This block explains why raw digital video is extremely large and why compression is essential for storing, processing, and distributing video efficiently. Readers learn the main ideas behind video compression: bitrate, lossy and lossless compression, spatial redundancy inside a frame, temporal redundancy between frames, entropy coding, and psycho-visual optimization. The block shows how codecs take advantage of patterns in video: similar pixels, repeated motion, predictable changes between frames, and details the human eye is less likely to notice. It gives readers a practical mental model for understanding how compression works and what trade-offs it creates between file size, quality, encoding speed, and complexity.