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  29. <h1 class="titlefont">FFmpeg Resampler Documentation</h1>

  30. <hr>

  31. <a name="SEC_Top"></a>

  32. 

  33. <a name="SEC_Contents"></a>

  34. <h1>Table of Contents</h1>

  35. 

  36. <div class="contents">

  37. 

  38. <ul class="no-bullet">

  39.   <li><a name="toc-Description" href="#Description">1 Description</a></li>

  40.   <li><a name="toc-Resampler-Options" href="#Resampler-Options">2 Resampler Options</a></li>

  41.   <li><a name="toc-See-Also" href="#See-Also">3 See Also</a></li>

  42.   <li><a name="toc-Authors" href="#Authors">4 Authors</a></li>

  43. </ul>

  44. </div>

  45. 

  46. 

  47. <hr size="6">

  48. <a name="Description"></a>

  49. <h1 class="chapter"><a href="ffmpeg-resampler.html#toc-Description">1 Description</a></h1>

  50. 

  51. <p>The FFmpeg resampler provides a high-level interface to the

  52. libswresample library audio resampling utilities. In particular it

  53. allows one to perform audio resampling, audio channel layout rematrixing,

  54. and convert audio format and packing layout.

  55. </p>

  56. 

  57. <a name="Resampler-Options"></a>

  58. <h1 class="chapter"><a href="ffmpeg-resampler.html#toc-Resampler-Options">2 Resampler Options</a></h1>

  59. 

  60. <p>The audio resampler supports the following named options.

  61. </p>

  62. <p>Options may be set by specifying -<var>option</var> <var>value</var> in the

  63. FFmpeg tools, <var>option</var>=<var>value</var> for the aresample filter,

  64. by setting the value explicitly in the

  65. <code>SwrContext</code> options or using the &lsquo;<tt>libavutil/opt.h</tt>&rsquo; API for

  66. programmatic use.

  67. </p>

  68. <dl compact="compact">

  69. <dt>&lsquo;<samp>ich, in_channel_count</samp>&rsquo;</dt>

  70. <dd><p>Set the number of input channels. Default value is 0. Setting this

  71. value is not mandatory if the corresponding channel layout

  72. &lsquo;<samp>in_channel_layout</samp>&rsquo; is set.

  73. </p>

  74. </dd>

  75. <dt>&lsquo;<samp>och, out_channel_count</samp>&rsquo;</dt>

  76. <dd><p>Set the number of output channels. Default value is 0. Setting this

  77. value is not mandatory if the corresponding channel layout

  78. &lsquo;<samp>out_channel_layout</samp>&rsquo; is set.

  79. </p>

  80. </dd>

  81. <dt>&lsquo;<samp>uch, used_channel_count</samp>&rsquo;</dt>

  82. <dd><p>Set the number of used input channels. Default value is 0. This option is

  83. only used for special remapping.

  84. </p>

  85. </dd>

  86. <dt>&lsquo;<samp>isr, in_sample_rate</samp>&rsquo;</dt>

  87. <dd><p>Set the input sample rate. Default value is 0.

  88. </p>

  89. </dd>

  90. <dt>&lsquo;<samp>osr, out_sample_rate</samp>&rsquo;</dt>

  91. <dd><p>Set the output sample rate. Default value is 0.

  92. </p>

  93. </dd>

  94. <dt>&lsquo;<samp>isf, in_sample_fmt</samp>&rsquo;</dt>

  95. <dd><p>Specify the input sample format. It is set by default to <code>none</code>.

  96. </p>

  97. </dd>

  98. <dt>&lsquo;<samp>osf, out_sample_fmt</samp>&rsquo;</dt>

  99. <dd><p>Specify the output sample format. It is set by default to <code>none</code>.

  100. </p>

  101. </dd>

  102. <dt>&lsquo;<samp>tsf, internal_sample_fmt</samp>&rsquo;</dt>

  103. <dd><p>Set the internal sample format. Default value is <code>none</code>.

  104. This will automatically be chosen when it is not explicitly set.

  105. </p>

  106. </dd>

  107. <dt>&lsquo;<samp>icl, in_channel_layout</samp>&rsquo;</dt>

  108. <dt>&lsquo;<samp>ocl, out_channel_layout</samp>&rsquo;</dt>

  109. <dd><p>Set the input/output channel layout.

  110. </p>

  111. <p>See <a href="ffmpeg-utils.html#channel-layout-syntax">(ffmpeg-utils)the Channel Layout section in the ffmpeg-utils(1) manual</a>

  112. for the required syntax.

