Surround

Audio Single output Transform

Apply audio surround upmix filter.

FFmpeg filter: surround — 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 Surround(…));
$result = $node->outputs()[0];

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

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

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
chl_out	string	—	—	set output channel layout
chl_in	string	—	—	set input channel layout
level_in	float	1	0–10	set input level
level_out	float	1	0–10	set output level
lfe	bool	true	—	output LFE
lfe_low	int	128	0–256	LFE low cut off
lfe_high	int	256	0–512	LFE high cut off
lfe_mode	SurroundLfeMode	add	add, sub	set LFE channel mode
smooth	float	0	0–1	set temporal smoothness strength
angle	float	90	0–360	set soundfield transform angle
focus	float	0	-1–1	set soundfield transform focus
fc_in	float	1	0–10	set front center channel input level
fc_out	float	1	0–10	set front center channel output level
fl_in	float	1	0–10	set front left channel input level
fl_out	float	1	0–10	set front left channel output level
fr_in	float	1	0–10	set front right channel input level
fr_out	float	1	0–10	set front right channel output level
sl_in	float	1	0–10	set side left channel input level
sl_out	float	1	0–10	set side left channel output level
sr_in	float	1	0–10	set side right channel input level
sr_out	float	1	0–10	set side right channel output level
bl_in	float	1	0–10	set back left channel input level
bl_out	float	1	0–10	set back left channel output level
br_in	float	1	0–10	set back right channel input level
br_out	float	1	0–10	set back right channel output level
bc_in	float	1	0–10	set back center channel input level
bc_out	float	1	0–10	set back center channel output level
lfe_in	float	1	0–10	set lfe channel input level
lfe_out	float	1	0–10	set lfe channel output level
allx	float	-1	-1–15	set all channel’s x spread
ally	float	-1	-1–15	set all channel’s y spread
fcx	float	0.5	0.06–15	set front center channel x spread
flx	float	0.5	0.06–15	set front left channel x spread
frx	float	0.5	0.06–15	set front right channel x spread
blx	float	0.5	0.06–15	set back left channel x spread
brx	float	0.5	0.06–15	set back right channel x spread
slx	float	0.5	0.06–15	set side left channel x spread
srx	float	0.5	0.06–15	set side right channel x spread
bcx	float	0.5	0.06–15	set back center channel x spread
fcy	float	0.5	0.06–15	set front center channel y spread
fly	float	0.5	0.06–15	set front left channel y spread
fry	float	0.5	0.06–15	set front right channel y spread
bly	float	0.5	0.06–15	set back left channel y spread
bry	float	0.5	0.06–15	set back right channel y spread
sly	float	0.5	0.06–15	set side left channel y spread
sry	float	0.5	0.06–15	set side right channel y spread
bcy	float	0.5	0.06–15	set back center channel y spread
win_size	int	4096	1024–65536	set window size
win_func	SurroundWinFunc	hanning	rect, bartlett, hanning, hamming, blackman, welch, flattop, bharris, …	set window function
overlap	float	0.5	0–1	set window overlap

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