An adaptive loop filter is a component of a video codec that is used to reduce noise and improve the visual quality of compressed video. The adaptive loop filter operates by adjusting the filter coefficients in real-time based on the properties of the input video data. The goal of the adaptive loop filter is to remove artifacts and blockiness that can occur during video compression, while preserving as much detail as possible. The filter coefficients are typically adjusted using a feedback loop that analyzes the output of the filter and adjusts the coefficients to minimize the difference between the input and output signals. Adaptive loop filters can be implemented in various types of video codecs, including H.264, HEVC, and AV1. They are an essential component of modern video compression algorithms, as they enable high-quality video to be compressed efficiently while minimizing visual artifacts.