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FW: [imsc] image based subtitle positioning ( LC-2968)

From: Simon Hailes <Simon.Hailes@screensystems.tv>
Date: Fri, 21 Nov 2014 11:51:18 +0000
To: "public-tt@w3.org" <public-tt@w3.org>
Message-ID: <5388058990DE50438A008F31269C7983016B5B9338@SS-IP-EXMB-01.screensystems.tv>
Dear working group,

With respect to the response to my note on image positioning in IMSC:

" Working Group Resolution (LC-2968):
An objective of IMSC 1 is to leverage as much as possible existing TTML 1 implementations, and IMSC 1 is as such based on TTML 1. Allowing tts:extent and tts:origin to have a meaning on elements other than <region> would be a significant departure from this objective. Moreover it is straightforward to create as many <region>s as there are unique combinations of origin and extent across subtitles/captions.

The intent is to include such a feature in TTML 2 (see issue 176)

We have added an informative note at Section 8.3 of https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml-ww-profiles/ttml-ww-profiles.html

describing the use of multiple <region> elements to achieve positioning of individual subtitle/caption."


I understand and agree with the philosophy behind the objective.
Roll on TTML 2, because the splitting of position and image is ugly and ensures that the file cannot be progressively downloadable.


I think it may be useful to extend the note to clarify image use, since the use of images produces several implied (in my mind) constraints not explicitly highlighted:
The wording "the width and height of the region extent associated with the div element shall be specified and shall be equal to the width and height of the image source referenced by the smpte:backgroundImage;" to me implies an EXACT match of width and height.  To me, this further implies that these must be pixel based (otherwise how could they be exact), which in turn requires that the tt element have a tts:extent.
I think the note should mention that as the tts:extent will be a particular value, but the file will likely be used against multiple bitrates/sizes of video, this implies correct and quality scaling of the images such that they appear the same regardless of video resolution.  The implication from CFF-TT of the tts:extent matching other external metadata or matching the video size must be explicitly NOT be carried into this document, as could be construed as forcing production of multiple TTML and images, one for every video size (and it's the lack of simple clarity on this point which leads me to suggest simple clarification in IMSC).


Possible suggested wording:
NOTE
In [ttaf1-dfxp], tts:extent and tts:origin do not apply to div elements. In order to individually position multiple div elements, each div can be associated with a distinct region with the desired tts:extent and tts:origin.
As the tts:extent for the region referenced by the div SHALL be equal to the image size, the implication is that the tts:extent will be in pixels.  Using pixels requires a tts:extent in pixels [6.10 Features] on the tt element, meaning in turn that the overall canvas fills the video area (regardless of actual video pixel dimensions) [6.7.1 ittp:aspectRatio].  A real world player will need to scale images appropriately so they appear at the tts:origin and sized to the tts:extent (i.e. the same relative size and position compared to the video area, regardless of the actual video pixel dimensions).




Best regards,

Simon




Simon Hailes | Chief Technology Officer | Screen
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P Before printing, think about the environment-----Original Message-----
From: tmichel@w3.org [mailto:tmichel@w3.org]
Sent: 13 November 2014 17:54
To: Simon Hailes
Cc: public-tt@w3.org?subject=%5Bimsc%5D
Subject: Re: [imsc] image based subtitle positioning ( LC-2968)

 Dear Simon Hailes ,

The Timed Text Working Group has reviewed the comments you sent [1] on the Last Call Working Draft [2] of the IMSC 1.0 published on 30 Sep 2014. Thank you for having taken the time to review the document and to send us comments!

The Working Group's response to your comment is included below, and has been implemented in the new version of the document available at:
https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml-ww-profiles/ttml-ww-profiles.html.


Please review it carefully and let us know by email at public-tt@w3.org?subject=%5Bimsc%5D if you agree with it or not before 20 November 2014. In case of disagreement, you are requested to provide a specific solution for or a path to a consensus with the Working Group. If such a consensus cannot be achieved, you will be given the opportunity to raise a formal objection which will then be reviewed by the Director during the transition of this document to the next stage in the W3C Recommendation Track.

Thanks,

For the Timed Text Working Group,
Thierry Michel
Philippe Le H├ęgaret
W3C Staff Contacts

 1.
http://www.w3.org/mid/5388058990DE50438A008F31269C7983016B5AE237@SS-IP-EXMB-01.screensystems.tv

 2. http://www.w3.org/TR/2014/WD-ttml-imsc1-20140930/



=====

Your comment on Image Profile:
> 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
> Simon.Hailes@screensystems.tv<mailto:Simon.Hailes@screensystems.tv> |
> www.screensystems.tv<http://www.screensystems.tv> |
> https://twitter.com/screensystems

>
> Visit us at
> SMPTE Annual Technical Conference, Loews Hollywood Hotel, Stand 107,
> October 21-23 Languages & the Media, Hotel Radission Blu, Berlin,
> November 5-7
>
> P Before printing, think about the environment
>
>
> This message may contain confidential and/or privileged information.
> If you are not the intended recipient you must not use, copy, disclose
> or take any action based on this message or any information herein. If
> you have received this message in error, please advise the sender
> immediately by reply e-mail and delete this message. Thank you for
> your cooperation. Screen Subtitling Systems Ltd. Registered in England No.
> 2596832. Registered Office: The Old Rectory, Claydon Church Lane,
> Claydon, Ipswich, Suffolk, IP6 0EQ


Working Group Resolution (LC-2968):
An objective of IMSC 1 is to leverage as much as possible existing TTML 1 implementations, and IMSC 1 is as such based on TTML 1. Allowing tts:extent and tts:origin to have a meaning on elements other than <region> would be a significant departure from this objective. Moreover it is straightforward to create as many <region>s as there are unique combinations of origin and extent across subtitles/captions.

The intent is to include such a feature in TTML 2 (see issue 176)

We have added an informative note at Section 8.3 of https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml-ww-profiles/ttml-ww-profiles.html

describing the use of multiple <region> elements to achieve positioning of individual subtitle/caption.

----



This message may contain confidential and/or privileged information. If you are not the intended recipient you must not use, copy, disclose or take any action based on this message or any information herein. If you have received this message in error, please advise the sender immediately by reply e-mail and delete this message. Thank you for your cooperation. Screen Subtitling Systems Ltd. Registered in England No. 2596832. Registered Office: The Old Rectory, Claydon Church Lane, Claydon, Ipswich, Suffolk, IP6 0EQ
Received on Friday, 21 November 2014 11:51:49 UTC

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