  113. </p>

  114. </dd>

  115. <dt>&lsquo;<samp>clev, center_mix_level</samp>&rsquo;</dt>

  116. <dd><p>Set the center mix level. It is a value expressed in deciBel, and must be

  117. in the interval [-32,32].

  118. </p>

  119. </dd>

  120. <dt>&lsquo;<samp>slev, surround_mix_level</samp>&rsquo;</dt>

  121. <dd><p>Set the surround mix level. It is a value expressed in deciBel, and must

  122. be in the interval [-32,32].

  123. </p>

  124. </dd>

  125. <dt>&lsquo;<samp>lfe_mix_level</samp>&rsquo;</dt>

  126. <dd><p>Set LFE mix into non LFE level. It is used when there is a LFE input but no

  127. LFE output. It is a value expressed in deciBel, and must

  128. be in the interval [-32,32].

  129. </p>

  130. </dd>

  131. <dt>&lsquo;<samp>rmvol, rematrix_volume</samp>&rsquo;</dt>

  132. <dd><p>Set rematrix volume. Default value is 1.0.

  133. </p>

  134. </dd>

  135. <dt>&lsquo;<samp>rematrix_maxval</samp>&rsquo;</dt>

  136. <dd><p>Set maximum output value for rematrixing.

  137. This can be used to prevent clipping vs. preventing volume reduction.

  138. A value of 1.0 prevents clipping.

  139. </p>

  140. </dd>

  141. <dt>&lsquo;<samp>flags, swr_flags</samp>&rsquo;</dt>

  142. <dd><p>Set flags used by the converter. Default value is 0.

  143. </p>

  144. <p>It supports the following individual flags:

  145. </p><dl compact="compact">

  146. <dt>&lsquo;<samp>res</samp>&rsquo;</dt>

  147. <dd><p>force resampling, this flag forces resampling to be used even when the

  148. input and output sample rates match.

  149. </p></dd>

  150. </dl>

  151. 

  152. </dd>

  153. <dt>&lsquo;<samp>dither_scale</samp>&rsquo;</dt>

  154. <dd><p>Set the dither scale. Default value is 1.

  155. </p>

  156. </dd>

  157. <dt>&lsquo;<samp>dither_method</samp>&rsquo;</dt>

  158. <dd><p>Set dither method. Default value is 0.

  159. </p>

  160. <p>Supported values:

  161. </p><dl compact="compact">

  162. <dt>&lsquo;<samp>rectangular</samp>&rsquo;</dt>

  163. <dd><p>select rectangular dither

  164. </p></dd>

  165. <dt>&lsquo;<samp>triangular</samp>&rsquo;</dt>

  166. <dd><p>select triangular dither

  167. </p></dd>

  168. <dt>&lsquo;<samp>triangular_hp</samp>&rsquo;</dt>

  169. <dd><p>select triangular dither with high pass

  170. </p></dd>

  171. <dt>&lsquo;<samp>lipshitz</samp>&rsquo;</dt>

  172. <dd><p>select Lipshitz noise shaping dither.

  173. </p></dd>

  174. <dt>&lsquo;<samp>shibata</samp>&rsquo;</dt>

  175. <dd><p>select Shibata noise shaping dither.

  176. </p></dd>

  177. <dt>&lsquo;<samp>low_shibata</samp>&rsquo;</dt>

  178. <dd><p>select low Shibata noise shaping dither.

  179. </p></dd>

  180. <dt>&lsquo;<samp>high_shibata</samp>&rsquo;</dt>

  181. <dd><p>select high Shibata noise shaping dither.

  182. </p></dd>

  183. <dt>&lsquo;<samp>f_weighted</samp>&rsquo;</dt>

  184. <dd><p>select f-weighted noise shaping dither

  185. </p></dd>

  186. <dt>&lsquo;<samp>modified_e_weighted</samp>&rsquo;</dt>

  187. <dd><p>select modified-e-weighted noise shaping dither

  188. </p></dd>

  189. <dt>&lsquo;<samp>improved_e_weighted</samp>&rsquo;</dt>

  190. <dd><p>select improved-e-weighted noise shaping dither

  191. </p>

  192. </dd>

  193. </dl>

  194. 

  195. </dd>

  196. <dt>&lsquo;<samp>resampler</samp>&rsquo;</dt>

  197. <dd><p>Set resampling engine. Default value is swr.

  198. </p>

  199. <p>Supported values:

  200. </p><dl compact="compact">

  201. <dt>&lsquo;<samp>swr</samp>&rsquo;</dt>

  202. <dd><p>select the native SW Resampler; filter options precision and cheby are not

  203. applicable in this case.

