---
title: MediaSource.duration
slug: Web/API/MediaSource/duration
translation_of: Web/API/MediaSource/duration
---
<div>{{APIRef("Media Source Extensions")}}{{SeeCompatTable}}</div>

<p>{{domxref("MediaSource")}} 介面的 <code><strong>duration</strong></code> 屬性用來取得以及設置正被表示的媒體時間長度。</p>

<h2 id="語法">語法</h2>

<pre class="brush: js">mediaSource.duration = 5.5; // 5.5 seconds

var myDuration = mediaSource.duration;</pre>

<h3 id="回傳值">回傳值</h3>

<p>單位為秒的 double 型別。</p>

<h3 id="錯誤">錯誤</h3>

<p>當設置此屬性一個新的值時以下錯誤可能發生。</p>

<table class="standard-table">
 <thead>
  <tr>
   <th scope="col">錯誤</th>
   <th scope="col">解釋</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td><code>InvalidAccessError</code></td>
   <td>嘗試設置的時間長度是負值，或者 <code>NaN</code>。</td>
  </tr>
  <tr>
   <td><code>InvalidStateError</code></td>
   <td>{{domxref("MediaSource.readyState")}} 不是 <code>open</code>，或者 {{domxref("MediaSource.sourceBuffers")}} 中一個或多個以上的 {{domxref("SourceBuffer")}} 物件正在被更新（例如：他們的 {{domxref("SourceBuffer.updating")}} 屬性為 <code>true</code>。）</td>
  </tr>
 </tbody>
</table>

<h2 id="範例">範例</h2>

<p>以下的片段基於 Nick Desaulniers 所編纂的簡單範例（<a href="http://nickdesaulniers.github.io/netfix/demo/bufferAll.html">觀看實際演示</a>，或者<a href="https://github.com/nickdesaulniers/netfix/blob/gh-pages/demo/bufferAll.html">下載原始碼</a>以利更進一步研究。）</p>

<pre class="brush: js  language-js"><code class="language-js"><span class="keyword token">function</span> sourceOpen <span class="punctuation token">(</span>_<span class="punctuation token">)</span> <span class="punctuation token">{</span>
 <span class="comment token"> //console.log(this.readyState); // open
</span>  <span class="keyword token">var</span> mediaSource <span class="operator token">=</span> <span class="keyword token">this</span><span class="punctuation token">;</span>
  <span class="keyword token">var</span> sourceBuffer <span class="operator token">=</span> mediaSource<span class="punctuation token">.</span><span class="function token">addSourceBuffer<span class="punctuation token">(</span></span>mimeCodec<span class="punctuation token">)</span><span class="punctuation token">;</span>
  <span class="function token">fetchAB<span class="punctuation token">(</span></span>assetURL<span class="punctuation token">,</span> <span class="keyword token">function</span> <span class="punctuation token">(</span>buf<span class="punctuation token">)</span> <span class="punctuation token">{</span>
    sourceBuffer<span class="punctuation token">.</span><span class="function token">addEventListener<span class="punctuation token">(</span></span><span class="string token">'updateend'</span><span class="punctuation token">,</span> <span class="keyword token">function</span> <span class="punctuation token">(</span>_<span class="punctuation token">)</span> <span class="punctuation token">{</span>
      mediaSource<span class="punctuation token">.</span><span class="function token">endOfStream<span class="punctuation token">(</span></span><span class="punctuation token">)</span><span class="punctuation token">;
      mediaSource.duration = 120;</span>
      video<span class="punctuation token">.</span><span class="function token">play<span class="punctuation token">(</span></span><span class="punctuation token">)</span><span class="punctuation token">;</span>
     <span class="comment token"> //console.log(mediaSource.readyState); // ended
</span>    <span class="punctuation token">}</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
    sourceBuffer<span class="punctuation token">.</span><span class="function token">appendBuffer<span class="punctuation token">(</span></span>buf<span class="punctuation token">)</span><span class="punctuation token">;</span>
  <span class="punctuation token">}</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span><span class="punctuation token">;

...</span></code></pre>

<h2 id="規格">規格</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">規格</th>
   <th scope="col">狀態</th>
   <th scope="col">注釋</th>
  </tr>
  <tr>
   <td>{{SpecName('Media Source Extensions', '#widl-MediaSource-duration', 'duration')}}</td>
   <td>{{Spec2('Media Source Extensions')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="相容性表格">相容性表格</h2>

<div>{{CompatibilityTable}}</div>

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Edge</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari (WebKit)</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>23</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatGeckoDesktop("25.0")}}<sup>[1]</sup><br>
    {{CompatGeckoDesktop("42.0")}}</td>
   <td>11<sup>[2]</sup></td>
   <td>15</td>
   <td>8</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Edge</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>Firefox OS (Gecko)</th>
   <th>IE Phone</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>4.4.4</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>
    <p>{{CompatNo}}</p>
   </td>
   <td>{{CompatNo}}</td>
   <td>11</td>
   <td>30</td>
   <td>{{CompatNo}}</td>
  </tr>
 </tbody>
</table>
</div>

<p>[1] 在切換 <code>about:config</code> 偏好設定 <code>media.mediasource.enabled</code> 為 <code>true</code>時可以使用。此外，支援只限於白名單內的網站，如：YouTube, Netflix, 以及其他熱門的串流網站。白名單已經被移除且 Media Source Extensions 在 42+ 對所有網站已預設為啟用。</p>

<p>[2] 只在 Windows 8+ 上有效。</p>

<h2 id="相關資料">相關資料</h2>

<ul>
 <li>{{domxref("SourceBuffer")}}</li>
 <li>{{domxref("SourceBufferList")}}</li>
</ul>