import av
import cv2
import time

DEVICE = "/dev/video4"
TARGET_FPS = 30
WIDTH = 1280
HEIGHT = 720

# Open v4l2 device with same style options as ffmpeg CLI
container = av.open(
    DEVICE,
    format="v4l2",
    options={
        "input_format": "mjpeg",
        "video_size": f"{WIDTH}x{HEIGHT}",
        "framerate": str(TARGET_FPS),
    },
)

stream = container.streams.video[0]
frame_count = 0
t_start = time.perf_counter()

for frame in container.decode(stream):
    t0 = time.perf_counter()
    img = frame.to_ndarray(format="bgr24")  # OpenCV-compatible
    t1 = time.perf_counter()

    cv2.imshow("pyav_cam", img)
    key = cv2.waitKey(1) & 0xFF
    t2 = time.perf_counter()

    frame_count += 1
    if frame_count % 30 == 0:
        elapsed = t2 - t_start
        print(
            f"Frame {frame_count}: convert={1000*(t1-t0):.1f}ms, "
            f"imshow+waitKey={1000*(t2-t1):.1f}ms, avg_fps={frame_count/elapsed:.1f}"
        )

    if key == ord("q"):
        break

container.close()
cv2.destroyAllWindows()