A practical guide to implementing a real-time object discovery system with python

Vincent van Gogh (1853–1890), Paris, May-July 1887 (source)
You can create a video stream to feed your application using OpenCV. (source)

Reads on YouTube

import cv2 # opencv2 package for python.
import pafy # pafy allows us to read videos from youtube.
URL = "https://www.youtube.com/watch?v=dQw4w9WgXcQ" #URL to parse
play = pafy.new(self._URL).streams[-1] #'-1' means read the lowest quality of video.
assert play is not None # we want to make sure their is a input to read.
stream = cv2.VideoCapture(play.url) #create a opencv video stream.

Reading from WebCam

import cv2stream = cv2.VideoCapture(0) # 0 means read from local camera.

Reading the IP camera

import cv2camera_ip = "rtsp://username:password@IP/port"
stream = cv2.VideoCapture(camera_ip)
According to the Yolov5 paper, it is the fastest model on the market at the moment. (source)
from torch import hub # Hub contains other models like FasterRCNNmodel = torch.hub.load( 
The function below identifies the device which is availabe to make the prediction and uses it to load and infer the frame. Once it has results it will extract the labels and cordinates(Along with scores) for each object detected in the frame.
def score_frame(frame, model):
device = 'cuda' if torch.cuda.is_available() else 'cpu'
frame = [torch.tensor(frame)]
results = self.model(frame)
labels = results.xyxyn[0][:, -1].numpy()
cord = results.xyxyn[0][:, :-1].numpy()
return labels, cord
The function below takes the results and the frame as input and plots boxes over all the objects which have a score higer than our threshold.
def plot_boxes(self, results, frame):
labels, cord = results
n = len(labels)
x_shape, y_shape = frame.shape[1], frame.shape[0]
for i in range(n):
row = cord[i]
# If score is less than 0.2 we avoid making a prediction.
if row[4] < 0.2:
x1 = int(row[0]*x_shape)
y1 = int(row[1]*y_shape)
x2 = int(row[2]*x_shape)
y2 = int(row[3]*y_shape)
bgr = (0, 255, 0) # color of the box
classes = self.model.names # Get the name of label index
label_font = cv2.FONT_HERSHEY_SIMPLEX #Font for the label.
(x1, y1), (x2, y2),
bgr, 2) #Plot the boxes
(x1, y1),
label_font, 0.9, bgr, 2) #Put a label over box.
return frame
You can try to get different colors for different items. (Image by author)
The Function below oracestrates the entire operation and performs the real-time parsing for video stream.
def __call__(self):
player = self.get_video_stream() #Get your video stream.
assert player.isOpened() # Make sure that their is a stream.
#Below code creates a new video writer object to write our
#output stream.
x_shape = int(player.get(cv2.CAP_PROP_FRAME_WIDTH))
y_shape = int(player.get(cv2.CAP_PROP_FRAME_HEIGHT))
four_cc = cv2.VideoWriter_fourcc(*"MJPG") #Using MJPEG codex
out = cv2.VideoWriter(out_file, four_cc, 20,
(x_shape, y_shape))
ret, frame = player.read() # Read the first frame.
while rect: # Run until stream is out of frames
start_time = time() # We would like to measure the FPS.
results = self.score_frame(frame) # Score the Frame
frame = self.plot_boxes(results, frame) # Plot the boxes.
end_time = time()
fps = 1/np.round(end_time - start_time, 3) #Measure the FPS.
print(f"Frames Per Second : {fps}")
out.write(frame) # Write the frame onto the output.
ret, frame = player.read() # Read next frame.
60 FPS output stream from processed video in real time. (Image by author)

If you liked the guide.


Please enter your comment!
Please enter your name here