ffmpeg/doc/resampler.texi

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