--- a/608toVTT/608toVTT.html Thu Nov 08 13:14:58 2012 +1100
+++ b/608toVTT/608toVTT.html Thu Nov 08 16:58:08 2012 +1100
@@ -90,6 +90,8 @@
<p>This document does not target user agent developers. User agents (UAs) are expected to implement the [[WEBVTT]] specification. Any conversion tool that follows the suggestions in this document and delivers WebVTT files as converted by the suggestions in this document together with an appropriate HTML page and a style sheet as explained in <a href="#browsers" class="sectionRef"></a> can expect UAs to render their WebVTT file on their videos correctly.</p>
<p>The aim of this document is to help developers of tools that convert between different caption formats to implement best practice for creating WebVTT files that support CEA-608 or CEA-708 features.</p>
+
+ <p>Note that CEA-608 and CEA-708 have been defined for US television and therefore only horizontal ltr rendered text is created in WebVTT cues.</p>
</section>
@@ -104,7 +106,7 @@
</p>
<p>
- A WebVTT file consists at its core of a series of so-called cues, which contain a start time, an end time, cue settings, and the cue text, which is rendered in browsers for WebVTT files of kind "subtitles" or "captions". Styling of character attributes is provided through markup of the text in a similar fashion to how HTML marks up text. Cues are either rendered directly to the video viewport, or into a so-called "Region". Regions are similar to CEA-708 windows.
+ A WebVTT file consists at its core of a series of so-called cues, which contain a start time, an end time, cue settings, and the cue text, which is rendered in browsers for WebVTT files of kind "subtitles" or "captions". Styling of character attributes is provided through markup of the text in a similar fashion to how HTML marks up text. Cues are either rendered directly to the video viewport, or into a so-called <a href="http://www.w3.org/community/texttracks/wiki/MultiCueBox">WebVTT "Regions""</a>. Regions are similar to CEA-708 windows.
</p>
<p>
@@ -206,7 +208,7 @@
</p>
<p>
- In WebVTT CEA-608, the safe caption area is set by the video player by setting "edge margin" to 10%.
+ If the safe caption area is to be preserved when using WebVTT, the video player can set the "edge margin" variable to 10% in the WebVTT rendering instructions. The edge margin only affects WebVTT cues that are not provided with explicit, percentage-based line positioning. So it mostly only affects cues that are rendered in their default position.
</p>
<p>
@@ -227,7 +229,7 @@
<li>CEA-608 indent positions are every 10% of the video width, because CEA-68 defines a new indent position every 4 columns/characters.</li>
</ul>
<p>
- When translating to WebVTT only the final position of the caption text shall be translated.
+ When translating to WebVTT only the final position of the caption text shall be translated. CEA-608 captions are generally translated to WebVTT cues with their position specified in cue settings. Only CEA-608 captions that are roll-up captions are rendered into WebVTT "Regions".
</p>
<p>
@@ -240,7 +242,7 @@
</p>
<p>
- The PAC row number maps to a line cue setting in WebVTT CEA-608. Since WebVTT defines its line numbering scheme based on the height of the font in use, WebVTT CEA-608 makes use of the percentage line cue setting of WebVTT:
+ The PAC row number maps to a line cue setting in WebVTT CEA-608. For rollup captions the calculation is the same, but the resulting number is applied to the Region rather than the cue directly, as described in the "Rollup Captions" section. Since WebVTT defines its line numbering scheme based on the height of the font in use, WebVTT CEA-608 makes use of the percentage line setting of WebVTT:
</p>
<pre>
line:x%
@@ -328,7 +330,7 @@
</pre>
<p>
- Use the following percentage values to represent CEA-608 indent positions:
+ For rollup captions the calculation is the same, but the resulting number is applied to the Region rather than the cue directly, as described in the "Rollup Captions" section.Use the following percentage values to represent CEA-608 indent positions:
</p>
<table border="1">
@@ -395,6 +397,15 @@
<p>
For example, for an existing cue position setting of 20% (column 5), a Tab Offset of 3 will create a cue position setting of 27.5%.
</p>
+
+ <p>
+ For rollup captions the position setting is set on the cue, too, but since the cue is already positioned by the Region that it belongs it, its position is simply calculated from the tab offset:
+ </p>
+ <pre>
+t=tabOffset*2.5
+position:t%
+ </pre>
+
</section>
<section>
@@ -414,6 +425,7 @@
Region: id=window1 width=100% height=4 regionanchor=50%,100% viewportanchor=50%,50% scroll=up
</pre>
+
<h3>Caption Window Priority</h3>
<p>
@@ -463,6 +475,10 @@
</tbody>
</table>
+ <p>
+ Note that if two Regions end up being active at the same time (i.e. having cues at the same time) and being in the same "layer" and overlapping on the viewport, the one defined last overlaps the one defined earlier.
+ </p>
+
<h3>Caption Window Anchor Points</h3>
<p>