我在RasbpberryPI 3上运行了简单的python脚本。这个脚本可以打开视频设备并使用MJPEG将数据流(800x600)传输到HTTP端点。当我回忆这个流时,我的一个rasbpberrypi核心可以100%运行。可以用多线程运行OpenCV吗?
这是我的代码
import cv2
from BaseHTTPServer import BaseHTTPRequestHandler, HTTPServer
import time
import argparse
import socket as Socket
camera = None
def setUpCameraCV():
global camera
camera = cv2.VideoCapture(0)
class mjpgServer(BaseHTTPRequestHandler):
ip = None
hostname = None
def do_GET(self):
print('connection from:', self.address_string())
if self.ip is None or self.hostname is None:
self.ip, _ = 0.0.0.0
self.hostname = Socket.gethostname()
if self.path == '/mjpg':
self.send_response(200)
self.send_header('Cache-Control', 'no-cache')
self.send_header('Pragma', 'no-cache')
self.send_header('Connection', 'close')
self.send_header(
'Content-type',
'multipart/x-mixed-replace; boundary=mjpegstream'
)
self.end_headers()
while True:
if camera:
ret, img = camera.read()
else:
raise Exception('Error, camera not setup')
if not ret:
print('no image from camera')
time.sleep(1)
continue
ret, jpg = cv2.imencode('.jpg', img)
self.end_headers()
self.wfile.write('--mjpegstream')
self.end_headers()
self.send_header('Content-type', 'image/jpeg')
self.send_header('Content-length', str(jpg.size))
self.end_headers()
self.wfile.write(jpg.tostring())
def main():
try:
setUpCameraCV()
mjpgServer.ip = 0.0.0.0
mjpgServer.hostname = Socket.gethostname()
server = HTTPServer((ipv4, args['port']), mjpgServer)
print("server started on {}:{}".format(Socket.gethostname(), args['port']))
server.serve_forever()
except KeyboardInterrupt:
print('KeyboardInterrupt')
server.socket.close()
if __name__ == '__main__':
main()
另一个问题,如何在客户端(接收器)获取每个帧的时间戳?
使用线程来处理I / O繁重操作(例如从网络摄像头读取帧)是一种经典的编程模型。由于使用cv2.VideoCapture().read()
访问网络摄像头/摄像头是一种阻止操作,我们的主程序会停止,直到从摄像头设备读取帧并返回到我们的脚本。本质上,我们的想法是生成另一个线程来处理并行抓取帧而不是依赖单个线程(我们的“主”线程)按顺序抓取帧。这将允许从I / O线程连续读取帧,而我们的根线程处理当前帧。一旦根线程完成处理它的帧,它只需要从I / O线程中获取当前帧,而不必等待阻塞I / O操作。
因此,我们可以通过创建一个新线程来提高性能,当我们的主线程处理当前帧时,该线程除了轮询新帧之外什么都不做。
from threading import Thread
import cv2, time
class VideoStreamWidget(object):
def __init__(self, src=0):
self.capture = cv2.VideoCapture(src)
# 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()
time.sleep(.01)
def show_frame(self):
# Display frames in main program
cv2.imshow('frame', self.frame)
key = cv2.waitKey(1)
if key == ord('q'):
self.capture.release()
cv2.destroyAllWindows()
exit(1)
if __name__ == '__main__':
video_stream_widget = VideoStreamWidget()
while True:
try:
video_stream_widget.show_frame()
except AttributeError:
pass