如何使用OpenCV从python中的NamedTempFile中读取视频

Question

我想从视频中读取帧，但在提取帧后视频无用。所以我决定使用TempFile模块。但是我使用cv2.VideoCapture(NamedTempFile.name)得到的帧始终是黑色的。我想知道这是否是正确的做法。如果没有，有没有更好的办法？ 我在下面附上了我的代码的视频捕获部分。
另外我怀疑get_temp_video函数可能是错误的。

---

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

我猜问题是你的函数upload_to_some_where，因为其余代码为我工作得很好。出于测试目的，我稍微修改了您的代码：

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')