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Re: Wrapper not format

From: Adam Twardoch (List) <list.adam@twardoch.com>
Date: Thu, 04 Mar 2010 03:25:08 +0100
Message-ID: <4B8F1A04.904@twardoch.com>
To: Chris Lilley <chris@w3.org>
CC: Thomas Phinney <tphinney@cal.berkeley.edu>, "Tab Atkins Jr." <jackalmage@gmail.com>, www-font@w3.org
Chris Lilley wrote:
> TP> WOFF is a wrapper format rather than a standalone format. WOFF
> TP> wrappers can be deployed around any SFNT based font format, including
> TP> TTF,  TTF/OpenType, OpenType CFF, TTF/AAT, TTF/Graphite (and perhaps
> TP> .dfont?).
> 
> Yes.

In video applications, this is called a "container format" or "wrapper
format" (though "container format" is more popular, I think):
http://en.wikipedia.org/wiki/Container_format_%28digital%29

For example, AVI, MKV, OGG and MP4 are all container formats that can
hold various metadata and data for various streams.

This is different from the "coding format" which specifies in which way
the multimedia contents of each stream is encoded (e.g. AAC, MP3,
MPEG-2, H.264 etc.).

OpenType-TrueType, OpenType-CFF, AAT-TrueType, AAT-CFF,
Graphite-TrueType, Graphite-CFF are different coding formats for digital
font files that use the "sfnt" structure (which are separate from, say,
Type 1 fonts, which use a completely different structure).

In fact, one can make one more analogy: similar to the audio and video
streams in multimedia files, we can identify two kinds of streams in
sfnt-based digital font formats: the glyph imaging "stream" (with the
coding formats TrueType or CFF) and the layout "stream" (with the coding
formats OpenType, AAT or Graphite).

A font that contains both TrueType and CFF glyph outlines is unlikely,
there can be only one of them -- which makes the glyph imaging "stream"
analogous to the video stream (you rather not have two parallel video
streams in a file). On the other hand, a font that contains a mix of
OpenType, AAT and Graphite layout "streams" is more likely, just like
there are multimedia files that have several parallel audio tracks (say,
for English, German and French-dubbed dialog).

Oh, and glyph bitmaps are kind of like subtitles. A bit :)

Following this analogy, .woff, .eot, .otf, .ttf, .ttc, .dfont, FFIL are
different container formats for sfnt-based digital font files.

Regards,
Adam

-- 

Adam Twardoch
| Language Typography Unicode Fonts OpenType
| twardoch.com | silesian.com | fontlab.net

Reporter: "So what will your trip to Ireland look like?"
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Received on Thursday, 4 March 2010 02:25:48 GMT

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