python3从网络摄像机解析mjpeg http流的示例

前言

网络摄像头的视频流解析直接使用通过http的Mjpeg是具有边界帧信息的multipart / x-mixed-replace，而jpeg数据只是以二进制形式发送。因此，实际上不需要关心HTTP协议标头。所有jpeg帧均以marker开头，0xff 0xd8并以结尾0xff 0xd9。因此，上面的代码从http流中提取了此类帧，并将其一一解码。像下面

...(http)
0xff 0xd8   --|
[jpeg data]   |--this part is extracted and decoded
0xff 0xd9   --|
...(http)
0xff 0xd8   --|
[jpeg data]   |--this part is extracted and decoded
0xff 0xd9   --|
...(http)

如果图像的获取是从tcp网络中传输到本地进行解析需要对bytes类型数据进行解码

在使用OpenCV直接调用网络摄像头时可能会出现

Cam not found

这时候就需要下面这种办法

代码： 
帧解析

import cv2
cap = cv2.VideoCapture(\'http://localhost:8080/frame.mjpg\')
 
while True:
 ret, frame = cap.read()
 print(frame)
 if ret == True:
  cv2.imshow(\'Video\', frame)
 
  if cv2.waitKey(1) == 27:
   exit(0)

视频流解析

import cv2
import requests
import numpy as np
 
r = requests.get(\'http://192.168.1.xx/mjpeg.cgi\', auth=(\'user\', \'password\'), stream=True)
if(r.status_code == 200):
  bytes = bytes()
  for chunk in r.iter_content(chunk_size=1024):
    bytes += chunk
    a = bytes.find(b\'\\xff\\xd8\')
    b = bytes.find(b\'\\xff\\xd9\')
    if a != -1 and b != -1:
      jpg = bytes[a:b+2]
      bytes = bytes[b+2:]
      i = cv2.imdecode(np.fromstring(jpg, dtype=np.uint8), cv2.IMREAD_COLOR)
      cv2.imshow(\'i\', i)
      if cv2.waitKey(1) == 27:
        exit(0)
else:
  print(\"Received unexpected status code {}\".format(r.status_code))

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