How to extract and synchronize images and odometry without playing back rosbag?

edit

I want to extract images and odometry from a rosbag. A possible way to do this would be to create a node subscribing to the topics using message_filters, then write a callback saving the data as it arrives.

I prefer not to playback the entire rosbag everytime I want to extract data. Instead, I'd like to load the data directly from the rosbag, then synchronize and save off the data.

However, I am not sure how to do this without writing my own code for synchronization. Is there a way to use the synchronization tools with the rosbags loaded in code instead of played back on the command line?