Add new --vid-stride inference parameter for videos

classify/predict.py

@@ -66,6 +66,7 @@ def run(
         exist_ok=False,  # existing project/name ok, do not increment
         half=False,  # use FP16 half-precision inference
         dnn=False,  # use OpenCV DNN for ONNX inference
+        vid_stride=1,  # video frame-rate stride
 ):
     source = str(source)
     save_img = not nosave and not source.endswith('.txt')  # save inference images
@@ -88,10 +89,10 @@ def run(
     # Dataloader
     if webcam:
         view_img = check_imshow()
-        dataset = LoadStreams(source, img_size=imgsz, transforms=classify_transforms(imgsz[0]))
+        dataset = LoadStreams(source, img_size=imgsz, transforms=classify_transforms(imgsz[0]), vid_stride=vid_stride)
         bs = len(dataset)  # batch_size
     else:
-        dataset = LoadImages(source, img_size=imgsz, transforms=classify_transforms(imgsz[0]))
+        dataset = LoadImages(source, img_size=imgsz, transforms=classify_transforms(imgsz[0]), vid_stride=vid_stride)
         bs = 1  # batch_size
     vid_path, vid_writer = [None] * bs, [None] * bs
 
@@ -196,6 +197,7 @@ def parse_opt():
     parser.add_argument('--exist-ok', action='store_true', help='existing project/name ok, do not increment')
     parser.add_argument('--half', action='store_true', help='use FP16 half-precision inference')
     parser.add_argument('--dnn', action='store_true', help='use OpenCV DNN for ONNX inference')
+    parser.add_argument('--vid-stride', type=int, default=1, help='video frame-rate stride')
     opt = parser.parse_args()
     opt.imgsz *= 2 if len(opt.imgsz) == 1 else 1  # expand
     print_args(vars(opt))

detect.py

@@ -74,6 +74,7 @@ def run(
         hide_conf=False,  # hide confidences
         half=False,  # use FP16 half-precision inference
         dnn=False,  # use OpenCV DNN for ONNX inference
+        vid_stride=1,  # video frame-rate stride
 ):
     source = str(source)
     save_img = not nosave and not source.endswith('.txt')  # save inference images
@@ -96,10 +97,10 @@ def run(
     # Dataloader
     if webcam:
         view_img = check_imshow()
-        dataset = LoadStreams(source, img_size=imgsz, stride=stride, auto=pt)
+        dataset = LoadStreams(source, img_size=imgsz, stride=stride, auto=pt, vid_stride=vid_stride)
         bs = len(dataset)  # batch_size
     else:
-        dataset = LoadImages(source, img_size=imgsz, stride=stride, auto=pt)
+        dataset = LoadImages(source, img_size=imgsz, stride=stride, auto=pt, vid_stride=vid_stride)
         bs = 1  # batch_size
     vid_path, vid_writer = [None] * bs, [None] * bs
 
@@ -236,6 +237,7 @@ def parse_opt():
     parser.add_argument('--hide-conf', default=False, action='store_true', help='hide confidences')
     parser.add_argument('--half', action='store_true', help='use FP16 half-precision inference')
     parser.add_argument('--dnn', action='store_true', help='use OpenCV DNN for ONNX inference')
+    parser.add_argument('--vid-stride', type=int, default=1, help='video frame-rate stride')
     opt = parser.parse_args()
     opt.imgsz *= 2 if len(opt.imgsz) == 1 else 1  # expand
     print_args(vars(opt))

utils/dataloaders.py

@@ -187,7 +187,7 @@ def __iter__(self):
 
 class LoadImages:
     # YOLOv5 image/video dataloader, i.e. `python detect.py --source image.jpg/vid.mp4`
-    def __init__(self, path, img_size=640, stride=32, auto=True, transforms=None):
+    def __init__(self, path, img_size=640, stride=32, auto=True, transforms=None, vid_stride=1):
         files = []
         for p in sorted(path) if isinstance(path, (list, tuple)) else [path]:
             p = str(Path(p).resolve())
@@ -212,6 +212,7 @@ def __init__(self, path, img_size=640, stride=32, auto=True, transforms=None):
         self.mode = 'image'
         self.auto = auto
         self.transforms = transforms  # optional
+        self.vid_stride = vid_stride  # video frame-rate stride
         if any(videos):
             self._new_video(videos[0])  # new video
         else:
@@ -232,6 +233,7 @@ def __next__(self):
             # Read video
             self.mode = 'video'
             ret_val, im0 = self.cap.read()
+            self.cap.set(cv2.CAP_PROP_POS_FRAMES, self.vid_stride * (self.frame + 1))  # read at vid_stride
             while not ret_val:
                 self.count += 1
                 self.cap.release()
@@ -242,7 +244,7 @@ def __next__(self):
                 ret_val, im0 = self.cap.read()
 
             self.frame += 1
-            # im0 = self._cv2_rotate(im0)  # for use if cv2 auto rotation is False
+            # im0 = self._cv2_rotate(im0)  # for use if cv2 autorotation is False
             s = f'video {self.count + 1}/{self.nf} ({self.frame}/{self.frames}) {path}: '
 
         else:
@@ -265,7 +267,7 @@ 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.frames = int(self.cap.get(cv2.CAP_PROP_FRAME_COUNT) / self.vid_stride)
         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
 
@@ -285,11 +287,12 @@ def __len__(self):
 
 class LoadStreams:
     # YOLOv5 streamloader, i.e. `python detect.py --source 'rtsp://example.com/media.mp4'  # RTSP, RTMP, HTTP streams`
-    def __init__(self, sources='streams.txt', img_size=640, stride=32, auto=True, transforms=None):
+    def __init__(self, sources='streams.txt', img_size=640, stride=32, auto=True, transforms=None, vid_stride=1):
         torch.backends.cudnn.benchmark = True  # faster for fixed-size inference
         self.mode = 'stream'
         self.img_size = img_size
         self.stride = stride
+        self.vid_stride = vid_stride  # video frame-rate stride
         sources = Path(sources).read_text().rsplit() if Path(sources).is_file() else [sources]
         n = len(sources)
         self.sources = [clean_str(x) for x in sources]  # clean source names for later
@@ -329,11 +332,11 @@ def __init__(self, sources='streams.txt', img_size=640, stride=32, auto=True, tr
 
     def update(self, i, cap, stream):
         # Read stream `i` frames in daemon thread
-        n, f, read = 0, self.frames[i], 1  # frame number, frame array, inference every 'read' frame
+        n, f = 0, self.frames[i]  # frame number, frame array
         while cap.isOpened() and n < f:
             n += 1
             cap.grab()  # .read() = .grab() followed by .retrieve()
-            if n % read == 0:
+            if n % self.vid_stride == 0:
                 success, im = cap.retrieve()
                 if success:
                     self.imgs[i] = im