# audioChannelFormat

## Description

An audioChannelFormat represents a single sequence of audio samples on which some action may be performed, such as movement of an object, which is rendered in a scene. It contains one or more audioBlockFormats, which sub-divide it in the time domain. The typeDefinition/typeLabel is used to define the type of channel.

The types of audioChannelFormats are:

## Common Attributes

Attribute Description Example Required
audioChannelFormatName Name of the channel FrontLeft Yes
audioChannelFormatID ID of the channel. The yyyy digits of AC_yyyyxxxx_represent the type of audio contained in the channel. The xxxx digits should match the audioStreamFormat xxxx digits. AC_00010001 Yes
typeLabel Descriptor of the type of channel 0001 Optional
typeDefinition Description of the type of channel DirectSpeakers Optional

* At least one of typeLabel or typeDefinition is required.

The typeDefinition of the audioChannelFormat specifies the type of audio it is describing, and also determines which parameters are used within its audioBlockFormat children.

## Common Sub-elements

Sub-element Description Attributes Quantity
audioBlockFormat Time division of channel containing dynamic metadata 1...*
frequency Sets a high or low cut-off frequency for the audio in Hz typeDefinition = “lowPass" or “highPass" 0...2

## audioBlockFormat

An audioBlockFormat represents a single sequence of audioChannelFormat samples with fixed parameters, including position, within a specified time interval.

### Attributes

Attribute Description Example Required Default
audioBlockFormatID ID for block AB_00010001_00000001 Yes
rtime Start time of block (relative to the start time of the parent audioObject) 00:00:00.00000 Optional 00:00:00.00000
duration Duration time of block. 00:00:10.00000 Optional unbounded duration

The last 8 hexadecimal digits in the audioBlockFormatID contain the index for the block within the channel, starting at 00000001 for the first block. If rtime is not used then the block starts at 00:00:00.00000. If duration is not used then the block lasts for the whole duration of the channel. If there is only one audioBlockFormat within an audioChannelFormat it is assumed to be a ‘static’ object that lasts the duration of the channel, therefore rtime and duration should be omitted. When there is more than one audioBlockFormat within an audioChannelFormat it is assumed to be a ‘dynamic’ object, therefore both rtime and duration should be used.

#### Time Format

The time is shown in the format ‘hh:mm:ss.zzzzz’ which indicate hours, minutes, seconds and fractional seconds.

### Sub-elements

The sub-elements within audioBlockFormat depend upon the typeDefinition/typeLabel of the audioChannelFormat.