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| FFmpeg Resampler Documentation | |
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| <h1> | |
| FFmpeg Resampler Documentation | |
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| <a name="SEC_Top"></a> | |
| <div class="element-contents" id="SEC_Contents"> | |
| <h2 class="contents-heading">Table of Contents</h2> | |
| <div class="contents"> | |
| <ul class="toc-numbered-mark"> | |
| <li><a id="toc-Description" href="#Description">1 Description</a></li> | |
| <li><a id="toc-Resampler-Options" href="#Resampler-Options">2 Resampler Options</a></li> | |
| <li><a id="toc-See-Also" href="#See-Also">3 See Also</a></li> | |
| <li><a id="toc-Authors" href="#Authors">4 Authors</a></li> | |
| </ul> | |
| </div> | |
| </div> | |
| <a name="Description"></a> | |
| <h2 class="chapter">1 Description<span class="pull-right"><a class="anchor hidden-xs" href="#Description" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Description" aria-hidden="true">TOC</a></span></h2> | |
| <p>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. | |
| </p> | |
| <a name="Resampler-Options"></a> | |
| <h2 class="chapter">2 Resampler Options<span class="pull-right"><a class="anchor hidden-xs" href="#Resampler-Options" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Resampler-Options" aria-hidden="true">TOC</a></span></h2> | |
| <p>The audio resampler supports the following named options. | |
| </p> | |
| <p>Options may be set by specifying -<var class="var">option</var> <var class="var">value</var> in the | |
| FFmpeg tools, <var class="var">option</var>=<var class="var">value</var> for the aresample filter, | |
| by setting the value explicitly in the | |
| <code class="code">SwrContext</code> options or using the <samp class="file">libavutil/opt.h</samp> API for | |
| programmatic use. | |
| </p> | |
| <dl class="table"> | |
| <dt><samp class="option">uchl, used_chlayout</samp></dt> | |
| <dd><p>Set used input channel layout. Default is unset. This option is | |
| only used for special remapping. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">isr, in_sample_rate</samp></dt> | |
| <dd><p>Set the input sample rate. Default value is 0. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">osr, out_sample_rate</samp></dt> | |
| <dd><p>Set the output sample rate. Default value is 0. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">isf, in_sample_fmt</samp></dt> | |
| <dd><p>Specify the input sample format. It is set by default to <code class="code">none</code>. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">osf, out_sample_fmt</samp></dt> | |
| <dd><p>Specify the output sample format. It is set by default to <code class="code">none</code>. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">tsf, internal_sample_fmt</samp></dt> | |
| <dd><p>Set the internal sample format. Default value is <code class="code">none</code>. | |
| This will automatically be chosen when it is not explicitly set. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">ichl, in_chlayout</samp></dt> | |
| <dt><samp class="option">ochl, out_chlayout</samp></dt> | |
| <dd><p>Set the input/output channel layout. | |
| </p> | |
| <p>See <a data-manual="ffmpeg-utils" href="ffmpeg-utils.html#channel-layout-syntax">the Channel Layout section in the ffmpeg-utils(1) manual</a> | |
| for the required syntax. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">clev, center_mix_level</samp></dt> | |
| <dd><p>Set the center mix level. It is a value expressed in deciBel, and must be | |
| in the interval [-32,32]. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">slev, surround_mix_level</samp></dt> | |
| <dd><p>Set the surround mix level. It is a value expressed in deciBel, and must | |
| be in the interval [-32,32]. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">lfe_mix_level</samp></dt> | |
| <dd><p>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]. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">rmvol, rematrix_volume</samp></dt> | |
| <dd><p>Set rematrix volume. Default value is 1.0. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">rematrix_maxval</samp></dt> | |
