server.py

# RedisEdge realtime video analytics web server
import argparse
import cv2
import io
import numpy as np
import redis
from urllib.parse import urlparse
from PIL import Image, ImageDraw
from flask import Flask, render_template, Response

class RedisImageStream(object):
    def __init__(self, conn, args):
        self.conn = conn
        self.camera = args.camera
        self.boxes = args.boxes
        self.field = args.field.encode('utf-8')

    def get_last(self):
        ''' Gets latest from camera and model '''
        p = self.conn.pipeline()
        p.xrevrange(self.camera, count=1)  # Latest frame
        p.xrevrange(self.boxes, count=1)   # Latest boxes
        cmsg, bmsg = p.execute()
        if cmsg:
            last_id = cmsg[0][0].decode('utf-8')
            label = f'{self.camera}:{last_id}'
            data = io.BytesIO(cmsg[0][1][self.field])
            img = Image.open(data)
            if bmsg:
                boxes = np.fromstring(bmsg[0][1]['boxes'.encode('utf-8')][1:-1], sep=',')
                label += ' people: {}'.format(bmsg[0][1]['people'.encode('utf-8')].decode('utf-8'))
                for box in range(int(bmsg[0][1]['people'.encode('utf-8')])):  # Draw boxes
                    x1 = boxes[box*4]
                    y1 = boxes[box*4+1]
                    x2 = boxes[box*4+2]
                    y2 = boxes[box*4+3]
                    draw = ImageDraw.Draw(img)
                    draw.rectangle(((x1, y1), (x2, y2)), width=5, outline='red')
            arr = np.array(img)
            arr = cv2.cvtColor(arr, cv2.COLOR_BGR2RGB)
            cv2.putText(arr, label, (10, 40), cv2.FONT_HERSHEY_SIMPLEX, 0.7, (0,0,255), 1, cv2.LINE_AA)
            ret, img = cv2.imencode('.jpg', arr)
            return img.tobytes()
        else:
            # TODO: put an 'we're experiencing technical difficlties' image
            pass

def gen(stream):
    while True:
        frame = stream.get_last()
        if frame is None:
            break
        yield (b'--frame\r\n'
               b'Pragma-directive: no-cache\r\n'
               b'Cache-directive: no-cache\r\n'
               b'Cache-control: no-cache\r\n'
               b'Pragma: no-cache\r\n'
               b'Expires: 0\r\n'
               b'Content-Type: image/jpeg\r\n\r\n' + frame + b'\r\n\r\n')

conn = None
args = None
app = Flask(__name__)

@app.route('/video')
def video_feed():
    return Response(gen(RedisImageStream(conn, args)),
                    mimetype='multipart/x-mixed-replace; boundary=frame')

if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('camera', help='Input camera stream key', nargs='?', type=str, default='camera:0')
    parser.add_argument('boxes', help='Input model stream key', nargs='?', type=str, default='camera:0:yolo')
    parser.add_argument('--field', help='Image field name', type=str, default='image')
    parser.add_argument('--fmt', help='Frame storage format', type=str, default='.jpg')
    parser.add_argument('-u', '--url', help='Redis URL', type=str, default='redis://127.0.0.1:6379')
    args = parser.parse_args()

    # Set up Redis connection
    url = urlparse(args.url)
    conn = redis.Redis(host=url.hostname, port=url.port)
    if not conn.ping():
        raise Exception('Redis unavailable')

    app.run(host='0.0.0.0')