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• Efficiently Fetching the Latest Frame from a Live Stream using OpenCV in Python

  10 juillet 2023, par Nicolantonio De Bari

  Problem :

  


  I have a FastAPI server that connects to a live video feed using cv2.VideoCapture. The server then uses OpenCV to process the frames for object detection and sends the results to a WebSocket. Here's the relevant part of my code :

  


  class VideoProcessor:
    # ...

    def update_frame(self, url):
        logger.info("update_frame STARTED")
        cap = cv2.VideoCapture(url)
        while self.capture_flag:
            ret, frame = cap.read()
            if ret:
                frame = cv2.resize(frame, (1280, 720))
                self.current_frame = frame
            else:
                logger.warning("Failed to read frame, retrying connection...")
                cap.release()
                time.sleep(1)
                cap = cv2.VideoCapture(url)

    async def start_model(self, url, websocket: WebSocket):
        # ...
        threading.Thread(target=self.update_frame, args=(url,), daemon=True).start()
        while self.capture_flag:
            if self.current_frame is not None:
                frame = cv2.resize(self.current_frame, (1280, 720))
                bbx = await self.process_image(frame)
                await websocket.send_text(json.dumps(bbx))
                await asyncio.sleep(0.1)


  


  Currently, I'm using a separate thread (update_frame) to continuously fetch frames from the live feed and keep the most recent one in self.current_frame.

  


  The issue with this method is that it uses multi-threading and continuously reads frames in the background, which is quite CPU-intensive. The cv2.VideoCapture.read() function fetches the oldest frame in the buffer, and OpenCV does not provide a direct way to fetch the latest frame.

  


  Goal

  


  I want to optimize this process by eliminating the need for a separate thread and fetching the latest frame directly when I need it. I want to ensure that each time I process a frame in start_model, I'm processing the most recent frame from the live feed.

  


  I have considered a method of continuously calling cap.read() in a tight loop to "clear" the buffer, but I understand that this is inefficient and can lead to high CPU usage.

  


  Attempt :

  


  What I then tried to do is use ffmpeg & subprocess to get the latest frame, but I dont seem to understand how to get the latest frame then.

  


  async def start_model(self, url, websocket: WebSocket):
    try:
        logger.info("Model Started")
        self.capture_flag = True

        command = ["ffmpeg", "-i", url, "-f", "image2pipe", "-pix_fmt", "bgr24", "-vcodec", "rawvideo", "-"]
        pipe = subprocess.Popen(command, stdout=subprocess.PIPE, bufsize=10**8)

        while self.capture_flag:
            raw_image = pipe.stdout.read(1280*720*3)  # read 720p frame (BGR)
            if raw_image == b'':
                logger.warning("Failed to read frame, retrying connection...")
                await asyncio.sleep(1) # delay for 1 second before retrying
                continue
            
            frame = np.fromstring(raw_image, dtype='uint8')
            frame = frame.reshape((720, 1280, 3))
            if frame is not None:
                self.current_frame = frame
                frame = cv2.resize(self.current_frame, (1280, 720))
                bbx = await self.process_image(frame)
                await websocket.send_text(json.dumps(bbx))
                await asyncio.sleep(0.1)
                
        pipe.terminate()

    except WebSocketDisconnect:
        logger.info("WebSocket disconnected during model operation")
        self.capture_flag = False  # Ensure to stop the model operation when the WebSocket disconnects


  


  Question

  


  Is there a more efficient way to fetch the latest frame from a live stream using OpenCV in Python ? Can I modify my current setup to get the newest frame without having to read all the frames in a separate thread ?
Or is there another library that I could use ?

  


  I know a similar question has been asked, but not related to video streaming.

  


• How can i get the live stream from my gopro hero 5 on c# wpf

  8 avril 2022, par Kanoto

  I'm trying to livestream with my GoPro and showing it on wpf application.

  


  var inputArgs = "-framerate 20 -f rawvideo -pix_fmt rgb32 -video_size 1920x1080 -i udp://10.5.5.100:8554";
var outputArgs = "-vcodec libx264 -crf 23 -pix_fmt yuv420p -preset ultrafast -r 20 out.mp4";

var process = new Process
{
    StartInfo =
    {
        FileName = "ffmpeg.exe",
        Arguments = $"{inputArgs} {outputArgs}",
        UseShellExecute = false,
        CreateNoWindow = false,
        RedirectStandardInput = true
    }
};


  


  But I can't make it work, even using that command on cmd/powershell :

  


  ffplay -fflags nobuffer -f:v mpegts -probesize 8192 -i udp://10.5.5.100:8554 -f mpegts -vcodec copy udp://localhost:10000


  


  But for some reasons, when i try with the py script over there : https://github.com/KonradIT/GoProStream/blob/master/GoProStream.py
  
it works but I can't explain why, I copy/paste the same command but doesn't work.

  


• How to extract good quality frame in pixel format from live mpeg-ts stream ?

  2 février 2024, par Aven

  I use the command below to stream my ts file for my programe :

  


  ffmpeg -re -i independent_frame.ts -f mpegts udp://127.0.0.1:10002


  


  Below is the code of my programe, I'm trying to extract each frame in pixel format from the stream by using FFmpeg, but I found the quality is not good as it should be of the extracted frame ( I know OpenCV can do this, But I have other reason have to use FFmpeg ). I tried to put -qscale:v 2 in FFmpeg command, but it seems change nothing. Does anyone know how to enhance the frame quality in this case ? Thanks !

  


  stream = 'udp://127.0.0.1:10002'
H, W = 720, 1280

command = [ 'ffmpeg',
            '-i', stream ,
            '-pix_fmt', 'bgr24', # brg24 for matching OpenCV
            '-qscale:v', '2', 
            '-f', 'rawvideo',
            'pipe:' ]

# Execute FFmpeg as sub-process with stdout as a pipe
process = subprocess.Popen(command, stdout=subprocess.PIPE, bufsize=10**8)#10**8

# Load individual frames in a loop
nb_img = H*W*3

# Read decoded video frames from the PIPE until no more frames to read
num = 0
while True:
    # Read decoded video frame (in raw video format) from stdout process.
    buffer = process.stdout.read(W*H*3)

    # Break the loop if buffer length is not W*H*3 (when FFmpeg streaming ends).
    if len(buffer) != W*H*3:
        break

    img = np.frombuffer(buffer, np.uint8).reshape(H, W, 3)
    num +=1

    if num == 435:
        cv2.imwrite('435.png', img)
        cv2.imshow('img', img)  # Show the image for testing
        cv2.waitKey(0)
        cv2.destroyAllWindows()
        break

process.stdout.close()
process.wait()
cv2.destroyAllWindows()