how to just use it in rosbag

[Jackie2chen]

How to use this to serialize storage and reading in the form of proto in rosbag? Do I still need to rely on rmw_ecal?

[FlorianReimold]

Rosbag is a custom format and does not support protobuf. If I recall correctly, it is some kind of SQL (light?) database. Anyways, if you want to store data in protobuf format, you can take a look at eCAL, yes. It will store the binary data (=> protobuf, if the message is protobuf encoded) in HDF5 files.