Python opencv subprocess write return broken pipe

Python
1

I want to read an rtsp video source, add overlay text and push it to the RTMP endpoint.I am using Videocapture to read the video source and python subprocess to write the frames back to RTMP endpoint. I referred this FFmpeg stream video to rtmp from frames OpenCV python - Stack Overflow

import sys
    import subprocess
    
    import cv2
    import ffmpeg
    rtmp_url = "rtmp://127.0.0.1:1935/live/test"
    
    path = 0
    cap = cv2.VideoCapture("rtsp://10.0.1.7/media.sdp")
    
    # gather video info to ffmpeg
    fps = int(cap.get(cv2.CAP_PROP_FPS))
    width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
    height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
    
    
    
    command = ['ffmpeg', '-i', '-', "-c", "copy", '-f', 'flv', rtmp_url]
    p = subprocess.Popen(command, stdin=subprocess.PIPE, stderr=subprocess.PIPE, stdout=subprocess.PIPE)
    
    font = cv2.FONT_HERSHEY_SIMPLEX
    while cap.isOpened():
    
        ret, frame = cap.read()
        cv2.putText(frame, 'TEXT ON VIDEO', (50, 50), font, 1, (0, 255, 255), 2, cv2.LINE_4)
        cv2.imshow('video', frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    
        if not ret:
            print("frame read failed")
            break
    
        try:
            p.stdin.write(frame.tobytes())
        except Exception as e:
            print (e)
    
    
    cap.release()
    p.stdin.close()
    p.stderr.close()
    p.wait()

The python script returns “[Errno 32] Broken pipe”. Running the ffmpeg command in the terminal works fine.

ffmpeg -i rtsp://10.0.1.7/media.sdp -c copy -f flv
rtmp://127.0.0.1:1935/live/test

The above command works fine, and I can push the input stream to RTMP endpoint. But I can’t write processed frame to subprocess which has ffmpeg running.

Please let me know if I miss anything.

2

btw,

this has to go directly after cap.read()

3

and you didn’t tell the ffmpeg subprocess what format of data you’d be sending it.

browse the videoio tag. this problem has been discussed before…