When the recorder is indexing data it is matching up its event data to stored recorded video.
Indexing can take up to several hours to complete, depending on the amount of of physical storage attached to the unit.
Once complete you will see motion and other event data available on the timeline bar.
The recorder does this to ensure that event data in the timeline search is accurate. Indexing will occur with every software update or reboot of the system.
The ability to export video may be hindered and searched video may not show event data on the timber.