Working with Dolby Metadata

Audio encoded with a Dolby codec always includes Dolby metadata, as per the ATSC A/52 2012 standard. This Dolby metadata is used by AWS Elemental Server in two ways when the stream is encoded with Dolby codec:

• It is used to manipulate the audio just before encoding the output.

• It is included in the metadata for the output stream.

This document describes how to set up an AWS Elemental Server profile or job to use Dolby metadata in these ways.

Dolby metadata is supported in the output only when the audio codec for the output is Dolby Digital (also known as AC3) or Dolby Digital Plus (also known as Enhanced AC3).

Topics

• Categories of Metadata: Delivered and Encoder Control
• Source of AWS Elemental Server Metadata
• Impact of the Metadata on the Output Audio
• Combinations of Input and Output Codec
• Setting Up the Profile or Event Using the Web Interface
• Output with the Dolby Digital Codec
• Output with Dolby Digital Plus (EC2, EAC3) Codec

Categories of Metadata: Delivered and Encoder Control

There are two categories of parameters in the Dolby metadata, characterized by how AWS Elemental Server uses it:

• Delivered: AWS Elemental Server does not read these parameters, so they have no effect on the audio produced by AWS Elemental Server. Instead, they are included as metadata in the output in order to deliver them to the downstream decoder.

  “Delivered” metadata is also called Consumer metadata because it is intended to be used by the end consumer’s home decoder.

• Encoder Control: AWS Elemental Server uses these parameters to manipulate the audio just before encoding the stream and producing the output. They provide a mechanism for AWS Elemental Server to control the transcoding performed by AWS Elemental Server. These parameters are never included in the output metadata.

  “Encoder Control” metadata is also called Professional metadata because it is intended to be used by a professional device – in our case AWS Elemental Server. It is never intended for the end consumer's home decoder.

Source of AWS Elemental Server Metadata

The metadata that AWS Elemental Server emits can come from one of two sources:

• Metadata that is already in the source. Only audio sources that use a Dolby codec can include this metadata. Different Dolby codecs include different categories of metadata as shown in this table.

  Codec	Categories Present
  Dolby Digital or Dolby Digital Plus	Delivered only
  Dolby E	Delivered and Encoder Control

• Metadata that is specified by completing metadata fields in the profile or event. You can specify this metadata in any audio whose output codec is a Dolby codec. In other words, you can add it when the audio source is not a Dolby codec as long as the output audio uses a Dolby codec.

  Both categories of metadata can be specified when specifying this source.

You specify the source when setting up the profile or event.

Impact of the Metadata on the Output Audio

Regardless of the source of the metadata, it affects the audio (either by manipulating encoder control or by being included in the output metadata) but only if the output codec is Dolby Digital or Dolby Digital Plus.

Combinations of Input and Output Codec

The possible input and output codec combinations (in which at least one codec is a Dolby codec) are as follows. All these combinations support including metadata in the output.

Input Codec	Output Codec
Dolby Digital or Dolby Digital Plus	Dolby Digital or Dolby Digital Plus
Dolby Digital	Dolby Digital Passthrough (so Dolby Digital audio is passed through; it is not transcoded)
Dolby Digital Plus	Dolby Digital Passthrough (so Dolby Digital Plus audio is passed through; it is not transcoded)
Mix of Dolby Digital Plus and another codec	Dolby Digital Plus (with the Automatic Passthrough field checked)
Dolby E	Dolby Digital
Dolby E	Dolby Digital Plus
Dolby E	Dolby E (passthrough )
A non-Dolby codec	Dolby Digital or Dolby Digital Plus

The sample rate when encoding with a Dolby codec is always 48000.