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w3c / ttml-webvtt-mapping

TTML to WebVTT mapping
https://w3c.github.io/ttml-webvtt-mapping/
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#length-pixel forbidden #7

Open plehegar opened 8 years ago

plehegar commented 8 years ago

Although specifying lengths in pixels should generally be discouraged, I have seen many TTML documents use them.

As long as tts:extent is specified on <tt> using "px" metric, can't "px" coordinates be converted to percentage coordinates by merely dividing the horizontal (vertical) component by the number of tts:extent pixels in the horizontal (vertical) direction?

(raised by Pierre-Anthony Lemieux on 2015-09-23) From tracker issue http://www.w3.org/AudioVideo/TT/tracker/issues/439

andreastai commented 8 years ago

This is related to the general mapping approach taken in the document to make an "intermediate" document type as close as possible to WebVTT. WebVTT does not support "absolute" positioning with pixel. But you may allow pixel as length metric for font-size (this is supported in CSS).

Andreas Tai, 27 Oct 2015 From tracker issue http://www.w3.org/AudioVideo/TT/tracker/issues/439

palemieux commented 8 years ago

Shouldn't the pre-processing step of converting "px" to "percentage" be included in "Pre-processing: Positioning"?