This is your Swiss Army knife.
In dark scenes or fast-moving action, you may notice "blocking" or "banding" (where colors don't blend smoothly). highly compressed movies and tv shows
Compression works by removing redundant data. Video files in their raw form can reach hundreds of gigabytes or even terabytes . To make these playable over standard internet connections, codecs (like H.264, H.265/HEVC, or AV1) shrink them into smaller packages: This is your Swiss Army knife