Add LoadImages._cv2_rotate() (#9249)

Optional manual rotation code per iPhone rotation issue in https://github.com/ultralytics/yolov5/issues/8493

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

utils/dataloaders.py

@@ -213,7 +213,7 @@ class LoadImages:
         self.auto = auto
         self.transforms = transforms  # optional
         if any(videos):
-            self.new_video(videos[0])  # new video
+            self._new_video(videos[0])  # new video
         else:
             self.cap = None
         assert self.nf > 0, f'No images or videos found in {p}. ' \
@@ -238,10 +238,11 @@ class LoadImages:
                 if self.count == self.nf:  # last video
                     raise StopIteration
                 path = self.files[self.count]
-                self.new_video(path)
+                self._new_video(path)
                 ret_val, im0 = self.cap.read()
 
             self.frame += 1
+            # im0 = self._cv2_rotate(im0)  # for use if cv2 auto rotation is False
             s = f'video {self.count + 1}/{self.nf} ({self.frame}/{self.frames}) {path}: '
 
         else:
@@ -260,10 +261,23 @@ class LoadImages:
 
         return path, im, im0, self.cap, s
 
-    def new_video(self, path):
+    def _new_video(self, path):
+        # Create a new video capture object
         self.frame = 0
         self.cap = cv2.VideoCapture(path)
         self.frames = int(self.cap.get(cv2.CAP_PROP_FRAME_COUNT))
+        self.orientation = int(self.cap.get(cv2.CAP_PROP_ORIENTATION_META))  # rotation degrees
+        # self.cap.set(cv2.CAP_PROP_ORIENTATION_AUTO, 0)  # disable https://github.com/ultralytics/yolov5/issues/8493
+
+    def _cv2_rotate(self, im):
+        # Rotate a cv2 video manually
+        if self.orientation == 0:
+            return cv2.rotate(im, cv2.ROTATE_90_CLOCKWISE)
+        elif self.orientation == 180:
+            return cv2.rotate(im, cv2.ROTATE_90_COUNTERCLOCKWISE)
+        elif self.orientation == 90:
+            return cv2.rotate(im, cv2.ROTATE_180)
+        return im
 
     def __len__(self):
         return self.nf  # number of files