Disposition of comments for the Timed Text Working Group

------------------------------
4.1 General
------------------------------
From IMSC 1:
"In addition, the Text Profile subtitle document SHOULD be associated
with the Image Profile subtitle document such that, when image content
is encountered, assistive technologies have access to its corresponding
text form."

As far as I could see there is no defined method to link a Text profile
document to an Image Profile document through an element in the document
themselves. So it may helpful to add that his has to be done through an
external setting.

It would be good to give more emphasis that a presentation processor
should not reject a document "with foreign namespace elements or
attributes".

Examples for possible edits:
a) "...*The subtitle document SHALL be processed but* such elements and
attributes may be ignored by the presentation processor or
transformation processor."

b) "A *conforming* subtitle document may contain elements and attributes
that are neither specifically permitted nor forbidden by a profile."

It may be a good idea to align this paragraph with the section in TTML
5.3.2. As far as I can see it is not explicitly forbidden to use the
IMSC namespaces for extensions. So either in IMSC 1 5.3 or somewhere
else an additional constraint may be added.

-----------------------------------
5.10 Features (Common features) #length-cell feature
-----------------------------------
IMSC 1 states that the #length-cell feature shall not be used. The
line-padding extension uses the cell metric. Not sure if this causes a
problem. On the one hand the extensions are "outside" of TTML 1 on the
other hand they use the cell metric as defined by TTML 1.

-----------------------------------
5.10 Features (Common features) -#length feature
-----------------------------------
The #length feature includes the support of the "c" metric
(http://www.w3.org/TR/ttml1/#feature-length). So you may add a
restriction here.

------------------------------
3. Conformance
------------------------------
The term "subtitle document" is not defined in IMSC 1 and TTML 1 but
used frequently in a normative context. It may be helpful to define it
in Section 2.

------------------------------
5.7.3 itts:forcedDisplay - value matrix
------------------------------
In general I would welcome a bit more text about the details of value
combinations. There is text for "displayForcedMode=true,
itts:forcedDisplay=false" but not for "displayForcedMode=true,
itts:forcedDisplay=true". Maybe a matrix would be helpful with
tts:visibilily (visible, hidden), displayForcedDisplay parameter (true,
fase) annd itts:forcedDisplay (true, false).

------------------------------
5.7.3 itts:forcedDisplay - Informative Note
------------------------------
The first note could possibly be improved if it is noted that this has
an effect only if a "non-transparent background" is directly defined for
the region (e.g. in most cases I have seen for the usage of EBU-TT-D the
background will be applied through the content elements).

------------------------------
5.7.4 ittm:altText - Optionality of attributes
------------------------------
For the XML Representation you may repeat the part from 2.3 TTML 1 where
it states that bold-face attribute names are required and the others are
optional (personally I would prefer the keyword "REQUIRED" after the
attribute name). Without that it may not be clear if the attributes are
optional or required.


------------------------------
5.7.4 ittm:altText - Typo
------------------------------
End of "Note:": Replace ". ." with "."

------------------------------
5.10 Features (Common)
------------------------------
#timing: It may be helpful to describe what you mean with the same
syntax (e.g. is 00:00:01, 00:00:01.0 and 00:00:01.000 a different syntax?)

------------------------------
6.3 Features (Text Profile)
------------------------------
#textAlgin: A reference to the definition of the "defaultRegion" in TTML
1 would be helpful. I assume that ony the TTML experts know what the
defaultRegion is (e.g. some implementers gave in a TTML document
"defaultRegion" as value for xml:id).

-----------------------------
8.2 Reference Fonts
-----------------------------
A reference to presentation processors and transformation processors may
be helpful. A presentation processor SHALL lay out the text according to
the metrics and a transformation processor should use this metrics for
any calculation.

Dear all,

As the public review period nears its end, I'd like to highlight a positive addition to the imsc spec to facilitate image based subtitling.

A basic image based subtitling script file will normally contain:
Incue/Outcue
Image name/url
Image position
Optionally, image size may be specified, and the overall size of the canvas may be specified.


Imsc by inclusion of backgroundimage just about allows for these. But the specification of image size and position is very convoluted.

For image based subtitling, position and size of the image in relation to the video is paramount.


It would be really good if tts:origin and tts:extent were enabled on div for image based subtitling; at the moment I cannot see how they are allowed. Please correct me and include a sample in the document if I am wrong.
It would also be good to be explicit about image scaling. Ideally, the image should be scaled to match the specified image extent (with some notes that if this scaling is close to 1:1 after taking into account player size, etc., then the decoder may prefer not to scale to retain quality).


This modification would make image based subtitling in imsc a relatively simple and easy to understand construct. It makes it almost as simple to write as current extant image + script formats, and (I would imagine) make it relative easy to parse.



Modified example from http://en.wikipedia.org/wiki/User:Cwmwenallt/SMPTE-TT (i'm not claiming this was correct to start with!).