  204. </p></dd>

  205. <dt>&lsquo;<samp>soxr</samp>&rsquo;</dt>

  206. <dd><p>select the SoX Resampler (where available); compensation, and filter options

  207. filter_size, phase_shift, exact_rational, filter_type &amp; kaiser_beta, are not

  208. applicable in this case.

  209. </p></dd>

  210. </dl>

  211. 

  212. </dd>

  213. <dt>&lsquo;<samp>filter_size</samp>&rsquo;</dt>

  214. <dd><p>For swr only, set resampling filter size, default value is 32.

  215. </p>

  216. </dd>

  217. <dt>&lsquo;<samp>phase_shift</samp>&rsquo;</dt>

  218. <dd><p>For swr only, set resampling phase shift, default value is 10, and must be in

  219. the interval [0,30].

  220. </p>

  221. </dd>

  222. <dt>&lsquo;<samp>linear_interp</samp>&rsquo;</dt>

  223. <dd><p>Use linear interpolation when enabled (the default). Disable it if you want

  224. to preserve speed instead of quality when exact_rational fails.

  225. </p>

  226. </dd>

  227. <dt>&lsquo;<samp>exact_rational</samp>&rsquo;</dt>

  228. <dd><p>For swr only, when enabled, try to use exact phase_count based on input and

  229. output sample rate. However, if it is larger than <code>1 &lt;&lt; phase_shift</code>,

  230. the phase_count will be <code>1 &lt;&lt; phase_shift</code> as fallback. Default is enabled.

  231. </p>

  232. </dd>

  233. <dt>&lsquo;<samp>cutoff</samp>&rsquo;</dt>

  234. <dd><p>Set cutoff frequency (swr: 6dB point; soxr: 0dB point) ratio; must be a float

  235. value between 0 and 1.  Default value is 0.97 with swr, and 0.91 with soxr

  236. (which, with a sample-rate of 44100, preserves the entire audio band to 20kHz).

  237. </p>

  238. </dd>

  239. <dt>&lsquo;<samp>precision</samp>&rsquo;</dt>

  240. <dd><p>For soxr only, the precision in bits to which the resampled signal will be

  241. calculated.  The default value of 20 (which, with suitable dithering, is

  242. appropriate for a destination bit-depth of 16) gives SoX&rsquo;s &rsquo;High Quality&rsquo;; a

  243. value of 28 gives SoX&rsquo;s &rsquo;Very High Quality&rsquo;.

  244. </p>

  245. </dd>

  246. <dt>&lsquo;<samp>cheby</samp>&rsquo;</dt>

  247. <dd><p>For soxr only, selects passband rolloff none (Chebyshev) &amp; higher-precision

  248. approximation for &rsquo;irrational&rsquo; ratios. Default value is 0.

  249. </p>

  250. </dd>

  251. <dt>&lsquo;<samp>async</samp>&rsquo;</dt>

  252. <dd><p>For swr only, simple 1 parameter audio sync to timestamps using stretching,

  253. squeezing, filling and trimming. Setting this to 1 will enable filling and

  254. trimming, larger values represent the maximum amount in samples that the data

  255. may be stretched or squeezed for each second.

  256. Default value is 0, thus no compensation is applied to make the samples match

  257. the audio timestamps.

  258. </p>

  259. </dd>

  260. <dt>&lsquo;<samp>first_pts</samp>&rsquo;</dt>

  261. <dd><p>For swr only, assume the first pts should be this value. The time unit is 1 / sample rate.

  262. This allows for padding/trimming at the start of stream. By default, no

  263. assumption is made about the first frame&rsquo;s expected pts, so no padding or

  264. trimming is done. For example, this could be set to 0 to pad the beginning with

  265. silence if an audio stream starts after the video stream or to trim any samples

  266. with a negative pts due to encoder delay.

  267. </p>

  268. </dd>

  269. <dt>&lsquo;<samp>min_comp</samp>&rsquo;</dt>

  270. <dd><p>For swr only, set the minimum difference between timestamps and audio data (in

  271. seconds) to trigger stretching/squeezing/filling or trimming of the

  272. data to make it match the timestamps. The default is that

  273. stretching/squeezing/filling and trimming is disabled

  274. (&lsquo;<samp>min_comp</samp>&rsquo; = <code>FLT_MAX</code>).

