1 \input texinfo @c -*- texinfo -*-
3 @settitle FFmpeg Resampler Documentation
5 @center @titlefont{FFmpeg Resampler Documentation}
13 @c man begin DESCRIPTION
15 The FFmpeg resampler provides an high-level interface to the
16 libswresample library audio resampling utilities. In particular it
17 allows to perform audio resampling, audio channel layout rematrixing,
18 and convert audio format and packing layout.
20 @c man end DESCRIPTION
22 @chapter Resampler Options
23 @c man begin RESAMPLER OPTIONS
25 The audio resampler supports the following named options.
27 Options may be set by specifying -@var{option} @var{value} in the
28 FFmpeg tools, @var{option}=@var{value} for the aresample filter,
29 by setting the value explicitly in the
30 @code{SwrContext} options or using the @file{libavutil/opt.h} API for
35 @item ich, in_channel_count
36 Set the number of input channels. Default value is 0. Setting this
37 value is not mandatory if the corresponding channel layout
38 @option{in_channel_layout} is set.
40 @item och, out_channel_count
41 Set the number of output channels. Default value is 0. Setting this
42 value is not mandatory if the corresponding channel layout
43 @option{out_channel_layout} is set.
45 @item uch, used_channel_count
46 Set the number of used input channels. Default value is 0. This option is
47 only used for special remapping.
49 @item isr, in_sample_rate
50 Set the input sample rate. Default value is 0.
52 @item osr, out_sample_rate
53 Set the output sample rate. Default value is 0.
55 @item isf, in_sample_fmt
56 Specify the input sample format. It is set by default to @code{none}.
58 @item osf, out_sample_fmt
59 Specify the output sample format. It is set by default to @code{none}.
61 @item tsf, internal_sample_fmt
62 Set the internal sample format. Default value is @code{none}.
63 This will automatically be choosen when its not explicitly set.
65 @item icl, in_channel_layout
66 Set the input channel layout.
68 @item ocl, out_channel_layout
69 Set the output channel layout.
71 @item clev, center_mix_level
72 Set the center mix level. It is a value expressed in deciBel, and must be
73 in the interval [-32,32].
75 @item slev, surround_mix_level
76 Set the surround mix level. It is a value expressed in deciBel, and must
77 be in the interval [-32,32].
80 Set LFE mix into non LFE level. It is used when there is a LFE input but no
81 LFE output. It is a value expressed in deciBel, and must
82 be in the interval [-32,32].
84 @item rmvol, rematrix_volume
85 Set rematrix volume. Default value is 1.0.
87 @item flags, swr_flags
88 Set flags used by the converter. Default value is 0.
90 It supports the following individual flags:
93 force resampling, this flag forces resampling to be used even when the
94 input and output sample rates match.
98 Set the dither scale. Default value is 1.
101 Set dither method. Default value is 0.
106 select rectangular dither
108 select triangular dither
110 select triangular dither with high pass
112 select lipshitz noise shaping dither
114 select shibata noise shaping dither
116 select low shibata noise shaping dither
118 select high shibata noise shaping dither
120 select f-weighted noise shaping dither
121 @item modified_e_weighted
122 select modified-e-weighted noise shaping dither
123 @item improved_e_weighted
124 select improved-e-weighted noise shaping dither
129 Set resampling engine. Default value is swr.
134 select the native SW Resampler; filter options precision and cheby are not
135 applicable in this case.
137 select the SoX Resampler (where available); compensation, and filter options
138 filter_size, phase_shift, filter_type & kaiser_beta, are not applicable in this
143 For swr only, set resampling filter size, default value is 32.
146 For swr only, set resampling phase shift, default value is 10, and must be in
150 Use Linear Interpolation if set to 1, default value is 0.
153 Set cutoff frequency (swr: 6dB point; soxr: 0dB point) ratio; must be a float
154 value between 0 and 1. Default value is 0.97 with swr, and 0.91 with soxr
155 (which, with a sample-rate of 44100, preserves the entire audio band to 20kHz).
158 For soxr only, the precision in bits to which the resampled signal will be
159 calculated. The default value of 20 (which, with suitable dithering, is
160 appropriate for a destination bit-depth of 16) gives SoX's 'High Quality'; a
161 value of 28 gives SoX's 'Very High Quality'.
164 For soxr only, selects passband rolloff none (Chebyshev) & higher-precision
165 approximation for 'irrational' ratios. Default value is 0.
168 For swr only, simple 1 parameter audio sync to timestamps using stretching,
169 squeezing, filling and trimming. Setting this to 1 will enable filling and
170 trimming, larger values represent the maximum amount in samples that the data
171 may be stretched or squeezed for each second.
172 Default value is 0, thus no compensation is applied to make the samples match
173 the audio timestamps.
176 For swr only, assume the first pts should be this value. The time unit is 1 / sample rate.
177 This allows for padding/trimming at the start of stream. By default, no
178 assumption is made about the first frame's expected pts, so no padding or
179 trimming is done. For example, this could be set to 0 to pad the beginning with
180 silence if an audio stream starts after the video stream or to trim any samples
181 with a negative pts due to encoder delay.
184 For swr only, set the minimum difference between timestamps and audio data (in
185 seconds) to trigger stretching/squeezing/filling or trimming of the
186 data to make it match the timestamps. The default is that
187 stretching/squeezing/filling and trimming is disabled
188 (@option{min_comp} = @code{FLT_MAX}).
191 For swr only, set the minimum difference between timestamps and audio data (in
192 seconds) to trigger adding/dropping samples to make it match the
193 timestamps. This option effectively is a threshold to select between
194 hard (trim/fill) and soft (squeeze/stretch) compensation. Note that
195 all compensation is by default disabled through @option{min_comp}.
199 For swr only, set duration (in seconds) over which data is stretched/squeezed
200 to make it match the timestamps. Must be a non-negative double float value,
201 default value is 1.0.
204 For swr only, set maximum factor by which data is stretched/squeezed to make it
205 match the timestamps. Must be a non-negative double float value, default value
208 @item matrix_encoding
209 Select matrixed stereo encoding.
211 It accepts the following values:
218 select Dolby Pro Logic II
221 Default value is @code{none}.
224 For swr only, select resampling filter type. This only affects resampling
227 It accepts the following values:
231 @item blackman_nuttall
232 select Blackman Nuttall Windowed Sinc
234 select Kaiser Windowed Sinc
238 For swr only, set Kaiser Window Beta value. Must be an integer in the
239 interval [2,16], default value is 9.
243 @c man end RESAMPLER OPTIONS
248 @url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
249 @url{libswresample.html,libswresample}
253 ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), libswresample(3)
256 @include authors.texi
260 @setfilename ffmpeg-resampler
261 @settitle FFmpeg Resampler