Inpute re: TTML2

Good morning/evening,

Below are potential topics of discussion in light of my initial review
of the most recent TTML2 ED.

A number of comments concern divergence between TTML2 ED, and SMPTE ST
428-7 and SMPTE-TT. It is entirely possible that the SMPTE
specifications are in error. IMHO the world does not however need
further divergence between timed text formats, so, at minimum, I
recommend that TTWG communicate its decisions to SMPTE.

Best,

-- Pierre

> Forced Display

- the specification would benefit from a definition and example (see IMSC1)
- how can a profile support Forced Display without having to implement
the full conditional language?

> image positioning

smpte:backgroundImageHorizontal and smpte:backgroundImageVertical
allow positioning of "the background image of a rendered area",
including using percentages. Does TTML2 allow positioning of <image>
within a region, other than using tts:displayAlign?
tts:backgroundPosition applies only to non-content images.

> ttp:mediaOffset

The relationship between ttp:mediaOffset, root temporal extent,
implicit duration of the body element, computed duration of the body
element, body@start would benefit from a diagram.

> """The ttp:mediaOffset attribute is used to specify the temporal offset between the begin time of the root temporal
> extent and the begin time of a related media object when operating in a Media Time Base or a SMPTE Time Base."""

A container typically controls the synchronization between audio,
video and subtitles. Why not simply move the relative start time of
the subtitle essence within the container instead of changing the
subtitle essence itself?

> [root temporal extent] The temporal extent (interval) defined by the temporal beginning and ending of a
> document instance in relationship with some external application or presentation context.

Why is the root temporal extent defined in relationship with some
external application or presentation context? Isn't it intrinsically
defined by the smallest and largest computed time value within the
document?

> In particular, the statement must identify the utilized or supported TTML vocabulary profile(s) as defined by 5.2 Profiles,

Section 5.2 does not define "TTML vocabulary profile".

> """if the ttp:contentProfiles attribute is specified using the all(...) function syntax or using no function syntax, i.e., as only a list of
> designators, then the effective content profile is the combined profile specification set produced by combining the combined profile
> specification sets of the designated profiles, where the mostRestrictive content profile combination method applies;"""

What would be an example of the use of all(...) function syntax?

> The tts:textEmphasis attribute is used to specify a style property that determines whether and how text emphasis marks are presented on affected content.

What are "text emphasis marks"? A reference would be useful.

> 10.2.3 tts:backgroundImage

This seems to have a much narrower scope than smpte:backgroundImage.
It would be good to rename to prevent confusion, or add a prominent
warning.

> tts:position

what is the use case for tts:position?

> tts:textCombine

As far as I can tell this is substantially different than the HGroup
feature in ST 428-7. Specifically, the horizontal text in ST 428-7 is
not "combin[ed] into an em square of the surrounding vertical text,"
but rather set horizontally with a font size selected by the author.

> tts:textOrientation

sidewaysRight/sidewaysLeft specify rotation of glyphs from horizontal
scripts in vertical writing modes. The Rotate feature in ST 428-7 does
not contain this limitation, but merely notes that "this is most
commonly used to present special characters in a text string that is
being displayed vertically."

> tts:ipd

tts:ipd does not allow negative spacing, as allowed by the Space
feature in SMPTE ST 428-7.

Received on Thursday, 29 January 2015 06:38:30 UTC