Also called: Audio channel mapping, channel mapping, audio routing, audio configuration

Audio mapping is the process of defining how input audio tracks and channels feed the tracks and channels of an output media file. An audio map can copy or reorder channels, combine or split signals, attach external audio, and set properties such as channel layout, codec and language so that the output meets its delivery specification.

Detailed definition

What is audio mapping?

Audio mapping controls where audio goes when a media file is processed, transcoded, packaged or delivered. It connects selected audio from a source file or auxiliary file to specific tracks and channels in the output.

A track and a channel are not necessarily the same thing. An audio track is a stored sequence of audio data and may contain one channel, such as mono, or several channels, such as stereo or 5.1 surround sound. Audio mapping therefore operates at two related levels:

Track mapping: Selecting which input tracks become which output tracks.
Channel mapping: Assigning individual input channels, such as front left or centre, to positions in an output channel layout.

For example, a source master might contain a 5.1 programme mix, a stereo mix, an audio-description track and several dubbed-language tracks. Audio mapping determines which of these elements appear in each deliverable, in what order and with which technical labels.

How does audio mapping work?

An audio mapping configuration usually defines:

The source track, channel or external audio file to use.
The destination track and channel for each selected signal.
Whether a signal is copied, reordered, duplicated or mixed with other signals.
The required number and arrangement of output channels.
Output properties such as codec, bitrate, sample rate and language metadata.
Any gain values used when several input channels are combined.

Some mappings simply move audio without changing its content. Others use a mixing matrix to calculate each output channel from several inputs. A 5.1-to-stereo downmix, for example, normally combines the centre and surround channels with the left and right channels at defined gain levels.

Why is audio mapping important?

Broadcasters, streaming services and distribution partners may require different audio arrangements for the same programme. A technically valid file can still be rejected, played incorrectly or deliver the wrong language if its audio tracks are mapped in the wrong order.

Examples where Audio Mapping is needed

Produce stereo, surround and multi-language deliverables from the same master.
Match a broadcaster’s or platform’s required track allocation.
Keep dialogue, music and effects, audio description and dubbed versions correctly separated.
Maintain the relationship between audio content and metadata.
Automate repeatable transcoding and delivery workflows.
Converting 5.1 surround sound to stereo
Combining the left and right signals as a single mono track

Audio mapping compared with related processes

Audio mapping vs Audio mixing: Mapping determines the relationship between inputs and outputs. Mixing adjusts or combines signals to create a particular balance. A mapping can include mixing, but many maps only copy or reorder channels.
Audio mapping vs Downmixing: Downmixing is a specific type of audio mapping that combines a larger channel layout into fewer channels, such as 5.1 to stereo.
Audio mapping vs Channel layout: A channel layout describes the channels and their intended positions. Audio mapping determines how source channels are assigned to that layout.
Audio mapping vs Transcoding: Transcoding converts media into another encoding format or profile. Audio mapping is one part of a transcoding configuration.

In Knox Media Hub, Audio Mapping is a transcoding capability for creating custom output audio tracks. Configurations can join mono tracks, incorporate audio from auxiliary files, edit output-track properties and be saved as reusable presets.