JOC (Joint Object Coding) is the technology that lets Dolby Atmos travel inside an E-AC-3 stream, and it is how immersive audio actually reaches most homes today. Rather than send dozens of discrete object streams, JOC carries a standard 5.1 core plus a compact set of metadata that describes how to reconstruct the Atmos objects from that core at the decoder. This keeps the bitrate manageable for streaming while preserving the height and object positioning of the immersive mix, and it stays backward compatible — a non-Atmos device just plays the 5.1 core. Netflix, Disney+, and others deliver Atmos as E-AC-3 JOC, with AC-4 IMS as the more efficient next-generation alternative.
