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<section id="module-audioop">
<span id="audioop-manipulate-raw-audio-data"></span><h1><a class="reference internal" href="#module-audioop" title="audioop: Manipulate raw audio data."><code class="xref py py-mod docutils literal notranslate"><span class="pre">audioop</span></code></a> --- 处理原始音频数据<a class="headerlink" href="#module-audioop" title="永久链接至标题"></a></h1>
<hr class="docutils" />
<p><a class="reference internal" href="#module-audioop" title="audioop: Manipulate raw audio data."><code class="xref py py-mod docutils literal notranslate"><span class="pre">audioop</span></code></a> 模块包含针对声音片段的一些有用操作。它操作的声音片段由 8、16、24 或 32 位宽的有符号整型样本组成，存储在 <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">类字节串对象</span></a> 中。除非特别说明，否则所有标量项目均为整数。</p>
<div class="versionchanged">
<p><span class="versionmodified changed">在 3.4 版更改: </span>增加了对 24 位样本的支持。现在，所有函数都接受任何 <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">类字节串对象</span></a>。而传入字符串会立即导致错误。</p>
</div>
<p id="index-0">本模块提供对 a-LAW、u-LAW 和 Intel/DVI ADPCM 编码的支持。</p>
<p>部分更复杂的操作仅接受 16 位样本，而其他操作始终需要样本大小（以字节为单位）作为该操作的参数。</p>
<p>此模块定义了下列变量和函数：</p>
<dl class="exception">
<dt id="audioop.error">
<em class="property">exception </em><code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">error</code><a class="headerlink" href="#audioop.error" title="永久链接至目标"></a></dt>
<dd><p>所有错误都会抛出此异常，比如样本的字节数未知等等。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.add">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">add</code><span class="sig-paren">(</span><em class="sig-param">fragment1</em>, <em class="sig-param">fragment2</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.add" title="永久链接至目标"></a></dt>
<dd><p>两个样本作为参数传入，返回一个片段，该片段是两个样本的和。<em>width</em> 是样本宽度（以字节为单位），可以取 <code class="docutils literal notranslate"><span class="pre">1</span></code>, <code class="docutils literal notranslate"><span class="pre">2</span></code>, <code class="docutils literal notranslate"><span class="pre">3</span></code> 或 <code class="docutils literal notranslate"><span class="pre">4</span></code>。两个片段的长度应相同。如果发生溢出，较长的样本将被截断。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.adpcm2lin">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">adpcm2lin</code><span class="sig-paren">(</span><em class="sig-param">adpcmfragment</em>, <em class="sig-param">width</em>, <em class="sig-param">state</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.adpcm2lin" title="永久链接至目标"></a></dt>
<dd><p>将 Intel/DVI ADPCM 编码的片段解码为线性片段。关于 ADPCM 编码的详情请参阅 <a class="reference internal" href="#audioop.lin2adpcm" title="audioop.lin2adpcm"><code class="xref py py-func docutils literal notranslate"><span class="pre">lin2adpcm()</span></code></a> 的描述。返回一个元组 <code class="docutils literal notranslate"><span class="pre">(sample,</span> <span class="pre">newstate)</span></code>，其中 sample 的位宽由 <em>width</em> 指定。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.alaw2lin">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">alaw2lin</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.alaw2lin" title="永久链接至目标"></a></dt>
<dd><p>将 a-LAW 编码的声音片段转换为线性编码声音片段。由于 a-LAW 编码样本始终为 8 位，因此这里的 <em>width</em> 仅指输出片段的样本位宽。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.avg">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">avg</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.avg" title="永久链接至目标"></a></dt>
<dd><p>返回片段中所有样本的平均值。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.avgpp">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">avgpp</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.avgpp" title="永久链接至目标"></a></dt>
<dd><p>返回片段中所有样本的平均峰峰值。由于没有进行过滤，因此该例程的实用性尚存疑。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.bias">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">bias</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em>, <em class="sig-param">bias</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.bias" title="永久链接至目标"></a></dt>
<dd><p>返回一个片段，该片段由原始片段中的每个样本加上偏差组成。在溢出时样本会回卷 (wrap around)。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.byteswap">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">byteswap</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.byteswap" title="永久链接至目标"></a></dt>
<dd><p>“按字节交换”片段中的所有样本，返回修改后的片段。将大端序样本转换为小端序样本，反之亦然。</p>
<div class="versionadded">
<p><span class="versionmodified added">3.4 新版功能.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="audioop.cross">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">cross</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.cross" title="永久链接至目标"></a></dt>
<dd><p>将片段作为参数传入，返回其中过零点的数量。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.findfactor">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">findfactor</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">reference</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.findfactor" title="永久链接至目标"></a></dt>
