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[webvtt] definition of a title safe area for overscan

From: guohuideng via GitHub <sysbot+gh@w3.org>
Date: Tue, 01 May 2018 00:57:54 +0000
To: public-texttracks@w3.org
Message-ID: <issues.opened-319084463-1525136273-sysbot+gh@w3.org>
guohuideng has just created a new issue for https://github.com/w3c/webvtt:

== definition of a title safe area for overscan ==
1. What is the problem
a general description of overscan and title safe concept is here
https://en.wikipedia.org/wiki/Overscan

In short, the video/graphic rendering area is not guaranteed on some display devices, So the very outer portion of intended video/graph image may be  "cut off" by the boundary of the display device. This problem was more pronounced in older TV but they still exist even on modern devices.

Therefore the content provider usually need to prepare their video/graphics for potential overscan problem, by putting the most important content away from the boundary of the video/graphics, so even if the outer potion is cut off the video/graphics won't break.

Text is special because it cannot only be cut off, but also should not be distorted. So the suggested "safe area" is even smaller.

2. Who is having the problem
A renderer that uses TV as display device(like Chromecast) would risk from overscan problem if put the text too close to the boundary of the image, it is better to take a precautionary measure: make sure that the text is rendered within the title safe area.  

There is no strict definition of "how big the title safe area should be". There are only commonly accepted practice, like 5% margin on each side.

3. The problem for web
Renderers that doesn't use TV( in full screen mode) is unlikely to suffer from overscan problem.   

Meanwhile, some other thoughts of mine: 1.)I don't think forcing a very small margin would hurt any aesthetic result. (in fact I think it looks much better than having the text touching the boundary.) 2) Also, a vast majority of the content I know of already have a much bigger margin than that is required by the "title safe" concept. So enforcing such "minimal margin" would only affect on a small portion of the content.
  

Please view or discuss this issue at https://github.com/w3c/webvtt/issues/442 using your GitHub account
Received on Tuesday, 1 May 2018 00:58:21 UTC

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