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@chapter Resampler Options

@c man begin RESAMPLER OPTIONS

The audio resampler supports the following named options.

Options may be set by specifying -@var{option} @var{value} in the

FFmpeg tools, @var{option}=@var{value} for the aresample filter,

by setting the value explicitly in the

@code{SwrContext} options or using the @file{libavutil/opt.h} API for

programmatic use.

@table @option

@item ich, in_channel_count

Set the number of input channels. Default value is 0. Setting this

value is not mandatory if the corresponding channel layout

@option{in_channel_layout} is set.

@item och, out_channel_count

Set the number of output channels. Default value is 0. Setting this

value is not mandatory if the corresponding channel layout

@option{out_channel_layout} is set.

@item uch, used_channel_count

Set the number of used input channels. Default value is 0. This option is

only used for special remapping.

@item isr, in_sample_rate

Set the input sample rate. Default value is 0.

@item osr, out_sample_rate

Set the output sample rate. Default value is 0.

@item isf, in_sample_fmt

Specify the input sample format. It is set by default to @code{none}.

@item osf, out_sample_fmt

Specify the output sample format. It is set by default to @code{none}.

@item tsf, internal_sample_fmt

Set the internal sample format. Default value is @code{none}.

This will automatically be chosen when it is not explicitly set.

@item icl, in_channel_layout

@item ocl, out_channel_layout

Set the input/output channel layout.

See @ref{channel layout syntax,,the Channel Layout section in the ffmpeg-utils(1) manual,ffmpeg-utils}

for the required syntax.

@item clev, center_mix_level

Set the center mix level. It is a value expressed in deciBel, and must be

in the interval [-32,32].

@item slev, surround_mix_level

Set the surround mix level. It is a value expressed in deciBel, and must

be in the interval [-32,32].

@item lfe_mix_level

Set LFE mix into non LFE level. It is used when there is a LFE input but no

LFE output. It is a value expressed in deciBel, and must

be in the interval [-32,32].

@item rmvol, rematrix_volume

Set rematrix volume. Default value is 1.0.

@item rematrix_maxval

Set maximum output value for rematrixing.

This can be used to prevent clipping vs. preventing volumn reduction

A value of 1.0 prevents cliping.

@item flags, swr_flags

Set flags used by the converter. Default value is 0.

It supports the following individual flags:

@table @option

@item res

force resampling, this flag forces resampling to be used even when the

input and output sample rates match.

@end table

@item dither_scale

Set the dither scale. Default value is 1.

@item dither_method

Set dither method. Default value is 0.

Supported values:

@table @samp

@item rectangular

select rectangular dither

@item triangular

select triangular dither

@item triangular_hp

select triangular dither with high pass

@item lipshitz

select lipshitz noise shaping dither

@item shibata

select shibata noise shaping dither

@item low_shibata

select low shibata noise shaping dither

@item high_shibata

select high shibata noise shaping dither

@item f_weighted

select f-weighted noise shaping dither

@item modified_e_weighted

select modified-e-weighted noise shaping dither

@item improved_e_weighted

select improved-e-weighted noise shaping dither

@end table

@item resampler

Set resampling engine. Default value is swr.

Supported values:

@table @samp

@item swr

select the native SW Resampler; filter options precision and cheby are not

applicable in this case.

@item soxr

select the SoX Resampler (where available); compensation, and filter options

filter_size, phase_shift, filter_type & kaiser_beta, are not applicable in this

case.

@end table

@item filter_size

For swr only, set resampling filter size, default value is 32.

@item phase_shift

For swr only, set resampling phase shift, default value is 10, and must be in

the interval [0,30].

@item linear_interp

Use Linear Interpolation if set to 1, default value is 0.

@item cutoff

Set cutoff frequency (swr: 6dB point; soxr: 0dB point) ratio; must be a float

value between 0 and 1.  Default value is 0.97 with swr, and 0.91 with soxr

(which, with a sample-rate of 44100, preserves the entire audio band to 20kHz).

@item precision

For soxr only, the precision in bits to which the resampled signal will be

calculated.  The default value of 20 (which, with suitable dithering, is

appropriate for a destination bit-depth of 16) gives SoX's 'High Quality'; a

value of 28 gives SoX's 'Very High Quality'.

@item cheby

For soxr only, selects passband rolloff none (Chebyshev) & higher-precision

approximation for 'irrational' ratios. Default value is 0.

@item async

For swr only, simple 1 parameter audio sync to timestamps using stretching,

squeezing, filling and trimming. Setting this to 1 will enable filling and

trimming, larger values represent the maximum amount in samples that the data

may be stretched or squeezed for each second.

Default value is 0, thus no compensation is applied to make the samples match

the audio timestamps.

@item first_pts

For swr only, assume the first pts should be this value. The time unit is 1 / sample rate.

This allows for padding/trimming at the start of stream. By default, no

assumption is made about the first frame's expected pts, so no padding or

trimming is done. For example, this could be set to 0 to pad the beginning with

silence if an audio stream starts after the video stream or to trim any samples

with a negative pts due to encoder delay.

@item min_comp

For swr only, set the minimum difference between timestamps and audio data (in

seconds) to trigger stretching/squeezing/filling or trimming of the

data to make it match the timestamps. The default is that

stretching/squeezing/filling and trimming is disabled

(@option{min_comp} = @code{FLT_MAX}).

@item min_hard_comp

For swr only, set the minimum difference between timestamps and audio data (in

seconds) to trigger adding/dropping samples to make it match the

timestamps.  This option effectively is a threshold to select between

hard (trim/fill) and soft (squeeze/stretch) compensation. Note that

all compensation is by default disabled through @option{min_comp}.

The default is 0.1.

@item comp_duration

For swr only, set duration (in seconds) over which data is stretched/squeezed

to make it match the timestamps. Must be a non-negative double float value,

default value is 1.0.

@item max_soft_comp

For swr only, set maximum factor by which data is stretched/squeezed to make it

match the timestamps. Must be a non-negative double float value, default value

is 0.

@item matrix_encoding

Select matrixed stereo encoding.

It accepts the following values:

@table @samp

@item none

select none

@item dolby

select Dolby

@item dplii

select Dolby Pro Logic II

@end table

Default value is @code{none}.

@item filter_type

For swr only, select resampling filter type. This only affects resampling

operations.

It accepts the following values:

@table @samp

@item cubic

select cubic

@item blackman_nuttall

select Blackman Nuttall Windowed Sinc

@item kaiser

select Kaiser Windowed Sinc

@end table

@item kaiser_beta

For swr only, set Kaiser Window Beta value. Must be an integer in the

interval [2,16], default value is 9.

@item output_sample_bits

For swr only, set number of used output sample bits for dithering. Must be an integer in the

interval [0,64], default value is 0, which means it's not used.

@end table

@c man end RESAMPLER OPTIONS