Thirteen lessons that walk every audio codec a video product might ship — from the legacy MP2/MP3 baseline to the modern frontier of Opus, xHE-AAC, AC-4, LC3, and USAC. We cover the technical guts (sub-band coding, MDCT, parametric stereo, SBR), the trade-offs that matter in production (bitrate vs latency vs CPU vs licensing), the patent and royalty landscape, and decision frameworks for OTT, broadcast, conferencing, and resource-constrained Bluetooth audio.