Go to documentation repository
...
If video resolution was changed during export, then the exported file will be divided into several parts containing archive intervals with different resolutions. If the UseFfmpegConcat registry key is enabled to merge such parts into one file (for details, see Registry keys reference guide), the exported file will be in MKV format regardless of the selected container type. If only codec (not the resolution) was changed during export, then the exported file won’t be divided into parts. The change of codec and resolution can be caused by selection of different streams for recording upon alarm and continuous recording—see Configuration of multistream video.
...