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        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - Implement WebVTT VTTCue lineAlign and positionAlign attributes"
   href="https://bugs.webkit.org/show_bug.cgi?id=168715">168715</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Implement WebVTT VTTCue lineAlign and positionAlign attributes
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>WebKit
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>Safari Technology Preview
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>Unspecified
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Unspecified
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>Normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P2
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>Media Elements
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>webkit-unassigned&#64;lists.webkit.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>zcorpan&#64;gmail.com
          </td>
        </tr></table>
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        <pre>VTTCue.lineAlign and VTTCue.positionAlign are not supported.

In the WebVTT syntax these are specified after a &quot;,&quot; in position and line settings.

Spec:
<a href="http://w3c.github.io/webvtt/#webvtt-cue-position-alignment">http://w3c.github.io/webvtt/#webvtt-cue-position-alignment</a>
<a href="http://w3c.github.io/webvtt/#webvtt-cue-line-alignment">http://w3c.github.io/webvtt/#webvtt-cue-line-alignment</a>
<a href="http://w3c.github.io/webvtt/#parse-the-webvtt-cue-settings">http://w3c.github.io/webvtt/#parse-the-webvtt-cue-settings</a>
<a href="http://w3c.github.io/webvtt/#the-vttcue-interface">http://w3c.github.io/webvtt/#the-vttcue-interface</a>

Tests:
<a href="http://w3c-test.org/webvtt/api/VTTCue/lineAlign.html">http://w3c-test.org/webvtt/api/VTTCue/lineAlign.html</a>
<a href="http://w3c-test.org/webvtt/api/VTTCue/positionAlign.html">http://w3c-test.org/webvtt/api/VTTCue/positionAlign.html</a>

These are supported in Gecko. Bug for Chromium: <a href="https://bugs.chromium.org/p/chromium/issues/detail?id=633690">https://bugs.chromium.org/p/chromium/issues/detail?id=633690</a>

I think the use case is basically better control in positioning things.

See <a href="http://w3c.github.io/webvtt/#example-0c2976c9">http://w3c.github.io/webvtt/#example-0c2976c9</a> for an example.

00:00:00.000 --&gt; 00:00:04.000 position:10%,line-left align:left size:35%
Where did he go?

Without position-align you need to set position to some value that doesn't correspond to what the author actually intends:

00:00:00.000 --&gt; 00:00:04.000 position:27.5% align:left size:35%
Where did he go?

27.5% here is: intended position (10%) + size/2 (35%/2). Not intuitive.

Having this also makes the mapping from other subtitle formats to WebVTT (and back) more straightforward.</pre>
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