images published out of order

[MFernandezCarmona]

Hi,
I'm using usb_cam_node_exe node in Humble and image_raw messages are being published out of (temporal) order.

Steps to reproduce:

1. Plug usb camera (tried two different ones)

2. Run usb_cam_node_exe node

ros2 run usb_cam usb_cam_node_exe --ros-args -r __ns:=/camera

3.Create a simple python node to check image timestamps:

import rclpy
from rclpy.node import Node
from sensor_msgs.msg import Image
from rclpy.time import Time

class ImageTimestampSubscriber(Node):
    def __init__(self):
        super().__init__('image_timestamp_subscriber')
        self.subscription = self.create_subscription(
            Image,
            '/camera/image_raw',
            self.image_callback,
            10
        )       

    def image_callback(self, msg):
        if hasattr(self,'last_time'):
            time_diff = Time.from_msg(msg.header.stamp) - self.last_time
            if time_diff.nanoseconds<0.0:
                self.get_logger().info(f" image ts dif: {time_diff.nanoseconds/1e6} ms")

        self.last_time = Time.from_msg(msg.header.stamp)

def main(args=None):
    rclpy.init(args=args)
    node = ImageTimestampSubscriber()
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()

4.Python script output shows that some messages are not in order:

[INFO] [1688644345.950392161] [image_timestamp_subscriber]:  image ts dif: -964.004 ms
[INFO] [1688644346.950561701] [image_timestamp_subscriber]:  image ts dif: -967.999 ms
[INFO] [1688644347.958506978] [image_timestamp_subscriber]:  image ts dif: -967.996 ms
[INFO] [1688644348.930496476] [image_timestamp_subscriber]:  image ts dif: -964.003 ms
[INFO] [1688644349.938465496] [image_timestamp_subscriber]:  image ts dif: -967.999 ms
[INFO] [1688644350.942504378] [image_timestamp_subscriber]:  image ts dif: -968.0 ms
[INFO] [1688644351.950476913] [image_timestamp_subscriber]:  image ts dif: -967.996 ms
[INFO] [1688644352.958440612] [image_timestamp_subscriber]:  image ts dif: -964.004 ms

Any ideas on what might be wrong?
Thanks

[MFernandezCarmona]

Wrong package! My apologies

[klintan]

I was about to say, I have never seen this. But to be honest I haven't tested out the timestamp on the published images in this package either. If you see any other problems with the package let me know :)

[MFernandezCarmona]

Actually, I'll try to reproduce the bug with your package, it could tell us where the problem is.
Cheers