Revision history [back]

rosbag timestamps and records messages in the order that they're received. If the messages on topic1 are much larger and take longer to serialize and transmit, they may arrive later even if they're queued for transmission first.

Adding a header won't help rosbag order messages properly; it will still use the receive timestamp. That said, having a header with a timestamp is useful for lots of other things. You can also reorder the messages in a bag file based on their header timestamps: http://wiki.ros.org/rosbag/Cookbook