adds example NV12 encoded video #30

rerun/examples/nv12/README.md

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+# nv12 
+> displays an NV12 encoded video stream from a webcam in rerun.
+
+
+## Download scripts
+```
+wget  https://raw.githubusercontent.com/rerun-io/rerun/main/examples/python/nv12/requirements.txt
+wget  https://raw.githubusercontent.com/rerun-io/rerun/main/examples/python/nv12/main.py
+```
+
+
+## Run scripts
+mamba activate rrVE
+pip install -r requirements.txt
+python main.py
+
+
+## Reference
+https://github.com/rerun-io/rerun/tree/main/examples/python/nv12 
+https://learn.microsoft.com/en-us/windows/win32/medfound/recommended-8-bit-yuv-formats-for-video-rendering 
+
+

rerun/examples/nv12/main.py

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+#!/usr/bin/env python3
+"""
+Stream NV12 images from a webcam.
+
+Run:
+```sh
+pip install -r examples/python/nv12/requirements.txt
+python examples/python/nv12/main.py
+```
+"""
+from __future__ import annotations
+
+import argparse
+import time
+
+import cv2
+import numpy as np
+import numpy.typing as npt
+import rerun as rr  # pip install rerun-sdk
+
+
+def bgr2nv12(bgr: npt.NDArray[np.uint8]) -> npt.NDArray[np.uint8]:
+    yuv: npt.NDArray[np.uint8] = cv2.cvtColor(bgr, cv2.COLOR_BGR2YUV_I420)
+    uv_row_cnt = yuv.shape[0] // 3
+    uv_plane = np.transpose(yuv[uv_row_cnt * 2 :].reshape(2, -1), [1, 0])
+    yuv[uv_row_cnt * 2 :] = uv_plane.reshape(uv_row_cnt, -1)
+    return yuv
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description="Example of using the Rerun visualizer to display NV12 images.")
+    rr.script_add_args(parser)
+    parser.add_argument(
+        "-t",
+        "--timeout",
+        type=float,
+        default=5,
+        help="Timeout in seconds, after which the script will stop streaming frames.",
+    )
+    args = parser.parse_args()
+
+    rr.script_setup(args, "rerun_example_nv12")
+
+    cap = cv2.VideoCapture(0)
+    if not cap.isOpened():
+        raise RuntimeError("This example requires a webcam.")
+    start_time = time.time()
+    print(f"Started streaming NV12 images for {args.timeout} seconds.")
+    while start_time + args.timeout > time.time():
+        ret, frame = cap.read()
+        if not ret:
+            time.sleep(0.01)
+            continue
+        rr.log(
+            "NV12",
+            rr.ImageEncoded(
+                contents=bytes(bgr2nv12(frame)),
+                format=rr.ImageFormat.NV12((frame.shape[0], frame.shape[1])),
+            ),
+        )
+        time.sleep(0.01)
+    rr.script_teardown(args)
+
+
+if __name__ == "__main__":
+    main()

rerun/examples/nv12/requirements.txt

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+rerun-sdk>=0.10
+opencv-python
+numpy