ISSUE-418: semantics of ttp:aspectRatio is ambiguous

semantics of ttp:aspectRatio is ambiguous

State:
CLOSED
Product:
TTML IMSC 1.0
Raised by:
Glenn Adams
Opened on:
2015-09-21
Description:
The semantics of ttp:aspectRatio is ambiguous with respect to the presence of tts:extent on the root element. Which takes priority if both are present?
Related Actions Items:
No related actions
Related emails:
  1. {minutes} TTWG Meeting 2015-10-30 (from nigel.megitt@bbc.co.uk on 2015-10-30)
  2. {minutes} TTWG Meeting 2015-10-22 (from nigel.megitt@bbc.co.uk on 2015-10-22)
  3. {agenda} TTWG Meeting 2015-10-22 (from nigel.megitt@bbc.co.uk on 2015-10-21)
  4. {minutes} TTWG Meeting 2015-10-15 (from nigel.megitt@bbc.co.uk on 2015-10-15)
  5. {agenda} TTWG Meeting 2015-10-15 (from nigel.megitt@bbc.co.uk on 2015-10-14)
  6. IMSC 1 issues (from nigel.megitt@bbc.co.uk on 2015-10-08)
  7. {agenda} TTWG Meeting 2015-10-01 (from nigel.megitt@bbc.co.uk on 2015-10-01)
  8. {agenda} TTWG Meeting 2015-09-24 (from nigel.megitt@bbc.co.uk on 2015-09-23)
  9. Update re: outstanding IMSC1 issues (from pal@sandflow.com on 2015-09-21)
  10. ISSUE-418: semantics of ttp:aspectRatio is ambiguous [TTML IMSC 1.0] (from sysbot+tracker@w3.org on 2015-09-21)

Related notes:

tts:extent on the root element sets the absolute size of the root container in pixels, i.e. it is used to calculate positions express in "px" units relative to the root container. ttp:aspectRatio is then used to map the root container to the related video object.

So, for example, assuming tts:extent="400px 300px" and ittp:aspectRatio="4 3" and a related video object with 4:3 aspect ratio, a tts:origin="40px 30px" would be positioned 10% from the top and left of the root container, and 10% from the top and left of the related video object.

Would an example along these lines help?

Pierre-Anthony Lemieux, 21 Sep 2015, 17:19:12

yes, it would help; but i would suggest showing examples for both a case where the aspect ration of the related video object is the same as the specified aspect ratio, and another example where they do not match

Glenn Adams, 24 Sep 2015, 15:01:15

Addressed at https://dvcs.w3.org/hg/ttml/rev/1dccbd5eb855

Pierre-Anthony Lemieux, 7 Oct 2015, 23:52:52

To address Glenn's point about an example where the aspect ratio does match, I'd suggest changing the Example 2 first line text from:

"Region "A" in the following document would be positioned 20% from the left edge of a Related Video Object with aspect ratio of 16:9."

to:

"Region "A" in the following document would be positioned 20% from the left edge of a Related Video Object whose aspect ratio is 16:9, or 10% from the left edge of a Related Video Object is 4:3."

As an aside, the choice of numbers that results apparently magically in the values coming out to 10% and 20% may be slightly confusing to some readers - I had to do the maths to understand how that came about since it was not obvious why 20% would be the outcome on 16:9. I don't know if there is a better example though. Possibly a diagram would help too?

Nigel Megitt, 8 Oct 2015, 09:50:53

Addressed at https://dvcs.w3.org/hg/ttml/rev/b02cabf02146

Pierre-Anthony Lemieux, 15 Oct 2015, 15:38:28

[nigel]: [Meeting 2015-10-30] Proposed note: Note: The ittp:aspectRatio parameter effectively defines the intended display aspect ratio (DAR) of the root container, while the tts:extent style property on the root element effectively defines the intended storage aspect ratio (SAR) of the root container.

30 Oct 2015, 04:46:45

Further tweaks at https://dvcs.w3.org/hg/ttml/rev/2cd6f1c06e57 per 20151030 meeting

Pierre-Anthony Lemieux, 30 Oct 2015, 04:51:20

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David Singer <singer@apple.com>, Nigel Megitt <nigel.megitt@bbc.co.uk>, Chairs, Thierry Michel <tmichel@w3.org>, Philippe Le H├ęgaret <plh@w3.org>, Atsushi Shimono <atsushi@w3.org>, Staff Contacts
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