rosbag play - skip every Nth file

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I don't know of any way you can do this with the standard command line tools. However if you don't mind getting your hands dirty, you could use the rosbag_api to write a simple node that published the sensor messages from a bag at the desired rate.

The example on the page I linked to prints every message out on the screen. But you would want to modify it so that it only publishes messages on the desired topic, and at the rate you want.

Hope this helps.