The long term reference picture is an important encoding feature that improves compression efficiency and video quality. In case of videos with a static background, it allows encoding the background scene with high quality for better motion compensation. This feature can be used in video conferences and surveillance applications. This feature can also be used in packet loss scenarios where P-frame can be used instead of traditional intra-frame (I-frame) to reconstruct the frame.
For more information, see Long Term Reference Picture in H.264/H.265 Video Codec Unit LogiCORE IP Product Guide (PG252).