Displaying RTSP stream with OpenCV and gstreamer

Question

I have purchased an IP camera which I am trying to connect to using RTSP. The RTSP connection URL is rtsp://admin:@192.168.0.27/channel=1&stream=0.554. I am using OpenCV to open and display the stream:

#include <opencv2/opencv.hpp>

int main() {
   cv::VideoCapture cap;
   if (!cap.open("rtsp://admin:@192.168.0.27/channel=1&stream=0.554")) {
        std::cout << "Unable to open video capture\n";
        return -1;
    }

    while(true) {
        cv::Mat frame;

        auto ret = cap.grab();
        cap >> frame;

        if (frame.empty()) {
            break; // End of video stream
        }

        cv::resize(frame, frame, cv::Size(640, 480));

        // Do other stuff here with frame

        cv::imshow("frame", frame);

        if (cv::waitKey(10) == 27) {
            break; // stop capturing by pressing ESC
        }
    }

    return 0;
}

When I run the program, it will connect successfully and display a few frames, but then will start to lag badly and usually hang and output some error like this before crashing:

[h264 @ 0x558ae8e601a0] error while decoding MB 93 40, bytestream -11

I am not sure why I am having issues displaying the stream consistently. Additionally, when it is able to display the stream, I find that it is quickly become out of sync (note I am doing some heavy processing on the frame which takes quite a lot of time). As in, it is not displaying the real time frame, but there is a growing lag.

How can I also ensure to use the "latest" frame, and discard all the other ones which may have accumulated in some buffer. Also, any ideas why it is crashing and how I can improve the streaming?

I was able to find this SO post which deals with getting the latest frame using gstreamer. When I modify my video capture string to utilize gstreamer, it works a bit better.

Here is the modified connection string: "rtspsrc location=rtsp://admin:@192.168.0.27/channel=1&stream=0.554 ! decodebin ! videoconvert ! appsink max-buffers=1 drop=true"

I have no experience with gstreamer so I am not sure what it is doing, but it seems to improve things. However, once it a while, it will all go grey and only display the pixels when there is movement, as shown in the following images. With my experince with codecs, I believe the reference frame is missing, but I am not really sure. Any ideas on how to fix this? If I am not using the correct gstreamer parameters, please make a suggestion as to what I should be using for fast streaming (always using the latest frame). As I mentioned, I have minimal experience with gstreamer. Thanks for the help!

Answer 1

This may be due to packet loss of the network transmission. You can give it a try to modify the URL to use the rtspt:// protocol. This will try to establish a TCP transmission which should prevent packet loss on your receiving side.

Answer 2

The best approach is to use threads to read frames continuously and assign them on an attribute of a class. In this way if some thread encounters the packet loss, the other thread buddies compensate for it.

check this out, I hope it helps:

from threading import Thread
import cv2

class RTSPVideoWriterObject(object):
    def __init__(self, src=0):
        # Create a VideoCapture object
        self.capture = cv2.VideoCapture(src)
        self.status, self.frame = None, None

        # Default resolutions of the frame are obtained (system dependent)
        self.frame_width = int(self.capture.get(3))
        self.frame_height = int(self.capture.get(4))

        # Set up codec and output video settings
        self.codec = cv2.VideoWriter_fourcc(*'MJPG')
        self.output_video = cv2.VideoWriter('output.avi', self.codec, 30, (self.frame_width, self.frame_height))

        # Start the thread to read frames from the video stream
        self.thread = Thread(target=self.update, args=())
        self.thread.daemon = True
        self.thread.start()

    def update(self):
        # Read the next frame from the stream in a different thread
        while True:
            if self.capture.isOpened():
                (self.status, self.frame) = self.capture.read()

    def show_frame(self):
        # Display frames in main program
        # if self.status:
        #     cv2.imshow('frame', self.frame)

        # Press Q on keyboard to stop recording
        key = cv2.waitKey(1)
        if key == ord('q'):
            self.capture.release()
            self.output_video.release()
            cv2.destroyAllWindows()
            exit(1)

    def save_frame(self):
        # Save obtained frame into video output file
        self.output_video.write(self.frame)


if __name__ == '__main__':
    rtsp_link = "rtsp://admin:@192.168.0.27/channel=1&stream=0.554"
    video_stream_widget = RTSPVideoWriterObject(rtsp_stream_link)
    while True:
        try:
            video_stream_widget.show_frame()
            video_stream_widget.save_frame()
        except AttributeError:
            pass