| =encoding utf8 | |
| =head1 NAME | |
| ffmpeg-resampler - FFmpeg Resampler | |
| =head1 DESCRIPTION | |
| The FFmpeg resampler provides a high-level interface to the | |
| libswresample library audio resampling utilities. In particular it | |
| allows one to perform audio resampling, audio channel layout rematrixing, | |
| and convert audio format and packing layout. | |
| =head1 RESAMPLER OPTIONS | |
| The audio resampler supports the following named options. | |
| Options may be set by specifying -I<option> I<value> in the | |
| FFmpeg tools, I<option>=I<value> for the aresample filter, | |
| by setting the value explicitly in the | |
| C<SwrContext> options or using the F<libavutil/opt.h> API for | |
| programmatic use. | |
| =over 4 | |
| =item B<uchl, used_chlayout> | |
| Set used input channel layout. Default is unset. This option is | |
| only used for special remapping. | |
| =item B<isr, in_sample_rate> | |
| Set the input sample rate. Default value is 0. | |
| =item B<osr, out_sample_rate> | |
| Set the output sample rate. Default value is 0. | |
| =item B<isf, in_sample_fmt> | |
| Specify the input sample format. It is set by default to C<none>. | |
| =item B<osf, out_sample_fmt> | |
| Specify the output sample format. It is set by default to C<none>. | |
| =item B<tsf, internal_sample_fmt> | |
| Set the internal sample format. Default value is C<none>. | |
| This will automatically be chosen when it is not explicitly set. | |
| =item B<ichl, in_chlayout> | |
| =item B<ochl, out_chlayout> | |
| Set the input/output channel layout. | |
| See B<the Channel Layout section in the ffmpeg-utils(1) manual> | |
| for the required syntax. | |
| =item B<clev, center_mix_level> | |
| Set the center mix level. It is a value expressed in deciBel, and must be | |
| in the interval [-32,32]. | |
| =item B<slev, surround_mix_level> | |
| Set the surround mix level. It is a value expressed in deciBel, and must | |
| be in the interval [-32,32]. | |
| =item B<lfe_mix_level> | |
| Set LFE mix into non LFE level. It is used when there is a LFE input but no | |
| LFE output. It is a value expressed in deciBel, and must | |
| be in the interval [-32,32]. | |
| =item B<rmvol, rematrix_volume> | |
| Set rematrix volume. Default value is 1.0. | |
| =item B<rematrix_maxval> | |
| Set maximum output value for rematrixing. | |
| This can be used to prevent clipping vs. preventing volume reduction. | |
| A value of 1.0 prevents clipping. | |
| =item B<flags, swr_flags> | |
| Set flags used by the converter. Default value is 0. | |
| It supports the following individual flags: | |
| =over 4 | |
| =item B<res> | |
| force resampling, this flag forces resampling to be used even when the | |
| input and output sample rates match. | |
| =back | |
| =item B<dither_scale> | |
| Set the dither scale. Default value is 1. | |
| =item B<dither_method> | |
| Set dither method. Default value is 0. | |
| Supported values: | |
| =over 4 | |
| =item B<rectangular> | |
| select rectangular dither | |
| =item B<triangular> | |
| select triangular dither | |
| =item B<triangular_hp> | |
| select triangular dither with high pass | |
| =item B<lipshitz> | |
| select Lipshitz noise shaping dither. | |
| =item B<shibata> | |
| select Shibata noise shaping dither. | |
| =item B<low_shibata> | |
| select low Shibata noise shaping dither. | |
| =item B<high_shibata> | |
| select high Shibata noise shaping dither. | |
| =item B<f_weighted> | |
| select f-weighted noise shaping dither | |
| =item B<modified_e_weighted> | |
| select modified-e-weighted noise shaping dither | |
| =item B<improved_e_weighted> | |
| select improved-e-weighted noise shaping dither | |
| =back | |
| =item B<resampler> | |
| Set resampling engine. Default value is swr. | |
| Supported values: | |
| =over 4 | |
| =item B<swr> | |
| select the native SW Resampler; filter options precision and cheby are not | |
| applicable in this case. | |
| =item B<soxr> | |
| select the SoX Resampler (where available); compensation, and filter options | |
| filter_size, phase_shift, exact_rational, filter_type & kaiser_beta, are not | |
| applicable in this case. | |
| =back | |
| =item B<filter_size> | |
| For swr only, set resampling filter size, default value is 32. | |
| =item B<phase_shift> | |
| For swr only, set resampling phase shift, default value is 10, and must be in | |
| the interval [0,30]. | |
| =item B<linear_interp> | |
| Use linear interpolation when enabled (the default). Disable it if you want | |
| to preserve speed instead of quality when exact_rational fails. | |
| =item B<exact_rational> | |
| For swr only, when enabled, try to use exact phase_count based on input and | |
