adding blocking and non-blocking rtsp stream

This might fix the stream errors in issue #25
Also refactored the code a bit since we do not want to display a window from within the API (offload to the person implementing it).

examples/streaming_video.py

@@ -0,0 +1,82 @@
+import cv2
+
+from Camera import Camera
+
+
+def non_blocking():
+    print("calling non-blocking")
+
+    def inner_callback(img):
+        cv2.imshow("name", maintain_aspect_ratio_resize(img, width=600))
+        print("got the image non-blocking")
+        key = cv2.waitKey(1)
+        if key == ord('q'):
+            cv2.destroyAllWindows()
+            exit(1)
+
+    c = Camera("192.168.1.112", "admin", "jUa2kUzi")
+    # t in this case is a thread
+    t = c.open_video_stream(callback=inner_callback)
+
+    print(t.isAlive())
+    while True:
+        if not t.isAlive():
+            print("continuing")
+            break
+        # stop the stream
+        # client.stop_stream()
+
+
+def blocking():
+    c = Camera("192.168.1.112", "admin", "jUa2kUzi")
+    # stream in this case is a generator returning an image (in mat format)
+    stream = c.open_video_stream()
+
+    # using next()
+    # while True:
+    #     img = next(stream)
+    #     cv2.imshow("name", maintain_aspect_ratio_resize(img, width=600))
+    #     print("got the image blocking")
+    #     key = cv2.waitKey(1)
+    #     if key == ord('q'):
+    #         cv2.destroyAllWindows()
+    #         exit(1)
+
+    # or using a for loop
+    for img in stream:
+        cv2.imshow("name", maintain_aspect_ratio_resize(img, width=600))
+        print("got the image blocking")
+        key = cv2.waitKey(1)
+        if key == ord('q'):
+            cv2.destroyAllWindows()
+            exit(1)
+
+
+# Resizes a image and maintains aspect ratio
+def maintain_aspect_ratio_resize(image, width=None, height=None, inter=cv2.INTER_AREA):
+    # Grab the image size and initialize dimensions
+    dim = None
+    (h, w) = image.shape[:2]
+
+    # Return original image if no need to resize
+    if width is None and height is None:
+        return image
+
+    # We are resizing height if width is none
+    if width is None:
+        # Calculate the ratio of the height and construct the dimensions
+        r = height / float(h)
+        dim = (int(w * r), height)
+    # We are resizing width if height is none
+    else:
+        # Calculate the ratio of the 0idth and construct the dimensions
+        r = width / float(w)
+        dim = (width, int(h * r))
+
+    # Return the resized image
+    return cv2.resize(image, dim, interpolation=inter)
+
+
+# Call the methods. Either Blocking (using generator) or Non-Blocking using threads
+# non_blocking()
+blocking()