\input texinfo @c -*- texinfo -*-

@settitle FFmpeg Resampler Documentation
@titlepage
@center @titlefont{FFmpeg Resampler Documentation}
@end titlepage

@top

@contents

@chapter Description
@c man begin DESCRIPTION

The FFmpeg resampler provides an high-level interface to the
libswresample library audio resampling utilities. In particular it
allows to perform audio resampling, audio channel layout rematrixing,
and convert audio format and packing layout.

@c man end DESCRIPTION

@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 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}.

@item icl, in_channel_layout
Set the input channel layout.

@item ocl, out_channel_layout
Set the output channel layout.

@item clev, center_mix_level
Set center mix level. It is a value expressed in deciBel, and must be
inclusively included between -32 and +32.

@item slev, surround_mix_level
Set surround mix level. It is a value expressed in deciBel, and must
be inclusively included between -32 and +32.

@item lfe_mix_evel
Set LFE mix level.

@item rmvol, rematrix_volume
Set rematrix volume. Default value is 1.0.

@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
@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
@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, must be included
between 0 and 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 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 included between
2 and 16, default value is 9.

@end table

@c man end RESAMPLER OPTIONS

@chapter See Also

@ifhtml
@url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
@url{libswresample.html,libswresample}
@end ifhtml

@ifnothtml
ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), libswresample(3)
@end ifnothtml

@include authors.texi

@ignore

@setfilename ffmpeg-resampler
@settitle FFmpeg Resampler

@end ignore

@bye
