Added a metadata header field for AspectRatio for CEA-708, so we can distinguish between 4:3 and 16:9.
authorSilvia Pfeiffer
Tue, 22 Jan 2013 18:47:55 +1100
changeset 51 f11322440708
parent 50 514975d592d5
child 52 580a3e4c4f7f
Added a metadata header field for AspectRatio for CEA-708, so we can distinguish between 4:3 and 16:9.

Closes https://www.w3.org/Bugs/Public/show_bug.cgi?id=20566
608toVTT/608toVTT.html
--- a/608toVTT/608toVTT.html	Tue Jan 22 18:03:36 2013 +1100
+++ b/608toVTT/608toVTT.html	Tue Jan 22 18:47:55 2013 +1100
@@ -149,6 +149,20 @@
         </p>
 
         <p>
+          For CEA-708 it is further recommended to add a "AspectRatio" field, which indicates whether a display area of 4:3 or 16:9 is the basis for the calculations. An example CEA-708 WebVTT file header may be:
+        </p>
+        <pre>
+WEBVTT
+Style:
[email protected](cea608.css)
[email protected](cea708.css)
+##
+Kind: captions
+Language: en-US
+AspectRatio: 16:9
+        </pre>
+        
+        <p>
           The @import command on the "Style" field imports the CSS directives defined in the "Rendering in Browsers" section into the WebVTT file. Browsers will use these CSS directives to make use of their rendering engines for styling cues and cue sections of text.
         </p>
 
@@ -489,7 +503,7 @@
         </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.
+          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 is on top of the one defined earlier.
         </p>
 
 
@@ -575,7 +589,7 @@
         </p>
 
         <p>
-          The width of a Caption Window is converted to a WebVTT Region width by multiplying by 2.5, resulting in a percentage Region width setting:
+          The width of a Caption Window is converted to a WebVTT Region width by multiplying by 2.5 if a <b>display area of 4:3</b> is used, resulting in a percentage Region width setting:
         </p>
         <pre>
 w=columns*2.5
@@ -583,6 +597,13 @@
         </pre>
 
         <p>
+          If a <b>display area of 16:9</b> is used, the column width is defined as 1.9% of the video width, because 16x9 requires 42 columns of characters to be rendered on 80% of the video rendering area’s width.</li>
+        <pre>
+w=columns*1.9
+width:w%
+        </pre>
+
+        <p>
           The height of a Caption Window is converted to a WebVTT Region height by multiplying by 5.33, resulting in a percentage Region height setting:
         </p>
         <pre>
@@ -1617,6 +1638,7 @@
         <li>Loretta Guarino Reed, Google</li>
         <li>David Singer, Apple</li>
         <li>Christian Vogler,  Gallaudet University</li>
+        <li>David Ronca, Netflix</li>
       </ul>
   </body>
 </html>