<dd><p>返回一个系数 <em>F</em> 使得 <code class="docutils literal notranslate"><span class="pre">rms(add(fragment,</span> <span class="pre">mul(reference,</span> <span class="pre">-F)))</span></code> 最小，即返回乘以 <em>reference</em> 后最匹配 <em>fragment</em> 的那个乘数。两个片段都应包含 2 字节宽的样本。</p>
<p>本例程所需的时间与 <code class="docutils literal notranslate"><span class="pre">len(fragment)</span></code> 成正比。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.findfit">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">findfit</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">reference</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.findfit" title="永久链接至目标"></a></dt>
<dd><p>尽可能尝试让 <em>reference</em> 匹配 <em>fragment</em> 的一部分（<em>fragment</em> 应较长）。从概念上讲，完成这些靠从 <em>fragment</em> 中取出切片，使用 <a class="reference internal" href="#audioop.findfactor" title="audioop.findfactor"><code class="xref py py-func docutils literal notranslate"><span class="pre">findfactor()</span></code></a> 计算最佳匹配，并最小化结果。两个片段都应包含 2 字节宽的样本。返回一个元组 <code class="docutils literal notranslate"><span class="pre">(offset,</span> <span class="pre">factor)</span></code>，其中 <em>offset</em> 是在 <em>fragment</em> 中的偏移量（整数），表示从此处开始最佳匹配，而 <em>factor</em> 是由 <a class="reference internal" href="#audioop.findfactor" title="audioop.findfactor"><code class="xref py py-func docutils literal notranslate"><span class="pre">findfactor()</span></code></a> 定义的因数（浮点数）。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.findmax">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">findmax</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">length</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.findmax" title="永久链接至目标"></a></dt>
<dd><p>在 <em>fragment</em> 中搜索所有长度为 <em>length</em> 的样本切片（不是字节！）中，能量最大的那一个切片，即返回 <em>i</em> 使得 <code class="docutils literal notranslate"><span class="pre">rms(fragment[i*2:(i+length)*2])</span></code> 最大。两个片段都应包含 2 字节宽的样本。</p>
<p>本例程所需的时间与 <code class="docutils literal notranslate"><span class="pre">len(fragment)</span></code> 成正比。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.getsample">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">getsample</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em>, <em class="sig-param">index</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.getsample" title="永久链接至目标"></a></dt>
<dd><p>返回片段中样本索引 <em>index</em> 的值。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.lin2adpcm">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">lin2adpcm</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em>, <em class="sig-param">state</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.lin2adpcm" title="永久链接至目标"></a></dt>
<dd><p>将样本转换为 4 位 Intel/DVI ADPCM 编码。ADPCM 编码是一种自适应编码方案，其中每个 4 比特数字是一个采样值与下一个采样值之间的差除以（不定的）步长。IMA 已选择使用 Intel/DVI ADPCM 算法，因此它很可能成为标准。</p>
<p><em>state</em> 是一个表示编码器状态的元组。编码器返回一个元组 <code class="docutils literal notranslate"><span class="pre">(adpcmfrag,</span> <span class="pre">newstate)</span></code>，而 <em>newstate</em> 要在下一次调用 <a class="reference internal" href="#audioop.lin2adpcm" title="audioop.lin2adpcm"><code class="xref py py-func docutils literal notranslate"><span class="pre">lin2adpcm()</span></code></a> 时传入。在初始调用中，可以将 <code class="docutils literal notranslate"><span class="pre">None</span></code> 作为 state 传递。<em>adpcmfrag</em> 是 ADPCM 编码的片段，每个字节打包了 2 个 4 比特值。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.lin2alaw">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">lin2alaw</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.lin2alaw" title="永久链接至目标"></a></dt>
<dd><p>将音频片段中的采样值转换为 a-LAW 编码，并将其作为字节对象返回。a-LAW 是一种音频编码格式，仅使用 8 位样本即可获得大约 13 位的动态范围。Sun 音频硬件等使用该编码。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.lin2lin">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">lin2lin</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em>, <em class="sig-param">newwidth</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.lin2lin" title="永久链接至目标"></a></dt>
<dd><p>将采样在 1、2、3 和 4 字节格式之间转换。</p>
<div class="admonition note">
<p class="admonition-title">注解</p>
<p>在某些音频格式（如 .WAV 文件）中，16、24 和 32 位采样是有符号的，但 8 位采样是无符号的。因此，当将这些格式转换为 8 位宽采样时，还需使结果加上 128:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">new_frames</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">lin2lin</span><span class="p">(</span><span class="n">frames</span><span class="p">,</span> <span class="n">old_width</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="n">new_frames</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">bias</span><span class="p">(</span><span class="n">new_frames</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">128</span><span class="p">)</span>
</pre></div>
</div>
<p>反之，将 8 位宽的采样转换为 16、24 或 32 位时，必须采用相同的处理。</p>
</div>
</dd></dl>
<dl class="function">
<dt id="audioop.lin2ulaw">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">lin2ulaw</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.lin2ulaw" title="永久链接至目标"></a></dt>
<dd><p>将音频片段中的采样值转换为 u-LAW 编码，并将其作为字节对象返回。u-LAW 是一种音频编码格式，仅使用 8 位采样即可获得大约 14 位的动态范围。Sun 音频硬件等使用该编码。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.max">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">max</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.max" title="永久链接至目标"></a></dt>
