As we know rosbag can be quite big. In many real world scenarios a considerable space is used by strings, since ros message use extensively names as identifiers (example: name of joint or frame_id).
LZ4 compression does a very good job in term of speed vs size reduction.
I wonder if raw rosbag might use hashed string to reduce the serialize size? It can be done quite easily, I think, using a library like this one https://github.com/foonathan/string_id
What do you think?
If the community consider this upgrade useful, I can try implementing it myself and do a pull request.