Overview

Dolby professional audio formats provide much more than just audio compression. The carriage of audio metadata preserves artistic intent along the delivery chain, enables loudness managment and supports new use cases.

Legacy Dolby Professional Audio Metadata

When the Dolby Digital and Dolby E codecs were released, a metadata system to support the carriage of multichannel audio was introduced. This metadata was carried over Dolby E and then either applied or inserted by the Dolby Digital Professional Encoder. The metadata fields were documented in SMPTE RDD6. The mechanism for embedding this metadata into the vertical ancillary space of an SDI stream was standardized in SMPTE ST 2020.

Dolby Metadata Guide

Dolby Professional Audio Metadata for Next Generation Audio (PMD)

As content providers look beyond multichannel audio to next generation audio, certain categories of features have been identified:

  • Immersive - addition of height channels
  • Accessible - support for audio description, dialogue enhancement and multi-language
  • Personalized - user customization such as commentary or sports team selection
  • Consistent - great experience across all device types

Enabling these feature sets has required reworking of Dolby's professional audio metadata formats resulting in what is called Professional Metadata Data (PMD). The bitstream payload for PMD is defined in SMPTE RDD 49 or in PMD Payload Specification. The carriage mechanims for transport of PMD over AES3 are standardized in SMPTE ST 2109. For legacy circuits, such as backhaul from an event, PMD can be carried by Dolby ED2. More information can be found at Professional Metadata (PMD).