Compand

Audio Single output Transform

Compress or expand audio dynamic range.

FFmpeg filter: compand — the official reference.

Add it to a graph. The explicit form works for every filter — bind it to its input and read the result from outputs():

$node   = $audio->addFilter(new Compand(…));
$result = $node->outputs()[0];

Shorthand. Single-output filters can skip the node — apply() returns the result stream directly:

$result = $audio->apply(new Compand(…));

When to use it

TODO — when this filter shines: what it’s the right tool for, what to reach for instead when it isn’t, and how it composes with neighbouring filters.

How to use it

TODO — prose: how the filter actually works and what its key parameters mean (the explanation FFmpeg’s terse option help omits).

Examples

TODO — runnable PHP, with the equivalent ffmpeg CLI alongside.

Gotchas

TODO

See also

TODO

Parameters

Parameter	Type	Default	Range / values	Description
attacks	string	0	—	set time over which increase of volume is determined
decays	string	0.8	—	set time over which decrease of volume is determined
points	string	-70/-70|-60/-20|1/0	—	set points of transfer function
soft_knee	float	0.01	0.01–900	set soft-knee
gain	float	0	-900–900	set output gain
volume	float	0	-900–0	set initial volume
delay	float	0	0–20	set delay for samples before sending them to volume adjuster

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Maps to FFmpeg’s compand filter. Verified against ffmpeg n7.1.1.