<dd><p>返回片段中所有采样值的最大 <em>绝对值</em>。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.maxpp">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">maxpp</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.maxpp" title="永久链接至目标"></a></dt>
<dd><p>返回声音片段中的最大峰峰值。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.minmax">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">minmax</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.minmax" title="永久链接至目标"></a></dt>
<dd><p>返回声音片段中所有采样值的最小值和最大值组成的元组。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.mul">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">mul</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em>, <em class="sig-param">factor</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.mul" title="永久链接至目标"></a></dt>
<dd><p>返回一个片段，该片段由原始片段中的每个采样值乘以浮点值 <em>factor</em> 组成。如果发生溢出，采样将被截断。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.ratecv">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">ratecv</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em>, <em class="sig-param">nchannels</em>, <em class="sig-param">inrate</em>, <em class="sig-param">outrate</em>, <em class="sig-param">state</em><span class="optional">[</span>, <em class="sig-param">weightA</em><span class="optional">[</span>, <em class="sig-param">weightB</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#audioop.ratecv" title="永久链接至目标"></a></dt>
<dd><p>转换输入片段的帧速率。</p>
<p><em>state</em> 是一个表示转换器状态的元组。转换器返回一个元组 <code class="docutils literal notranslate"><span class="pre">(newfragment,</span> <span class="pre">newstate)</span></code>，而 <em>newstate</em> 要在下一次调用 <a class="reference internal" href="#audioop.ratecv" title="audioop.ratecv"><code class="xref py py-func docutils literal notranslate"><span class="pre">ratecv()</span></code></a> 时传入。初始调用应传入 <code class="docutils literal notranslate"><span class="pre">None</span></code> 作为 state。</p>
<p>参数 <em>weightA</em> 和 <em>weightB</em> 是简单数字滤波器的参数，默认分别为 <code class="docutils literal notranslate"><span class="pre">1</span></code> 和 <code class="docutils literal notranslate"><span class="pre">0</span></code>。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.reverse">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">reverse</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.reverse" title="永久链接至目标"></a></dt>
<dd><p>将片段中的采样值反转，返回修改后的片段。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.rms">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">rms</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.rms" title="永久链接至目标"></a></dt>
<dd><p>返回片段的均方根值，即 <code class="docutils literal notranslate"><span class="pre">sqrt(sum(S_i^2)/n)</span></code>。</p>
<p>测量音频信号的能量。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.tomono">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">tomono</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em>, <em class="sig-param">lfactor</em>, <em class="sig-param">rfactor</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.tomono" title="永久链接至目标"></a></dt>
<dd><p>将立体声片段转换为单声道片段。左通道乘以 <em>lfactor</em>，右通道乘以 <em>rfactor</em>，然后两个通道相加得到单声道信号。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.tostereo">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">tostereo</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em>, <em class="sig-param">lfactor</em>, <em class="sig-param">rfactor</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.tostereo" title="永久链接至目标"></a></dt>
<dd><p>由单声道片段生成立体声片段。立体声片段中的两对采样都是从单声道计算而来的，即左声道是乘以 <em>lfactor</em>，右声道是乘以 <em>rfactor</em>。</p>
</dd></dl>
<dl class="function">
<dt id="audioop.ulaw2lin">
<code class="sig-prename descclassname">audioop.</code><code class="sig-name descname">ulaw2lin</code><span class="sig-paren">(</span><em class="sig-param">fragment</em>, <em class="sig-param">width</em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.ulaw2lin" title="永久链接至目标"></a></dt>
<dd><p>将 u-LAW 编码的声音片段转换为线性编码声音片段。由于 u-LAW 编码采样值始终为 8 位，因此这里的 <em>width</em> 仅指输出片段的采样位宽。</p>
</dd></dl>
<p>请注意，诸如 <a class="reference internal" href="#audioop.mul" title="audioop.mul"><code class="xref py py-func docutils literal notranslate"><span class="pre">mul()</span></code></a> 或 <a class="reference internal" href="#audioop.max" title="audioop.max"><code class="xref py py-func docutils literal notranslate"><span class="pre">max()</span></code></a> 之类的操作在单声道和立体声间没有区别，即所有采样都作相同处理。如果出现问题，应先将立体声片段拆分为两个单声道片段，之后再重组。以下是如何进行该操作的示例:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">mul_stereo</span><span class="p">(</span><span class="n">sample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="n">lfactor</span><span class="p">,</span> <span class="n">rfactor</span><span class="p">):</span>
<span class="n">lsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">tomono</span><span class="p">(</span><span class="n">sample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span>
