Smart codec is a vendor implementation of video compression that adjusts encoding effort to what the scene contains. It may raise the frame rate when motion appears, drop it when the scene is still, or spend more bits on a selected region while leaving the background coarser.
The name is a marketing label rather than a standard. Two cameras advertising smart codec can behave very differently, so the only meaningful comparison is the footage and storage they actually produce.
What it changes
Bit rate, frame rate and quantization are varied automatically, often with a region of interest receiving more detail. The storage savings are real when a scene is quiet for most of the day.
What to check
Confirm that motion still records at a usable frame rate and that a selected region stays sharp at night. Check compatibility with the recorder and with any analytics running downstream.