| <dd><p>Set maximum output value for rematrixing. | |
| This can be used to prevent clipping vs. preventing volume reduction. | |
| A value of 1.0 prevents clipping. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">flags, swr_flags</samp></dt> | |
| <dd><p>Set flags used by the converter. Default value is 0. | |
| </p> | |
| <p>It supports the following individual flags: | |
| </p><dl class="table"> | |
| <dt><samp class="option">res</samp></dt> | |
| <dd><p>force resampling, this flag forces resampling to be used even when the | |
| input and output sample rates match. | |
| </p></dd> | |
| </dl> | |
| </dd> | |
| <dt><samp class="option">dither_scale</samp></dt> | |
| <dd><p>Set the dither scale. Default value is 1. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">dither_method</samp></dt> | |
| <dd><p>Set dither method. Default value is 0. | |
| </p> | |
| <p>Supported values: | |
| </p><dl class="table"> | |
| <dt>‘<samp class="samp">rectangular</samp>’</dt> | |
| <dd><p>select rectangular dither | |
| </p></dd> | |
| <dt>‘<samp class="samp">triangular</samp>’</dt> | |
| <dd><p>select triangular dither | |
| </p></dd> | |
| <dt>‘<samp class="samp">triangular_hp</samp>’</dt> | |
| <dd><p>select triangular dither with high pass | |
| </p></dd> | |
| <dt>‘<samp class="samp">lipshitz</samp>’</dt> | |
| <dd><p>select Lipshitz noise shaping dither. | |
| </p></dd> | |
| <dt>‘<samp class="samp">shibata</samp>’</dt> | |
| <dd><p>select Shibata noise shaping dither. | |
| </p></dd> | |
| <dt>‘<samp class="samp">low_shibata</samp>’</dt> | |
| <dd><p>select low Shibata noise shaping dither. | |
| </p></dd> | |
| <dt>‘<samp class="samp">high_shibata</samp>’</dt> | |
| <dd><p>select high Shibata noise shaping dither. | |
| </p></dd> | |
| <dt>‘<samp class="samp">f_weighted</samp>’</dt> | |
| <dd><p>select f-weighted noise shaping dither | |
| </p></dd> | |
| <dt>‘<samp class="samp">modified_e_weighted</samp>’</dt> | |
| <dd><p>select modified-e-weighted noise shaping dither | |
| </p></dd> | |
| <dt>‘<samp class="samp">improved_e_weighted</samp>’</dt> | |
| <dd><p>select improved-e-weighted noise shaping dither | |
| </p> | |
| </dd> | |
| </dl> | |
| </dd> | |
| <dt><samp class="option">resampler</samp></dt> | |
| <dd><p>Set resampling engine. Default value is swr. | |
| </p> | |
| <p>Supported values: | |
| </p><dl class="table"> | |
| <dt>‘<samp class="samp">swr</samp>’</dt> | |
| <dd><p>select the native SW Resampler; filter options precision and cheby are not | |
| applicable in this case. | |
| </p></dd> | |
| <dt>‘<samp class="samp">soxr</samp>’</dt> | |
| <dd><p>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. | |
| </p></dd> | |
| </dl> | |
| </dd> | |
| <dt><samp class="option">filter_size</samp></dt> | |
| <dd><p>For swr only, set resampling filter size, default value is 32. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">phase_shift</samp></dt> | |
| <dd><p>For swr only, set resampling phase shift, default value is 10, and must be in | |
| the interval [0,30]. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">linear_interp</samp></dt> | |
| <dd><p>Use linear interpolation when enabled (the default). Disable it if you want | |
| to preserve speed instead of quality when exact_rational fails. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">exact_rational</samp></dt> | |
| <dd><p>For swr only, when enabled, try to use exact phase_count based on input and | |
| output sample rate. However, if it is larger than <code class="code">1 << phase_shift</code>, | |
| the phase_count will be <code class="code">1 << phase_shift</code> as fallback. Default is enabled. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">cutoff</samp></dt> | |
| <dd><p>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). | |
| </p> | |
| </dd> | |
| <dt><samp class="option">precision</samp></dt> | |
| <dd><p>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’. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">cheby</samp></dt> | |
| <dd><p>For soxr only, selects passband rolloff none (Chebyshev) & higher-precision | |