<span class="n">rsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">tomono</span><span class="p">(</span><span class="n">sample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="n">lsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">mul</span><span class="p">(</span><span class="n">lsample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="n">lfactor</span><span class="p">)</span>
<span class="n">rsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">mul</span><span class="p">(</span><span class="n">rsample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="n">rfactor</span><span class="p">)</span>
<span class="n">lsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">tostereo</span><span class="p">(</span><span class="n">lsample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span>
<span class="n">rsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">tostereo</span><span class="p">(</span><span class="n">rsample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="k">return</span> <span class="n">audioop</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">lsample</span><span class="p">,</span> <span class="n">rsample</span><span class="p">,</span> <span class="n">width</span><span class="p">)</span>
</pre></div>
</div>
<p>如果使用 ADPCM 编码器构造网络数据包，并且希望协议是无状态的（即能够容忍数据包丢失），则不仅需要传输数据，还应该传输状态。请注意，必须将*初始*状态（传入 <a class="reference internal" href="#audioop.lin2adpcm" title="audioop.lin2adpcm"><code class="xref py py-func docutils literal notranslate"><span class="pre">lin2adpcm()</span></code></a> 的状态）发送给解码器，不能发送最终状态（编码器返回的状态）。如果要使用 <a class="reference internal" href="struct.html#struct.Struct" title="struct.Struct"><code class="xref py py-class docutils literal notranslate"><span class="pre">struct.Struct</span></code></a> 以二进制保存状态，可以将第一个元素（预测值）用 16 位编码，将第二个元素（增量索引）用 8 位编码。</p>
<p>本 ADPCM 编码器从不与其他 ADPCM 编码器对立，仅针对自身。本开发者可能会误读标准，这种情况下它们将无法与相应标准互操作。</p>
<p>乍看之下 <code class="xref py py-func docutils literal notranslate"><span class="pre">find*()</span></code> 例程可能有些可笑。它们主要是用于回声消除，一种快速有效的方法是选取输出样本中能量最高的片段，在输入样本中定位该片段，然后从输入样本中减去整个输出样本:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">echocancel</span><span class="p">(</span><span class="n">outputdata</span><span class="p">,</span> <span class="n">inputdata</span><span class="p">):</span>
<span class="n">pos</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">findmax</span><span class="p">(</span><span class="n">outputdata</span><span class="p">,</span> <span class="mi">800</span><span class="p">)</span> <span class="c1"># one tenth second</span>
<span class="n">out_test</span> <span class="o">=</span> <span class="n">outputdata</span><span class="p">[</span><span class="n">pos</span><span class="o">*</span><span class="mi">2</span><span class="p">:]</span>
<span class="n">in_test</span> <span class="o">=</span> <span class="n">inputdata</span><span class="p">[</span><span class="n">pos</span><span class="o">*</span><span class="mi">2</span><span class="p">:]</span>
<span class="n">ipos</span><span class="p">,</span> <span class="n">factor</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">findfit</span><span class="p">(</span><span class="n">in_test</span><span class="p">,</span> <span class="n">out_test</span><span class="p">)</span>
<span class="c1"># Optional (for better cancellation):</span>
<span class="c1"># factor = audioop.findfactor(in_test[ipos*2:ipos*2+len(out_test)],</span>
<span class="c1"># out_test)</span>
<span class="n">prefill</span> <span class="o">=</span> <span class="s1">&#39;</span><span class="se">\0</span><span class="s1">&#39;</span><span class="o">*</span><span class="p">(</span><span class="n">pos</span><span class="o">+</span><span class="n">ipos</span><span class="p">)</span><span class="o">*</span><span class="mi">2</span>
<span class="n">postfill</span> <span class="o">=</span> <span class="s1">&#39;</span><span class="se">\0</span><span class="s1">&#39;</span><span class="o">*</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">inputdata</span><span class="p">)</span><span class="o">-</span><span class="nb">len</span><span class="p">(</span><span class="n">prefill</span><span class="p">)</span><span class="o">-</span><span class="nb">len</span><span class="p">(</span><span class="n">outputdata</span><span class="p">))</span>
<span class="n">outputdata</span> <span class="o">=</span> <span class="n">prefill</span> <span class="o">+</span> <span class="n">audioop</span><span class="o">.</span><span class="n">mul</span><span class="p">(</span><span class="n">outputdata</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="o">-</span><span class="n">factor</span><span class="p">)</span> <span class="o">+</span> <span class="n">postfill</span>
<span class="k">return</span> <span class="n">audioop</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">inputdata</span><span class="p">,</span> <span class="n">outputdata</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
</pre></div>
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