1@chapter Resampler Options 2@c man begin RESAMPLER OPTIONS 3 4The audio resampler supports the following named options. 5 6Options may be set by specifying -@var{option} @var{value} in the 7FFmpeg tools, @var{option}=@var{value} for the aresample filter, 8by setting the value explicitly in the 9@code{SwrContext} options or using the @file{libavutil/opt.h} API for 10programmatic use. 11 12@table @option 13 14@item ich, in_channel_count 15Set the number of input channels. Default value is 0. Setting this 16value is not mandatory if the corresponding channel layout 17@option{in_channel_layout} is set. 18 19@item och, out_channel_count 20Set the number of output channels. Default value is 0. Setting this 21value is not mandatory if the corresponding channel layout 22@option{out_channel_layout} is set. 23 24@item uch, used_channel_count 25Set the number of used input channels. Default value is 0. This option is 26only used for special remapping. 27 28@item isr, in_sample_rate 29Set the input sample rate. Default value is 0. 30 31@item osr, out_sample_rate 32Set the output sample rate. Default value is 0. 33 34@item isf, in_sample_fmt 35Specify the input sample format. It is set by default to @code{none}. 36 37@item osf, out_sample_fmt 38Specify the output sample format. It is set by default to @code{none}. 39 40@item tsf, internal_sample_fmt 41Set the internal sample format. Default value is @code{none}. 42This will automatically be chosen when it is not explicitly set. 43 44@item icl, in_channel_layout 45@item ocl, out_channel_layout 46Set the input/output channel layout. 47 48See @ref{channel layout syntax,,the Channel Layout section in the ffmpeg-utils(1) manual,ffmpeg-utils} 49for the required syntax. 50 51@item clev, center_mix_level 52Set the center mix level. It is a value expressed in deciBel, and must be 53in the interval [-32,32]. 54 55@item slev, surround_mix_level 56Set the surround mix level. It is a value expressed in deciBel, and must 57be in the interval [-32,32]. 58 59@item lfe_mix_level 60Set LFE mix into non LFE level. It is used when there is a LFE input but no 61LFE output. It is a value expressed in deciBel, and must 62be in the interval [-32,32]. 63 64@item rmvol, rematrix_volume 65Set rematrix volume. Default value is 1.0. 66 67@item rematrix_maxval 68Set maximum output value for rematrixing. 69This can be used to prevent clipping vs. preventing volumn reduction 70A value of 1.0 prevents cliping. 71 72@item flags, swr_flags 73Set flags used by the converter. Default value is 0. 74 75It supports the following individual flags: 76@table @option 77@item res 78force resampling, this flag forces resampling to be used even when the 79input and output sample rates match. 80@end table 81 82@item dither_scale 83Set the dither scale. Default value is 1. 84 85@item dither_method 86Set dither method. Default value is 0. 87 88Supported values: 89@table @samp 90@item rectangular 91select rectangular dither 92@item triangular 93select triangular dither 94@item triangular_hp 95select triangular dither with high pass 96@item lipshitz 97select lipshitz noise shaping dither 98@item shibata 99select shibata noise shaping dither 100@item low_shibata 101select low shibata noise shaping dither 102@item high_shibata 103select high shibata noise shaping dither 104@item f_weighted 105select f-weighted noise shaping dither 106@item modified_e_weighted 107select modified-e-weighted noise shaping dither 108@item improved_e_weighted 109select improved-e-weighted noise shaping dither 110 111@end table 112 113@item resampler 114Set resampling engine. Default value is swr. 115 116Supported values: 117@table @samp 118@item swr 119select the native SW Resampler; filter options precision and cheby are not 120applicable in this case. 121@item soxr 122select the SoX Resampler (where available); compensation, and filter options 123filter_size, phase_shift, filter_type & kaiser_beta, are not applicable in this 124case. 125@end table 126 127@item filter_size 128For swr only, set resampling filter size, default value is 32. 129 130@item phase_shift 131For swr only, set resampling phase shift, default value is 10, and must be in 132the interval [0,30]. 133 134@item linear_interp 135Use Linear Interpolation if set to 1, default value is 0. 136 137@item cutoff 138Set cutoff frequency (swr: 6dB point; soxr: 0dB point) ratio; must be a float 139value between 0 and 1. Default value is 0.97 with swr, and 0.91 with soxr 140(which, with a sample-rate of 44100, preserves the entire audio band to 20kHz). 141 142@item precision 143For soxr only, the precision in bits to which the resampled signal will be 144calculated. The default value of 20 (which, with suitable dithering, is 145appropriate for a destination bit-depth of 16) gives SoX's 'High Quality'; a 146value of 28 gives SoX's 'Very High Quality'. 147 148@item cheby 149For soxr only, selects passband rolloff none (Chebyshev) & higher-precision 150approximation for 'irrational' ratios. Default value is 0. 151 152@item async 153For swr only, simple 1 parameter audio sync to timestamps using stretching, 154squeezing, filling and trimming. Setting this to 1 will enable filling and 155trimming, larger values represent the maximum amount in samples that the data 156may be stretched or squeezed for each second. 157Default value is 0, thus no compensation is applied to make the samples match 158the audio timestamps. 159 160@item first_pts 161For swr only, assume the first pts should be this value. The time unit is 1 / sample rate. 162This allows for padding/trimming at the start of stream. By default, no 163assumption is made about the first frame's expected pts, so no padding or 164trimming is done. For example, this could be set to 0 to pad the beginning with 165silence if an audio stream starts after the video stream or to trim any samples 166with a negative pts due to encoder delay. 167 168@item min_comp 169For swr only, set the minimum difference between timestamps and audio data (in 170seconds) to trigger stretching/squeezing/filling or trimming of the 171data to make it match the timestamps. The default is that 172stretching/squeezing/filling and trimming is disabled 173(@option{min_comp} = @code{FLT_MAX}). 174 175@item min_hard_comp 176For swr only, set the minimum difference between timestamps and audio data (in 177seconds) to trigger adding/dropping samples to make it match the 178timestamps. This option effectively is a threshold to select between 179hard (trim/fill) and soft (squeeze/stretch) compensation. Note that 180all compensation is by default disabled through @option{min_comp}. 181The default is 0.1. 182 183@item comp_duration 184For swr only, set duration (in seconds) over which data is stretched/squeezed 185to make it match the timestamps. Must be a non-negative double float value, 186default value is 1.0. 187 188@item max_soft_comp 189For swr only, set maximum factor by which data is stretched/squeezed to make it 190match the timestamps. Must be a non-negative double float value, default value 191is 0. 192 193@item matrix_encoding 194Select matrixed stereo encoding. 195 196It accepts the following values: 197@table @samp 198@item none 199select none 200@item dolby 201select Dolby 202@item dplii 203select Dolby Pro Logic II 204@end table 205 206Default value is @code{none}. 207 208@item filter_type 209For swr only, select resampling filter type. This only affects resampling 210operations. 211 212It accepts the following values: 213@table @samp 214@item cubic 215select cubic 216@item blackman_nuttall 217select Blackman Nuttall Windowed Sinc 218@item kaiser 219select Kaiser Windowed Sinc 220@end table 221 222@item kaiser_beta 223For swr only, set Kaiser Window Beta value. Must be an integer in the 224interval [2,16], default value is 9. 225 226@item output_sample_bits 227For swr only, set number of used output sample bits for dithering. Must be an integer in the 228interval [0,64], default value is 0, which means it's not used. 229 230@end table 231 232@c man end RESAMPLER OPTIONS 233