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After making some blind tests on a small collection of music samples for home usage. It turned out that the default cutoff was too low. The impact of filter_size was not clearly distinguishable (the results were on the edge) with the music samples but turned out to be clearly audible in some synthetic samples. Thanks to Daniel for helping out with the listening tests. Signed-off-by: Alexander Strasser <eclipse7@gmx.net>
231 lines
6.2 KiB
Plaintext
231 lines
6.2 KiB
Plaintext
\input texinfo @c -*- texinfo -*-
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@settitle FFmpeg Resampler Documentation
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@titlepage
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@center @titlefont{FFmpeg Resampler Documentation}
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@end titlepage
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@top
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@contents
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@chapter Description
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@c man begin DESCRIPTION
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The FFmpeg resampler provides an high-level interface to the
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libswresample library audio resampling utilities. In particular it
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allows to perform audio resampling, audio channel layout rematrixing,
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and convert audio format and packing layout.
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@c man end DESCRIPTION
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@chapter Resampler Options
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@c man begin RESAMPLER OPTIONS
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The audio resampler supports the following named options.
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Options may be set by specifying -@var{option} @var{value} in the
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FFmpeg tools, @var{option}=@var{value} for the aresample filter,
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by setting the value explicitly in the
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@code{SwrContext} options or using the @file{libavutil/opt.h} API for
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programmatic use.
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@table @option
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@item ich, in_channel_count
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Set the number of input channels. Default value is 0. Setting this
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value is not mandatory if the corresponding channel layout
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@option{in_channel_layout} is set.
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@item och, out_channel_count
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Set the number of output channels. Default value is 0. Setting this
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value is not mandatory if the corresponding channel layout
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@option{out_channel_layout} is set.
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@item uch, used_channel_count
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Set the number of used channels. Default value is 0. This option is
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only used for special remapping.
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@item isr, in_sample_rate
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Set the input sample rate. Default value is 0.
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@item osr, out_sample_rate
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Set the output sample rate. Default value is 0.
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@item isf, in_sample_fmt
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Specify the input sample format. It is set by default to @code{none}.
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@item osf, out_sample_fmt
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Specify the output sample format. It is set by default to @code{none}.
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@item tsf, internal_sample_fmt
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Set the internal sample format. Default value is @code{none}.
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@item icl, in_channel_layout
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Set the input channel layout.
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@item ocl, out_channel_layout
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Set the output channel layout.
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@item clev, center_mix_level
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Set center mix level. It is a value expressed in deciBel, and must be
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inclusively included between -32 and +32.
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@item slev, surround_mix_level
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Set surround mix level. It is a value expressed in deciBel, and must
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be inclusively included between -32 and +32.
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@item lfe_mix_evel
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Set LFE mix level.
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@item rmvol, rematrix_volume
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Set rematrix volume. Default value is 1.0.
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@item flags, swr_flags
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Set flags used by the converter. Default value is 0.
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It supports the following individual flags:
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@table @option
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@item res
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force resampling
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@end table
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@item dither_scale
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Set the dither scale. Default value is 1.
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@item dither_method
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Set dither method. Default value is 0.
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Supported values:
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@table @samp
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@item rectangular
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select rectangular dither
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@item triangular
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select triangular dither
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@item triangular_hp
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select triangular dither with high pass
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@end table
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@item resampler
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Set resampling engine. Default value is swr.
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Supported values:
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@table @samp
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@item swr
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select the native SW Resampler; filter options precision and cheby are not
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applicable in this case.
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@item soxr
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select the SoX Resampler (where available); compensation, and filter options
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filter_size, phase_shift, filter_type & kaiser_beta, are not applicable in this
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case.
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@end table
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@item filter_size
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For swr only, set resampling filter size, default value is 32.
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@item phase_shift
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For swr only, set resampling phase shift, default value is 10, must be included
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between 0 and 30.
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@item linear_interp
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Use Linear Interpolation if set to 1, default value is 0.
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@item cutoff
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Set cutoff frequency (swr: 6dB point; soxr: 0dB point) ratio; must be a float
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value between 0 and 1. Default value is 0.97 with swr, and 0.91 with soxr
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(which, with a sample-rate of 44100, preserves the entire audio band to 20kHz).
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@item precision
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For soxr only, the precision in bits to which the resampled signal will be
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calculated. The default value of 20 (which, with suitable dithering, is
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appropriate for a destination bit-depth of 16) gives SoX's 'High Quality'; a
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value of 28 gives SoX's 'Very High Quality'.
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@item cheby
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For soxr only, selects passband rolloff none (Chebyshev) & higher-precision
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approximation for 'irrational' ratios. Default value is 0.
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@item min_comp
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For swr only, set the minimum difference between timestamps and audio data (in
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seconds) to trigger stretching/squeezing/filling or trimming of the
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data to make it match the timestamps. The default is that
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stretching/squeezing/filling and trimming is disabled
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(@option{min_comp} = @code{FLT_MAX}).
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@item min_hard_comp
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For swr only, set the minimum difference between timestamps and audio data (in
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seconds) to trigger adding/dropping samples to make it match the
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timestamps. This option effectively is a threshold to select between
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hard (trim/fill) and soft (squeeze/stretch) compensation. Note that
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all compensation is by default disabled through @option{min_comp}.
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The default is 0.1.
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@item comp_duration
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For swr only, set duration (in seconds) over which data is stretched/squeezed
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to make it match the timestamps. Must be a non-negative double float value,
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default value is 1.0.
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@item max_soft_comp
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For swr only, set maximum factor by which data is stretched/squeezed to make it
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match the timestamps. Must be a non-negative double float value, default value
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is 0.
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@item matrix_encoding
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Select matrixed stereo encoding.
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It accepts the following values:
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@table @samp
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@item none
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select none
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@item dolby
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select Dolby
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@item dplii
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select Dolby Pro Logic II
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@end table
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Default value is @code{none}.
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@item filter_type
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For swr only, select resampling filter type. This only affects resampling
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operations.
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It accepts the following values:
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@table @samp
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@item cubic
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select cubic
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@item blackman_nuttall
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select Blackman Nuttall Windowed Sinc
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@item kaiser
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select Kaiser Windowed Sinc
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@end table
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@item kaiser_beta
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For swr only, set Kaiser Window Beta value. Must be an integer included between
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2 and 16, default value is 9.
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@end table
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@c man end RESAMPLER OPTIONS
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@chapter See Also
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@ifhtml
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@url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
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@url{libswresample.html,libswresample}
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@end ifhtml
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@ifnothtml
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ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), libswresample(3)
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@end ifnothtml
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@include authors.texi
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@ignore
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@setfilename ffmpeg-resampler
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@settitle FFmpeg Resampler
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@end ignore
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@bye
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