  275. </p>

  276. </dd>

  277. <dt>&lsquo;<samp>min_hard_comp</samp>&rsquo;</dt>

  278. <dd><p>For swr only, set the minimum difference between timestamps and audio data (in

  279. seconds) to trigger adding/dropping samples to make it match the

  280. timestamps.  This option effectively is a threshold to select between

  281. hard (trim/fill) and soft (squeeze/stretch) compensation. Note that

  282. all compensation is by default disabled through &lsquo;<samp>min_comp</samp>&rsquo;.

  283. The default is 0.1.

  284. </p>

  285. </dd>

  286. <dt>&lsquo;<samp>comp_duration</samp>&rsquo;</dt>

  287. <dd><p>For swr only, set duration (in seconds) over which data is stretched/squeezed

  288. to make it match the timestamps. Must be a non-negative double float value,

  289. default value is 1.0.

  290. </p>

  291. </dd>

  292. <dt>&lsquo;<samp>max_soft_comp</samp>&rsquo;</dt>

  293. <dd><p>For swr only, set maximum factor by which data is stretched/squeezed to make it

  294. match the timestamps. Must be a non-negative double float value, default value

  295. is 0.

  296. </p>

  297. </dd>

  298. <dt>&lsquo;<samp>matrix_encoding</samp>&rsquo;</dt>

  299. <dd><p>Select matrixed stereo encoding.

  300. </p>

  301. <p>It accepts the following values:

  302. </p><dl compact="compact">

  303. <dt>&lsquo;<samp>none</samp>&rsquo;</dt>

  304. <dd><p>select none

  305. </p></dd>

  306. <dt>&lsquo;<samp>dolby</samp>&rsquo;</dt>

  307. <dd><p>select Dolby

  308. </p></dd>

  309. <dt>&lsquo;<samp>dplii</samp>&rsquo;</dt>

  310. <dd><p>select Dolby Pro Logic II

  311. </p></dd>

  312. </dl>

  313. 

  314. <p>Default value is <code>none</code>.

  315. </p>

  316. </dd>

  317. <dt>&lsquo;<samp>filter_type</samp>&rsquo;</dt>

  318. <dd><p>For swr only, select resampling filter type. This only affects resampling

  319. operations.

  320. </p>

  321. <p>It accepts the following values:

  322. </p><dl compact="compact">

  323. <dt>&lsquo;<samp>cubic</samp>&rsquo;</dt>

  324. <dd><p>select cubic

  325. </p></dd>

  326. <dt>&lsquo;<samp>blackman_nuttall</samp>&rsquo;</dt>

  327. <dd><p>select Blackman Nuttall windowed sinc

  328. </p></dd>

  329. <dt>&lsquo;<samp>kaiser</samp>&rsquo;</dt>

  330. <dd><p>select Kaiser windowed sinc

  331. </p></dd>

  332. </dl>

  333. 

  334. </dd>

  335. <dt>&lsquo;<samp>kaiser_beta</samp>&rsquo;</dt>

  336. <dd><p>For swr only, set Kaiser window beta value. Must be a double float value in the

  337. interval [2,16], default value is 9.

  338. </p>

  339. </dd>

  340. <dt>&lsquo;<samp>output_sample_bits</samp>&rsquo;</dt>

  341. <dd><p>For swr only, set number of used output sample bits for dithering. Must be an integer in the

  342. interval [0,64], default value is 0, which means it&rsquo;s not used.

  343. </p>

  344. </dd>

  345. </dl>

  346. 

  347. 

  348. <a name="See-Also"></a>

  349. <h1 class="chapter"><a href="ffmpeg-resampler.html#toc-See-Also">3 See Also</a></h1>

  350. 

  351. <p><a href="ffmpeg.html">ffmpeg</a>, <a href="ffplay.html">ffplay</a>, <a href="ffprobe.html">ffprobe</a>,

  352. <a href="libswresample.html">libswresample</a>

  353. </p>

  354. 

  355. <a name="Authors"></a>

  356. <h1 class="chapter"><a href="ffmpeg-resampler.html#toc-Authors">4 Authors</a></h1>

  357. 

  358. <p>The FFmpeg developers.

  359. </p>

  360. <p>For details about the authorship, see the Git history of the project

  361. (git://source.ffmpeg.org/ffmpeg), e.g. by typing the command

  362. <code>git log</code> in the FFmpeg source directory, or browsing the

  363. online repository at <a href="http://source.ffmpeg.org">http://source.ffmpeg.org</a>.

  364. </p>

  365. <p>Maintainers for the specific components are listed in the file

  366. &lsquo;<tt>MAINTAINERS</tt>&rsquo; in the source code tree.

  367. </p>

  368. 

  369.     </div>

  370.   </body>

  371. </html>