afir

Apply an arbitrary Finite Impulse Response filter.

This filter is designed for applying long FIR filters, up to 60 seconds long.

It can be used as component for digital crossover filters, room equalization, cross talk cancellation, wavefield synthesis, auralization, ambiophonics, ambisonics and spatialization.

This filter uses the streams higher than first one as FIR coefficients. If the non-first stream holds a single channel, it will be used for all input channels in the first stream, otherwise the number of channels in the non-first stream must be same as the number of channels in the first stream.

It accepts the following parameters:

dry

Set dry gain. This sets input gain.

wet

Set wet gain. This sets final output gain.

length

Set Impulse Response filter length. Default is 1, which means whole IR is processed.

gtype

This option is deprecated, and does nothing.

irnorm

Set norm to be applied to IR coefficients before filtering. Allowed range is from -1 to 2. IR coefficients are normalized with calculated vector norm set by this option. For negative values, no norm is calculated, and IR coefficients are not modified at all. Default is 1.

irlink

For multichannel IR if this option is set to true, all IR channels will be normalized with maximal measured gain of all IR channels coefficients as set by irnorm option. When disabled, all IR coefficients in each IR channel will be normalized independently. Default is true.

irgain

Set gain to be applied to IR coefficients before filtering. Allowed range is 0 to 1. This gain is applied after any gain applied with irnorm option.

irfmt

Set format of IR stream. Can be mono or input. Default is input.

maxir

Set max allowed Impulse Response filter duration in seconds. Default is 30 seconds. Allowed range is 0.1 to 60 seconds.

response

This option is deprecated, and does nothing.

channel

This option is deprecated, and does nothing.

size

This option is deprecated, and does nothing.

rate

This option is deprecated, and does nothing.

minp

Set minimal partition size used for convolution. Default is 8192. Allowed range is from 1 to 65536. Lower values decreases latency at cost of higher CPU usage.

maxp

Set maximal partition size used for convolution. Default is 8192. Allowed range is from 8 to 65536. Lower values may increase CPU usage.

nbirs

Set number of input impulse responses streams which will be switchable at runtime. Allowed range is from 1 to 32. Default is 1.

ir

Set IR stream which will be used for convolution, starting from 0, should always be lower than supplied value by nbirs option. Default is 0. This option can be changed at runtime via commands.

precision

Set which precision to use when processing samples.

auto

Auto pick internal sample format depending on other filters.

float

Always use single-floating point precision sample format.

double

Always use double-floating point precision sample format.

Default value is auto.

irload

Set when to load IR stream. Can be init or access. First one load and prepares all IRs on initialization, second one once on first access of specific IR. Default is init.

Examples

• Apply reverb to stream using mono IR file as second input, complete command using ffmpeg:

  ffmpeg -i input.wav -i middle_tunnel_1way_mono.wav -lavfi afir output.wav
  

• Apply true stereo processing given input stereo stream, and two stereo impulse responses for left and right channel, the impulse response files are files with names l_ir.wav and r_ir.wav, and setting irnorm option value:

  "pan=4C|c0=FL|c1=FL|c2=FR|c3=FR[a];amovie=l_ir.wav[LIR];amovie=r_ir.wav[RIR];[LIR][RIR]amerge[ir];[a][ir]afir=irfmt=input:irnorm=1.2,pan=stereo|FL<c0+c2|FR<c1+c3"
  

• Similar to above example, but with irgain explicitly set to estimated value and with irnorm disabled:

  "pan=4C|c0=FL|c1=FL|c2=FR|c3=FR[a];amovie=l_ir.wav[LIR];amovie=r_ir.wav[RIR];[LIR][RIR]amerge[ir];[a][ir]afir=irfmt=input:irgain=-5dB:irnom=-1,pan=stereo|FL<c0+c2|FR<c1+c3"