Discrepancy in topic displayed Hz

edit

Hi,

I've run in a strange situation. I've recorded in a rosbag a topic with should be publish at 100 Hz.

When playing back the bag with command-line instruction rosbag play, the topic is shown to be publish at 100.0 Hz (either by rostopic hz or by rqt topic_monitor). However, when I verify the callback rate of a subscriber subscribed to this topic, I get a much lower freq, around 20.0 Hz.

Now for the interesting part. When I open the same bag with rqt_bag and visually validate the message reception rate, I find the rate to be actually 20.0 Hz. Furthermore, if I play the bag from rqt_bag, the rate displayed is 20.0 Hz.

My question would be, why the displayed rate is incorrect with rosbag play?