| approximation for ’irrational’ ratios. Default value is 0. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">async</samp></dt> | |
| <dd><p>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. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">first_pts</samp></dt> | |
| <dd><p>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. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">min_comp</samp></dt> | |
| <dd><p>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 | |
| (<samp class="option">min_comp</samp> = <code class="code">FLT_MAX</code>). | |
| </p> | |
| </dd> | |
| <dt><samp class="option">min_hard_comp</samp></dt> | |
| <dd><p>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 <samp class="option">min_comp</samp>. | |
| The default is 0.1. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">comp_duration</samp></dt> | |
| <dd><p>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. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">max_soft_comp</samp></dt> | |
| <dd><p>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. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">matrix_encoding</samp></dt> | |
| <dd><p>Select matrixed stereo encoding. | |
| </p> | |
| <p>It accepts the following values: | |
| </p><dl class="table"> | |
| <dt>‘<samp class="samp">none</samp>’</dt> | |
| <dd><p>select none | |
| </p></dd> | |
| <dt>‘<samp class="samp">dolby</samp>’</dt> | |
| <dd><p>select Dolby | |
| </p></dd> | |
| <dt>‘<samp class="samp">dplii</samp>’</dt> | |
| <dd><p>select Dolby Pro Logic II | |
| </p></dd> | |
| </dl> | |
| <p>Default value is <code class="code">none</code>. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">filter_type</samp></dt> | |
| <dd><p>For swr only, select resampling filter type. This only affects resampling | |
| operations. | |
| </p> | |
| <p>It accepts the following values: | |
| </p><dl class="table"> | |
| <dt>‘<samp class="samp">cubic</samp>’</dt> | |
| <dd><p>select cubic | |
| </p></dd> | |
| <dt>‘<samp class="samp">blackman_nuttall</samp>’</dt> | |
| <dd><p>select Blackman Nuttall windowed sinc | |
| </p></dd> | |
| <dt>‘<samp class="samp">kaiser</samp>’</dt> | |
| <dd><p>select Kaiser windowed sinc | |
| </p></dd> | |
| </dl> | |
| </dd> | |
| <dt><samp class="option">kaiser_beta</samp></dt> | |
| <dd><p>For swr only, set Kaiser window beta value. Must be a double float value in the | |
| interval [2,16], default value is 9. | |
| </p> | |
| </dd> | |
| <dt><samp class="option">output_sample_bits</samp></dt> | |
| <dd><p>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. | |
| </p> | |
| </dd> | |
| </dl> | |
| <a name="See-Also"></a> | |
| <h2 class="chapter">3 See Also<span class="pull-right"><a class="anchor hidden-xs" href="#See-Also" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-See-Also" aria-hidden="true">TOC</a></span></h2> | |
| <p><a class="url" href="ffmpeg.html">ffmpeg</a>, <a class="url" href="ffplay.html">ffplay</a>, <a class="url" href="ffprobe.html">ffprobe</a>, | |
| <a class="url" href="libswresample.html">libswresample</a> | |
| </p> | |
| <a name="Authors"></a> | |
| <h2 class="chapter">4 Authors<span class="pull-right"><a class="anchor hidden-xs" href="#Authors" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Authors" aria-hidden="true">TOC</a></span></h2> | |
| <p>The FFmpeg developers. | |
| </p> | |
| <p>For details about the authorship, see the Git history of the project | |
| (https://git.ffmpeg.org/ffmpeg), e.g. by typing the command | |
| <code class="command">git log</code> in the FFmpeg source directory, or browsing the | |
| online repository at <a class="url" href="https://git.ffmpeg.org/ffmpeg">https://git.ffmpeg.org/ffmpeg</a>. | |
| </p> | |
| <p>Maintainers for the specific components are listed in the file | |
| <samp class="file">MAINTAINERS</samp> in the source code tree. | |
| </p> | |
| <p style="font-size: small;"> | |
| This document was generated using <a class="uref" href="https://www.gnu.org/software/texinfo/"><em class="emph">makeinfo</em></a>. | |
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