| output sample rate. However, if it is larger than C<1 E<lt>E<lt> phase_shift>, | |
| the phase_count will be C<1 E<lt>E<lt> phase_shift> as fallback. Default is enabled. | |
| =item B<cutoff> | |
| Set cutoff frequency (swr: 6dB point; soxr: 0dB point) ratio; must be a float | |
| value between 0 and 1. Default value is 0.97 with swr, and 0.91 with soxr | |
| (which, with a sample-rate of 44100, preserves the entire audio band to 20kHz). | |
| =item B<precision> | |
| For soxr only, the precision in bits to which the resampled signal will be | |
| calculated. The default value of 20 (which, with suitable dithering, is | |
| appropriate for a destination bit-depth of 16) gives SoX's 'High Quality'; a | |
| value of 28 gives SoX's 'Very High Quality'. | |
| =item B<cheby> | |
| For soxr only, selects passband rolloff none (Chebyshev) & higher-precision | |
| approximation for 'irrational' ratios. Default value is 0. | |
| =item B<async> | |
| For swr only, simple 1 parameter audio sync to timestamps using stretching, | |
| squeezing, filling and trimming. Setting this to 1 will enable filling and | |
| trimming, larger values represent the maximum amount in samples that the data | |
| may be stretched or squeezed for each second. | |
| Default value is 0, thus no compensation is applied to make the samples match | |
| the audio timestamps. | |
| =item B<first_pts> | |
| For swr only, assume the first pts should be this value. The time unit is 1 / sample rate. | |
| This allows for padding/trimming at the start of stream. By default, no | |
| assumption is made about the first frame's expected pts, so no padding or | |
| trimming is done. For example, this could be set to 0 to pad the beginning with | |
| silence if an audio stream starts after the video stream or to trim any samples | |
| with a negative pts due to encoder delay. | |
| =item B<min_comp> | |
| For swr only, set the minimum difference between timestamps and audio data (in | |
| seconds) to trigger stretching/squeezing/filling or trimming of the | |
| data to make it match the timestamps. The default is that | |
| stretching/squeezing/filling and trimming is disabled | |
| (B<min_comp> = C<FLT_MAX>). | |
| =item B<min_hard_comp> | |
| For swr only, set the minimum difference between timestamps and audio data (in | |
| seconds) to trigger adding/dropping samples to make it match the | |
| timestamps. This option effectively is a threshold to select between | |
| hard (trim/fill) and soft (squeeze/stretch) compensation. Note that | |
| all compensation is by default disabled through B<min_comp>. | |
| The default is 0.1. | |
| =item B<comp_duration> | |
| For swr only, set duration (in seconds) over which data is stretched/squeezed | |
| to make it match the timestamps. Must be a non-negative double float value, | |
| default value is 1.0. | |
| =item B<max_soft_comp> | |
| For swr only, set maximum factor by which data is stretched/squeezed to make it | |
| match the timestamps. Must be a non-negative double float value, default value | |
| is 0. | |
| =item B<matrix_encoding> | |
| Select matrixed stereo encoding. | |
| It accepts the following values: | |
| =over 4 | |
| =item B<none> | |
| select none | |
| =item B<dolby> | |
| select Dolby | |
| =item B<dplii> | |
| select Dolby Pro Logic II | |
| =back | |
| Default value is C<none>. | |
| =item B<filter_type> | |
| For swr only, select resampling filter type. This only affects resampling | |
| operations. | |
| It accepts the following values: | |
| =over 4 | |
| =item B<cubic> | |
| select cubic | |
| =item B<blackman_nuttall> | |
| select Blackman Nuttall windowed sinc | |
| =item B<kaiser> | |
| select Kaiser windowed sinc | |
| =back | |
| =item B<kaiser_beta> | |
| For swr only, set Kaiser window beta value. Must be a double float value in the | |
| interval [2,16], default value is 9. | |
| =item B<output_sample_bits> | |
| For swr only, set number of used output sample bits for dithering. Must be an integer in the | |
| interval [0,64], default value is 0, which means it's not used. | |
| =back | |
| =head1 SEE ALSO | |
| ffmpeg(1), ffplay(1), ffprobe(1), libswresample(3) | |
| =head1 AUTHORS | |
| The FFmpeg developers. | |
| For details about the authorship, see the Git history of the project | |
| (https://git.ffmpeg.org/ffmpeg), e.g. by typing the command | |
| B<git log> in the FFmpeg source directory, or browsing the | |
| online repository at E<lt>B<https://git.ffmpeg.org/ffmpeg>E<gt>. | |
| Maintainers for the specific components are listed in the file | |
| F<MAINTAINERS> in the source code tree. | |