Xi Graphics has developed a record/playback method within the X server itself to perfrrm low-overhead recording of the incoming X protocol packets and other inputs to the X server while the X server is also performing its normal functions.

The recording operation capturres the data that causes the X server to generate the display being shown - data packets, mouse and keyboard inputs, etc. - along with time-of-day. Data are modified to allow a high level of compression either externally or within the X server itself. This reduces dramatically the volume of recording necessary. For large systems, this can be a sizeable benefit.

For more details, see SECAP and Recording UNIX/Linux X Sessions pdfs