ISSUE-438: Forbidden #length-cell

#length-cell in TVTT

Forbidden #length-cell

TTML WebVTT mapping note
Raised by:
Pierre-Anthony Lemieux
Opened on:
#length-cell is forbidden, but can't "c" coordinates be readily be converted to percentage coordinates by merely dividing the horizontal (vertical) component by the number of cells in the horizontal (vertical) direction?

I mention this because, in the process of drafting IMSC1, there was a strong request to support "c" coordinates.
Related Actions Items:
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Related emails:
  1. {agenda} TTWG Meeting 2015-10-22 (from on 2015-10-21)
  2. {agenda} TTWG Meeting 2015-09-24 (from on 2015-09-23)
  3. ISSUE-438: Forbidden #length-cell [TTML WebVTT mapping note] (from on 2015-09-23)

Related notes:

Cells are not recommended to be used in the TVTT profile because they have no no counterpart in VTT. Cells can be easily converted into percentages but this should be done in the pre-processing step so that the length metric values are already aligned with WebVTT in the TVTT document.

In IMSC 1 the cell metric is generally not allowed apart from the use in the #ebutts:linePadding extension. The strong request in the IMSC 1 drafting was not to allow the length metric feature "cell" but the feature #cellResolution. This is needed to have the proper base to calculate the initial value of fontSize.

Andreas Tai, 18 Oct 2015, 10:31:44

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