How to filter tfs in a bag file

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Hi,

I got a bag file that includes a huge number of a certain tf message. I want to filter out this special message, but all other tf should not be considered? How can I filter out just all tf messages with a certain frame_id and child_frame_id?

Something like

rosbag filter source.bag filtered.bag 'topic!="\tf" or m.transforms[0].header.child_frame_id != "odom"'

does not work and generates an error message (as expected)

AttributeError: '_std_msgs__Header' object has no attribute 'child_frame_id'

Thanks for your help

Poseidonius