Timed Divs HTML

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The following is a draft.

It is at best incomplete and at worst completely broken. In any case, it is not an "official" Xiph spec/codec, so use with care.



This page specifies a subclass of HTML documents that is a time-aligned text format for audio-visual content. We call the format "timed divs within HTML" or TDHT. It is intended to be used only in a World Wide Web context i.e. everywhere that Web browser functionality is available. Use cases for the format are subtitles, captions, annotations and other time aligned text as listed at http://wiki.xiph.org/index.php/OggText#Categories_of_Text_Codecs .

TDHT may be similar to W3C TimedText DFXP in many respects, but in comparison to DFXP it does not re-invent HTML, CSS and effects, but rather uses existing HTML, CSS and javascript for these. The purpose of DFXP is to create a web-independent exchange format for timed text, which is why it cannot directly be specified as a subpart of HTML.

TDHT in contrast is HTML with a minimum number of changes. TDHT is parsable by any HTML parser. It works with CSS and javascript. No new functionality has to be defined for TDHT.

File Extension

Files in this format are to be of text/x-tdht mime type.

Files in this format should have a file extension of .tdht .

The TDHT format changes from HTML

TDHT files are time-aligned text. This means there is a time association with blocks of text and there is time-based seeking functionality on those blocks of text.

Here is an example TDHT file for subtitles:

    <title>Desperate Housewives - Season 5, Episode 6</title>
    <div start="00:00:00,070" end="00:00:02,270">
      <p>Previously on...</p>
    <div start="00:00:02,280" end="00:00:04,270">
      <p>We had an agreement to keep things casual.</p>
    <div start="00:00:04,280" end="00:00:06,660">
      <p>Susan made her feelings clear.</p>
    <div start="00:00:06,800" end="00:00:10,100">
      <p>So if I was with another woman, that wouldn't bother you? No, it wouldn't.</p>

Right now, TDHT is based on HTML4.01, but it should also be possible to work on HTML5, which is still in flux.

The following changes to HTML4.01 are made for TDHT:

1. The body element

In HTML4.01, the body element is defined as follows:

<!ELEMENT BODY O O (%block;|SCRIPT)+ +(INS|DEL) -- document body -->
  %attrs;                              -- %coreattrs, %i18n, %events --
  onload          %Script;   #IMPLIED  -- the document has been loaded --
  onunload        %Script;   #IMPLIED  -- the document has been removed --

In TDHT1.0 we restrict it to just contain a sequence of div tags:

<!ELEMENT BODY O O (DIV)+ -- document body -->
  %attrs;                              -- %coreattrs, %i18n, %events --
  onload          %Script;   #IMPLIED  -- the document has been loaded --
  onunload        %Script;   #IMPLIED  -- the document has been removed --

The div tags in turn can contain anything that HTML div tags can contain, thus enabling a very flexible, but time-aligned text model.

2. The div element

In HTML4.01, the div element is defined as follows:

<!ELEMENT DIV - - (%flow;)*            -- generic language/style container -->
  %attrs;                              -- %coreattrs, %i18n, %events --

In TDHT1.0 we extend it with start and end time attributes:

<!ELEMENT DIV - - (%flow;)*            -- generic language/style container -->
  %attrs;                              -- %coreattrs, %i18n, %events --
  start           %Time;    #IMPLIED   -- start time
  end             %Time;    #IMPLIED   -- end time

The Time entity is defined in HTML5: http://www.whatwg.org/specs/web-apps/current-work/#valid-time-string .

Rendering in a Web Browser

A TDHT file is meant to be associated with a audio or video file and rendered in a Web browser in sync with the audio or video file.

For security reasons, the TDHT file is not rendered into an existing HTML page, but rather creates its own iframe-like new nested browsing context.

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