--- a/608toVTT/608toVTT.html Thu Nov 08 19:24:40 2012 +1100
+++ b/608toVTT/608toVTT.html Thu Nov 08 22:43:34 2012 +1100
@@ -91,7 +91,7 @@
<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>
+ <p>Note that CEA-608 has been defined for US television and therefore only horizontal ltr rendered text is created in WebVTT cues. CEA-708 has some support for vertically rendered and rtl text through caption text settings.</p>
</section>
@@ -106,7 +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 <a href="http://www.w3.org/community/texttracks/wiki/MultiCueBox">WebVTT "Regions""</a>. 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>
@@ -415,7 +415,7 @@
</p>
<p>
- Within the Caption Screen, CEA-708 defines "Caption Windows" through which the caption text is rendered. For WebVTT we map CEA-708 "Caption Windows" to <a href="http://www.w3.org/community/texttracks/wiki/MultiCueBox">WebVTT Regions</a>. It is also possible to use plain WebVTT cues, but those have limited functionality, e.g. don't allow you to style the Region (e.g. Window background colors), or position with anchor points and anchor location, or do roll-up.
+ Within the Caption Screen, CEA-708 defines "Caption Windows" through which the caption text is rendered. For WebVTT we map CEA-708 "Caption Windows" to <a href="http://www.w3.org/community/texttracks/wiki/MultiCueBox">WebVTT Regions</a>. It is also possible to use plain WebVTT cues, but those have limited functionality, e.g. don't allow styling of the Region (e.g. Window background colors or fade in), or position with anchor points and anchor location, or do roll-up, so will not result in a perfect representation of CEA-708 captions. We will not regard this option further here.
</p>
<p>
@@ -617,23 +617,132 @@
</section>
<section>
+ <h2>Caption Text Settings in CEA-708</h2>
+ <p>
+ CEA-708 defines several settings of caption text within a Caption Window. This section explains how to convert them to WebVTT cue settings.
+ </p>
+
+ <h3>Justification and alignment</h3>
+ <p>
+ CEA-708 defines several different text justification settings for text within a Caption Window. These settings are translated into WebVTT cue settings, since there is no justification attributes on WebVTT Regions. The relevant cue setting is called "align":
+ </p>
+
+ <table border="1">
+ <thead>
+ <tr>
+ <td>CEA-708 Caption Window Justification</td>
+ <td>WebVTT Cue align setting</td>
+ </tr>
+ </thead>
+ <tbody>
+ <tr>
+ <td>left</td>
+ <td>align:start</td>
+ </tr>
+ <tr>
+ <td>right</td>
+ <td>align:end</td>
+ </tr>
+ <tr>
+ <td>center</td>
+ <td>align:middle</td>
+ </tr>
+ <tr>
+ <td>full</td>
+ <td>no equivalent in WebVTT - use "middle" instead.</td>
+ </tr>
+ </tbody>
+ </table>
+
+ <p>
+ Note that WebVTT does not have an equivalent for fully justified text. It would be possible to add such a value or to use the CSS text-align:justify directive, but neither is currently supported in WebVTT. Since fully justifying text is not usually recommended for good quality subtitles or captions, there should be no need for this.
+ </p>
+
+
+ <h3>Text direction</h3>
+ <p>
+ CEA-708 defines several different text rendering directions within a Caption Window. These settings are translated into WebVTT cue settings, since there is no direction attributes on WebVTT Regions. The default cue text rendering direction is "horizontal". The relevant cue setting to introduce vertical text is called "vertical". The following explains how the mapping is achieved:
+ </p>
+
+ <table border="1">
+ <thead>
+ <tr>
+ <td>CEA-708 Caption Window Print Direction</td>
+ <td>WebVTT Cue text and settings</td>
+ </tr>
+ </thead>
+ <tbody>
+ <tr>
+ <td>left-to-right</td>
+ <td>horizontal is the default; no special cue setting</td>
+ </tr>
+ <tr>
+ <td>right-to-left</td>
+ <td>horizontal is the default; use UTF-8 characters to change to rtl text</td>
+ </tr>
+ <tr>
+ <td>top-to-bottom</td>
+ <td>vertical:rl or vertical:lr, depending on scroll direction</td>
+ </tr>
+ <tr>
+ <td>bottom-to-top</td>
+ <td>vertical:rl or vertical:lr; use UTF-8 characters to change directionality</td>
+ </tr>
+ </tbody>
+ </table>
+
+
+ <h3>Scroll direction</h3>
+ <p>
+ CEA-708 defines several different scroll directions within a Caption Window. These settings are translated into the WebVTT Region attribute "scroll":
+ </p>
+
+ <table border="1">
+ <thead>
+ <tr>
+ <td>CEA-708 Caption Window Scroll Direction</td>
+ <td>WebVTT Region attribute</td>
+ </tr>
+ </thead>
+ <tbody>
+ <tr>
+ <td>top-to-bottom for horizontal text</td>
+ <td>scroll:down</td>
+ </tr>
+ <tr>
+ <td>bottom-to-top for horizontal text</td>
+ <td>scroll:up</td>
+ </tr>
+ <tr>
+ <td>left-to-right for vertical text</td>
+ <td>if vertical:lr, then scroll:down; else scroll:up</td>
+ </tr>
+ <tr>
+ <td>right-to-left</td>
+ <td>if vertical:rl, then scroll:down; else scroll:up</td>
+ </tr>
+ </tbody>
+ </table>
+
+
+ <h3></h3>
+ <p>
+ </p>
+ </section>
+
+ <section>
<h2>Pop-on Captions</h2>
<p>
CEA-608 has a maximum of 4 rows of captions, which can be placed anywhere in the safe caption area.
</p>
<p>
- In WebVTT, pop-on captions are mapped to cues. Cues without explicit positioning are simply mapped to WebVTT cues
-
-
- The translation software will ascertain the following properties:
+ In WebVTT, pop-on captions are mapped to cues. Their start time and end time are determined by the time that the CEA-608 memory is flipped such that the caption text becomes visible/removed. The caption text of the CEA-608 pop-on caption is placed in the cue content. Cue settings such as line and position settings are set as described in the section on "Positioning in CEA-608".
</p>
- <ul>
- <li>No cues in the WebVTT file with their intervals defined by start and end time overlap with other cues’ intervals unless they are positioned in different locations on-screen.</li>
- <li>No more than 4 rows of text are present in a cue.</li>
- <li>If a specific location is given for the caption, add this location to the cue setting.</li>
- <li>If the rows of text of one CEA-608 caption are to be rendered into vastly different positions on screen, subdivide the rows into separate cues that are active for the exact same interval, but have different locations in their cue settings.</li>
- </ul>
+
+ <p>
+ If the rows of text of one CEA-608 caption are to be rendered into vastly different positions on screen, you should subdivide the rows into separate cues that are active for the exact same interval, but have different locations in their cue settings.
+ </p>
<p>
Example of a typical WebVTT file with pop-on captions:
@@ -660,6 +769,9 @@
00:00:06.277 --> 00:00:07.299
I'm the kind that pays better.
</pre>
+
+ <p>
+ CEA-708 pop-on captions rely on a Caption Window to be defined and mapped to a WebVTT Region as described in the section on "Positioning in CEA-708". Further attributes both of the Region and the individual cue are described in section "Caption Text Settings in CEA-708".
</section>
<section>