.set(cv2.cv.CV_CAP_PROP_POS_FRAMES, pos_frame-1)
        print "frame is not ready"
        # It is better to wait for a while for the next frame to be ready
        cv2.waitKey(1000)

    if cv2.waitKey(10) == 27:
        break
    if cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES) == cap.get(cv2.cv.CV_CAP_PROP_FRAME_COUNT):
        # If the number of captured frames is equal to the total number of frames,
        # we stop
        break

all_frames = np.array(images)