videocaptureasync.py

# https://github.com/gilbertfrancois/video-capture-async

import threading
import cv2
import time


WARMUP_TIMEOUT = 10.0


class VideoCaptureAsync:
    def __init__(self, src=0, width=640, height=480):
        self.src = src

        self.cap = cv2.VideoCapture(self.src)
        if not self.cap.isOpened():
            raise RuntimeError("Cannot open camera. Try to choose other CAMID in './scripts/settings.sh'")
        
        self.cap.set(cv2.CAP_PROP_FRAME_WIDTH, width)
        self.cap.set(cv2.CAP_PROP_FRAME_HEIGHT, height)
        self.grabbed, self.frame = self.cap.read()
        self.started = False
        self.read_lock = threading.Lock()

    def set(self, var1, var2):
        self.cap.set(var1, var2)

    def isOpened(self):
        return self.cap.isOpened()

    def start(self):
        if self.started:
            print('[!] Asynchronous video capturing has already been started.')
            return None
        self.started = True
        self.thread = threading.Thread(target=self.update, args=(), daemon=True)
        self.thread.start()

        # (warmup) wait for the first successfully grabbed frame 
        warmup_start_time = time.time()
        while not self.grabbed:
            warmup_elapsed_time = (time.time() - warmup_start_time)
            if warmup_elapsed_time > WARMUP_TIMEOUT:
                raise RuntimeError(f"Failed to succesfully grab frame from the camera (timeout={WARMUP_TIMEOUT}s). Try to restart.")

            time.sleep(0.5)
    
        return self

    def update(self):
        while self.started:
            grabbed, frame = self.cap.read()
            with self.read_lock:
                self.grabbed = grabbed
                self.frame = frame

    def read(self):
        with self.read_lock:
            frame = self.frame.copy()
            grabbed = self.grabbed
        return grabbed, frame

    def stop(self):
        self.started = False
        self.thread.join()

    def __exit__(self, exec_type, exc_value, traceback):
        self.cap.release()