OpenCV Python, reading video from named pipe

2024/4/15 1:18:29

I am trying to achieve results as shown on the video (Method 3 using netcat)

The point is to stream video from raspberry pi to ubuntu PC and process it using openCV and python.

I use command

raspivid -vf -n -w 640 -h 480 -o - -t 0 -b 2000000 | nc 5777

to stream the video to my PC and then on the PC I created name pipe 'fifo' and redirected the output

 nc -l -p 5777 -v > fifo

then i am trying to read the pipe and display the result in the python script

import cv2
import sysvideo_capture = cv2.VideoCapture(r'fifo')
video_capture.set(cv2.CAP_PROP_FRAME_WIDTH, 640);
video_capture.set(cv2.CAP_PROP_FRAME_HEIGHT, 480);while True:# Capture frame-by-frameret, frame = ret == False:passcv2.imshow('Video', frame)if cv2.waitKey(1) & 0xFF == ord('q'):break# When everything is done, release the capture

However I just end up with an error

[mp3 @ 0x18b2940] Header missing this error is produced by the command video_capture = cv2.VideoCapture(r'fifo')

When I redirect the output of netcat on PC to a file and then reads it in python the video works, however it is speed up by 10 times approximately.

I know the problem is with the python script, because the nc transmission works (to a file) but I am unable to find any clues.

How can I achieve the results as shown on the provided video (method 3) ?


I too wanted to achieve the same result in that video. Initially I tried similar approach as yours, but it seems cv2.VideoCapture() fails to read from named pipes, some more pre-processing is required.

ffmpeg is the way to go ! You can install and compile ffmpeg by following the instructions given in this link:

Once it is installed, you can change your code like so:

import cv2
import subprocess as sp
import numpyFFMPEG_BIN = "ffmpeg"
command = [ FFMPEG_BIN,'-i', 'fifo',             # fifo is the named pipe'-pix_fmt', 'bgr24',      # opencv requires bgr24 pixel format.'-vcodec', 'rawvideo','-an','-sn',              # we want to disable audio processing (there is no audio)'-f', 'image2pipe', '-']    
pipe = sp.Popen(command, stdout = sp.PIPE, bufsize=10**8)while True:# Capture frame-by-frameraw_image =*480*3)# transform the byte read into a numpy arrayimage =  numpy.fromstring(raw_image, dtype='uint8')image = image.reshape((480,640,3))          # Notice how height is specified first and then widthif image is not None:cv2.imshow('Video', image)if cv2.waitKey(1) & 0xFF == ord('q'):breakpipe.stdout.flush()cv2.destroyAllWindows()

No need to change any other thing on the raspberry pi side script.

This worked like a charm for me. The video lag was negligible. Hope it helps.

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