In order to make profile editing easier and shorter, custom variables can be assigned and used inside the profile values. You may want to check the variables section to adjust them according to your FFmpeg version.

Variable declarations have the following format:
{$var.identifier} = value

$var
All variable declarations include this keyword.

identifier
Name that identifies the variable value. The value for "identifier" must be unique and can contain the following characters: "-", "_", a-z, A-Z, 0-9

value
The value to assign to the variable. Values cannot contain other variables and are limited to a single line.

Check the default profiles for examples of their usage.