how do I use OpenCV to read video from a NamedTempFile in python

Question

I am trying to read frames from video but the video is useless after extracting frames. So I decide to use TempFile module. However the frame I use cv2.VideoCapture(NamedTempFile.name) to get is always black. I am wondering if this is the right way to do it. if not, is there a better way? I attach the video capture part of my code below.
Also I doubt that the get_temp_video function might be wrong.

---

def get_temp_video(url, temp_file):
    r = requests.get(url, stream=True)
    for chunk in r.iter_content(chunk_size=1024):
        if chunk:
            temp_file.write(chunk)
    return temp_file


def get_frame(video_url):
    named_temp_file = NamedTemporaryFile()
    named_temp_file = get_temp_video(video_url, named_temp_file)
    named_temp_file.seek(0)
    video = cv2.VideoCapture(named_temp_file.name)
    while video.isOpened():
        ret, frame = video.read()
        if ret:
            temp_file = TemporaryFile()
            np.save(temp_file, frame)
            temp_file.seek(0)
            upload_to_some_where(temp_file.read())
            temp_file.close()
        else:
            break
    video.release()
    named_temp_file.close()

Answer 1

I am guessing the problem is with your function upload_to_some_where , because the rest of the code works fine for me. For testing purposes I slightly modified your code:

def get_temp_video(url, temp_file):
    r = requests.get(url, stream=True)
    for chunk in r.iter_content(chunk_size=1024):
        if chunk:
            temp_file.write(chunk)
    return temp_file


def get_frame(video_url):
    named_temp_file = NamedTemporaryFile()
    named_temp_file = get_temp_video(video_url, named_temp_file)
    named_temp_file.seek(0)
    video = cv2.VideoCapture(named_temp_file.name)
    while video.isOpened():
        ret, frame = video.read()
        if ret:
          # For testing purpose
          cv2.imshow("frame", frame)
          if cv2.waitKey(25) == ord('q'):
            break
          ##############################
            # temp_file = TemporaryFile()
            # np.save(temp_file, frame)
            # temp_file.seek(0)
            # upload_to_some_where(temp_file.read())
            # temp_file.close()
        else:
            break
    video.release()
    named_temp_file.close()

if __name__=='__main__':

  get_frame('http://samples.mplayerhq.hu/MPEG-4/MPEG4%20by%20philips.mp4')