Event stream
The event stream is the ordered sequence of timestamped events that makes up a session recording, from the opening full snapshot through every incremental change. It is the recording's storage format, transport format, and analysis substrate at once: replay is just one consumer of the stream.
How it works
Each event is a JSON object with a type, a data payload, and a millisecond timestamp. Order matters absolutely, because incremental events form a dependency chain on prior state. Streams are typically batched in the emit callback and shipped to a backend every few seconds, or pushed continuously over a socket for live use (see WebSocket ingest). Because the stream is structured data rather than pixels, it can be queried, diffed, summarized, and fed to models.
Where you encounter it
As the JSON files or database rows a replay backend stores, as the events array handed to Replayer, and as the input to any AI analyzing sessions. The format details live on the rrweb event page.