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Stefano Sabatini
12 years ago
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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 input 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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This will automatically be chosen when it is not explicitly set. |
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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 the center mix level. It is a value expressed in deciBel, and must be |
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in the interval [-32,32]. |
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@item slev, surround_mix_level |
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Set the surround mix level. It is a value expressed in deciBel, and must |
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be in the interval [-32,32]. |
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@item lfe_mix_level |
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Set LFE mix into non LFE level. It is used when there is a LFE input but no |
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LFE output. It is a value expressed in deciBel, and must |
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be in the interval [-32,32]. |
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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, this flag forces resampling to be used even when the |
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input and output sample rates match. |
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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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@item lipshitz |
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select lipshitz noise shaping dither |
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@item shibata |
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select shibata noise shaping dither |
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@item low_shibata |
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select low shibata noise shaping dither |
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@item high_shibata |
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select high shibata noise shaping dither |
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@item f_weighted |
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select f-weighted noise shaping dither |
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@item modified_e_weighted |
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select modified-e-weighted noise shaping dither |
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@item improved_e_weighted |
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select improved-e-weighted noise shaping dither |
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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, and must be in |
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the interval [0,30]. |
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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 async |
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For swr only, simple 1 parameter audio sync to timestamps using stretching, |
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squeezing, filling and trimming. Setting this to 1 will enable filling and |
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trimming, larger values represent the maximum amount in samples that the data |
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may be stretched or squeezed for each second. |
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Default value is 0, thus no compensation is applied to make the samples match |
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the audio timestamps. |
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@item first_pts |
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For swr only, assume the first pts should be this value. The time unit is 1 / sample rate. |
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This allows for padding/trimming at the start of stream. By default, no |
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assumption is made about the first frame's expected pts, so no padding or |
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trimming is done. For example, this could be set to 0 to pad the beginning with |
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silence if an audio stream starts after the video stream or to trim any samples |
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with a negative pts due to encoder delay. |
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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 in the |
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interval [2,16], default value is 9. |
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@end table |
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@c man end RESAMPLER OPTIONS |
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