If you look in your [install-dir]/logs directory you'll notice the _access.log and _error.log files. They should contain play and stop events along with any corresponding errors that occur.
As well, is the /conf/log4j.properties file, where you can modify or create new logging Appenders. A simple approach is to make sure you collect the data you need to look back case by case. A log row with x-event "destroy" for a c-client-id has cumulative totals: sc-bytes (server to client bytes, for playback clients), cs-bytes (client to server bytes, for publishing clients) and x-duration. It looks like you already have a way of
associating users with client-id.