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w3c / ttml2

Timed Text Markup Language 2 (TTML2)
https://w3c.github.io/ttml2/
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Unspecified mapping of shear percentage to shear angle. #1075

Closed palemieux closed 5 years ago

palemieux commented 5 years ago

10.4.5.3 Shear Calculations does not specify the algorithm for converting the shear percentage value into the shear angle.

FWIW, imscJS currently uses arcsin(<% value>) although it is not clear why.

skynavga commented 5 years ago

The intended algorithm is shear angle = shear percentage * 90deg., i.e., that it be a linear mapping, which is what TTPE implements; arcsin(shear percentage) does not produce the intended mapping. I will post a PR that makes the mapping explicit.