<tt xmlns:smpte="http://www.smpte-ra.org/schemas/2052-1/2010/smpte-tt"
xmlns="http://www.w3.org/ns/ttml"
xmlns:ttm="http://www.w3.org/ns/ttml#metadata"
xmlns:tts='http://www.w3.org/ns/ttml#styling'
xml:lang="en">
<head>
<layout>
<region xml:id="imageRegion" tts:color="transparent" tts:origin="0% 0%" tts:extent="100% 100%" >
<set begin="0.19305s" end="0.21581s" tts:origin="0px 2px" tts:extent="4px 8px" />
<set begin="5.89876s" end="8.09467s" tts:origin="230px 50px" tts:extent="243px 58px" />
<set begin="8.20106s" end="10.1922s" tts:origin="202px 50px" tts:extent="302px 64px" />
<set begin="10.3032s" end="12.2943s" tts:origin="180px 402px" tts:extent="341px 32px" />
</region>
</layout>
</head>
<body>
<div region="imageRegion">
<div begin="0.19305s" end="0.21581s" smpte:backgroundImage="Subtitles_EN/SPU0.png">
<p>[Example SMPTE-TT file]</p>
</div>
<div begin="5.89876s" end="8.09467s" smpte:backgroundImage="Subtitles_EN/SPU1.png">
<p>Hello Wikipedia</p>
</div>
<div begin="8.20106s" end="10.1922s" smpte:backgroundImage="Subtitles_EN/SPU2.png">
<p>This is a basic Example</p>
</div>
<div begin="10.3032s" end="12.2943s" smpte:backgroundImage="Subtitles_EN/SPU3.png" >
<p>of pop on style captioning with preformatted background images</p>
</div>
</div>
</body>
</tt>


Becomes (I did not add the required namespace):

<tt xmlns:smpte="http://www.smpte-ra.org/schemas/2052-1/2010/smpte-tt"
xmlns="http://www.w3.org/ns/ttml"
xmlns:ttm="http://www.w3.org/ns/ttml#metadata"
xmlns:tts='http://www.w3.org/ns/ttml#styling'
xml:lang="en">
<head>
<layout>
<region xml:id="imageRegion" tts:color="transparent" tts:origin="0% 0%" tts:extent="100% 100%" >
</region>
</layout>
</head>
<body>
<div region="imageRegion">
<div begin="0.19305s" end="0.21581s" smpte:backgroundImage="Subtitles_EN/SPU0.png" tts:origin="0px 2px" tts:extent="4px 8px" >
<ittm:altText>[Example SMPTE-TT file]</ittm:altText>
</div>
<div begin="5.89876s" end="8.09467s" smpte:backgroundImage="Subtitles_EN/SPU1.png" tts:origin="230px 50px" tts:extent="243px 58px" >
<ittm:altText>Hello Wikipedia</ittm:altText>
</div>
<div begin="8.20106s" end="10.1922s" smpte:backgroundImage="Subtitles_EN/SPU2.png" tts:origin="202px 50px" tts:extent="302px 64px" >
<ittm:altText>This is a basic Example</ittm:altText>
</div>
<div begin="10.3032s" end="12.2943s" smpte:backgroundImage="Subtitles_EN/SPU3.png" tts:origin="180px 402px" tts:extent="341px 32px" >
<ittm:altText>of pop on style captioning with preformatted background images</ittm:altText>
</div>
</div>
</body>
</tt>



Best regards,

Simon Hailes.
p.s. please reply direct if you have any comments/questions. I don't monitor the mailing lists....

Simon Hailes | Chief Technology Officer | Screen
Main Line : +44 1473 831700 | Ext : 2161 |Mobile : +44 7802 759311 | Fax : +44 1473 830078
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Editorial:

8.1.4
NRGA(Ii)= (width of Ii ) ? height of Ii )
- there appears to be an excess right parethensis

generally
An example document, or several, would be a very helpful addition.

--
Charles McCathie Nevile - web standards - CTO Office, Yandex
chaals@yandex-team.ru - - - Find more at http://yandex.com

------------------------
Annex B Forced Content
------------------------
A code example may be an illustrative help for the shown use case.

Editorial:

3. Conformance

The document defines clearly that it uses the terms MUST, SHOULD, MAY and so on in line with RFC2119. This is good practice, and helps many spec users recognise what is meant. But it uses (beginning about the next line) SHALL throughout, which is undefined, and an uncommon word in modern english. I suggest replacing every instance of shall with must.

Editorial:

5.7
The definitions of each item here would be far clearer with an actual example.
It would be very helpful to choose a single formalism for syntax.

The example of an attribute which *I think* can be either

ittp:progressivelyDecodable="true"
or
ittp:progressivelyDecodable="false"
would be more helpful if it were described much as the following attribute, which says what elements it applies to, what values it can take, etc.

Hi Pierre,

While reading the draft I noticed that the SMPTE spec does not have a
direct link to the document, which is not really convenient for readers.
Could you add it?

Cyril

Dear Sir or Madam,

As a follow-up to my earlier email, the DVB TM-SUB group (which I chair)
met this morning to collate comments on your latest working draft of IMSC1.

The IMSC1 specification has been reviewed by some of the DVB members.
The common view
was that IMSC1 is a candidate technology for our next subtitle
specification and it provides
a compatible update from EBU-TT-D which is specified in DVB's profile of
MPEG DASH.

Therefore the TM-SUB group requests that W3C endeavour to maintain IMSC1
as a super-set of EBU-TT-D.

The group noted the following restrictions that needed to be applied to
EBU-TT-D to achieve IMSC1 compatibility: UTF8 encoding and a maximum of
4 simultaneous regions.

Peter Cherriman (DVB TM-SUB chairman)