opencv and multiprocessing read error [h264 @ 0x7fa02816f2c0] error while decoding MB 26 11, bytestream -7

Question

I read this thread and got the stream working using threading. opencv read error:[h264 @ 0x8f915e0] error while decoding MB 53 20, bytestream -7.

As suggested in the upvoted answer I use different functions for reading the stream and processing the frames as follows.

def Receive(stream, raw_frame_queue):
    print("start Receive")
    cap = cv2.VideoCapture(stream)
    while True:
        ret, frame = cap.read()
        if not ret:
            print("Not successfull")
            break
        raw_frame_queue.put(frame)
        time.sleep(0.25)
    cap.release()

def Prepare(raw_frame_queue):
    print("Start preparing")
    frame_buffer = deque([], 30)
    while True:
        if raw_frame_queue.empty():
            continue
        frame_buffer.append(raw_frame_queue.get())
        lots of other stuff

everything works as expected with threading:

import queue
import threading

raw_frame_queue = queue.Queue()

if __name__=='__main__':
    p1 = threading.Thread(target=Receive, args=((RTSP_URL, raw_frame_queue)))
    p2 = threading.Thread(target=Prepare, args=((raw_frame_queue),))
    p1.start()
    p2.start()

Using multiprocessing however the frames can't be decoded:

from multiprocessing import Process, Queue
raw_frame_queue = Queue()

if __name__=='__main__':
    p1 = Process(target=Receive, args=((RTSP_URL, raw_frame_queue)))
    p2 = Process(target=Prepare, args=((raw_frame_queue),))
    p1.start()
    p2.start()

The errormessage are something like [h264 @ 0x7fa02816f2c0] error while decoding MB 26 11, bytestream -7 for every single frame. Quick sidenote, "Not successfull" is never printed, so the frames can always be grabbed

Thank you for the provided links. They all are talking about threading however, which I got to work. The problem described however is in context of multiprocessing. — Tom S, May 04 '22 at 07:08

score 0 · Accepted Answer · answered Jul 01 '22 at 13:34

Still haven't got this to work directly, but since the Receive function is not very compute heavy. I ended up running it in a different thread and all other functions such as Prepare, which are all quite a bit more complex and CPU bounded in different processes. This keep parallelism at an sufficient level for my application.

opencv and multiprocessing read error [h264 @ 0x7fa02816f2c0] error while decoding MB 26 11, bytestream -7

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