Issue
I'm trying to send live video frame that I catch with my camera to a server and process them. I'm usig opencv for image processing and python for the language. Here is my code
client_cv.py
import cv2
import numpy as np
import socket
import sys
import pickle
cap=cv2.VideoCapture(0)
clientsocket=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
clientsocket.connect(('localhost',8089))
while True:
ret,frame=cap.read()
print sys.getsizeof(frame)
print frame
clientsocket.send(pickle.dumps(frame))
server_cv.py
import socket
import sys
import cv2
import pickle
import numpy as np
HOST=''
PORT=8089
s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
print 'Socket created'
s.bind((HOST,PORT))
print 'Socket bind complete'
s.listen(10)
print 'Socket now listening'
conn,addr=s.accept()
while True:
data=conn.recv(80)
print sys.getsizeof(data)
frame=pickle.loads(data)
print frame
cv2.imshow('frame',frame)
This code gives me end of file error, which is logical because the data always keep coming to the server and pickle doesn't know when to finish. My search on the internet made me use pickle but it doesn't work so far.
Note: I set conn.recv
to 80 because that's the number I get when I say print sys.getsizeof(frame)
.
Solution
Few things:
- use
sendall
instead ofsend
since you're not guaranteed everything will be sent in one go pickle
is ok for data serialization but you have to make a protocol of you own for the messages you exchange between the client and the server, this way you can know in advance the amount of data to read for unpickling (see below)- for
recv
you will get better performance if you receive big chunks, so replace 80 by 4096 or even more - beware of
sys.getsizeof
: it returns the size of the object in memory, which is not the same as the size (length) of the bytes to send over the network ; for a Python string the two values are not the same at all - be mindful of the size of the frame you are sending. Code below supports a frame up to 65535. Change "H" to "L" if you have a larger frame.
A protocol example:
client_cv.py
import cv2
import numpy as np
import socket
import sys
import pickle
import struct ### new code
cap=cv2.VideoCapture(0)
clientsocket=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
clientsocket.connect(('localhost',8089))
while True:
ret,frame=cap.read()
data = pickle.dumps(frame) ### new code
clientsocket.sendall(struct.pack("H", len(data))+data) ### new code
server_cv.py
import socket
import sys
import cv2
import pickle
import numpy as np
import struct ## new
HOST=''
PORT=8089
s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
print('Socket created')
s.bind((HOST,PORT))
print('Socket bind complete')
s.listen(10)
print('Socket now listening')
conn,addr=s.accept()
### new
data = ""
payload_size = struct.calcsize("H")
while True:
while len(data) < payload_size:
data += conn.recv(4096)
packed_msg_size = data[:payload_size]
data = data[payload_size:]
msg_size = struct.unpack("H", packed_msg_size)[0]
while len(data) < msg_size:
data += conn.recv(4096)
frame_data = data[:msg_size]
data = data[msg_size:]
###
frame=pickle.loads(frame_data)
print frame
cv2.imshow('frame',frame)
You can probably optimize all this a lot (less copying, using the buffer interface, etc) but at least you can get the idea.
Answered By - mguijarr
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