Feature/sg 747 Adding utils to load/save videos (#815)

* first draft of load_video

* adding save_video, some parts are still to be checked

* wip

* cleaning

* fix rgb to bgr and remove check

src/super_gradients/training/utils/videos.py

@@ -0,0 +1,99 @@
+from typing import List, Optional, Tuple
+import cv2
+
+import numpy as np
+
+
+__all__ = ["load_video", "save_video"]
+
+
+def load_video(file_path: str, max_frames: Optional[int] = None) -> Tuple[List[np.ndarray], int]:
+    """Open a video file and extract each frame into numpy array.
+
+    :param file_path:   Path to the video file.
+    :param max_frames:  Optional, maximum number of frames to extract.
+    :return:
+                - Frames representing the video, each in (H, W, C), RGB.
+                - Frames per Second (FPS).
+    """
+    cap = _open_video(file_path)
+    frames = _extract_frames(cap, max_frames)
+    fps = cap.get(cv2.CAP_PROP_FPS)
+    cap.release()
+    return frames, fps
+
+
+def _open_video(file_path: str) -> cv2.VideoCapture:
+    """Open a video file.
+
+    :param file_path:   Path to the video file
+    :return:            Opened video capture object
+    """
+    cap = cv2.VideoCapture(file_path)
+    if not cap.isOpened():
+        raise ValueError(f"Failed to open video file: {file_path}")
+    return cap
+
+
+def _extract_frames(cap: cv2.VideoCapture, max_frames: Optional[int] = None) -> List[np.ndarray]:
+    """Extract frames from an opened video capture object.
+
+    :param cap:         Opened video capture object.
+    :param max_frames:  Optional maximum number of frames to extract.
+    :return:            Frames representing the video, each in (H, W, C), RGB.
+    """
+    frames = []
+
+    while max_frames != len(frames):
+        frame_read_success, frame = cap.read()
+        if not frame_read_success:
+            break
+        frames.append(cv2.cvtColor(frame, cv2.COLOR_BGR2RGB))
+
+    return frames
+
+
+def save_video(output_path: str, frames: List[np.ndarray], fps: int) -> None:
+    """Save a video locally.
+
+    :param output_path: Where the video will be saved
+    :param frames:      Frames representing the video, each in (H, W, C), RGB. Note that all the frames are expected to have the same shape.
+    :param fps:         Frames per second
+    """
+    video_height, video_width = _validate_frames(frames)
+
+    video_writer = cv2.VideoWriter(
+        output_path,
+        cv2.VideoWriter_fourcc(*"mp4v"),
+        fps,
+        (video_width, video_height),
+    )
+
+    for frame in frames:
+        video_writer.write(cv2.cvtColor(frame, cv2.COLOR_RGB2BGR))
+
+    video_writer.release()
+
+
+def _validate_frames(frames: List[np.ndarray]) -> Tuple[float, float]:
+    """Validate the frames to make sure that every frame has the same size and includes the channel dimension. (i.e. (H, W, C))
+
+    :param frames:  Frames representing the video, each in (H, W, C), RGB. Note that all the frames are expected to have the same shape.
+    :return:        (Height, Weight) of the video.
+    """
+    min_height = min(frame.shape[0] for frame in frames)
+    max_height = max(frame.shape[0] for frame in frames)
+
+    min_width = min(frame.shape[1] for frame in frames)
+    max_width = max(frame.shape[1] for frame in frames)
+
+    if (min_height, min_width) != (max_height, max_width):
+        raise RuntimeError(
+            f"Your video is made of frames that have (height, width) going from ({min_height}, {min_width}) to ({max_height}, {max_width}).\n"
+            f"Please make sure that all the frames have the same shape."
+        )
+
+    if set(frame.ndim for frame in frames) != {3} or set(frame.shape[-1] for frame in frames) != {3}:
+        raise RuntimeError("Your frames must include 3 channels.")
+
+    return max_height, max_width