[mpeg-OTspec] The font top-level registration I-D

Levantovsky, Vladimir Vladimir.Levantovsky at AgfaMonotype.com
Thu Aug 26 21:12:43 CEST 2004

Hi David,

I fully support the concept of top-level MIME registration for fonts. As you
rightly pointed out in the document, fonts provide the glyph data to create
the visual representation of the characters and this information can be
presented in a number of different formats.

I would like to make a few comments:

1. Section 4.1 "OpenType".
"File extensions" - the proposed draft says, " "otf" is the common extension
used;  ttf may be used  for TrueType fonts, but this is not recommended".

While it's true that the "otf" extension can be used for OpenType fonts with
either TrueType or CFF outlines, the "ttf" extension is commonly used for
OpenType fonts with TrueType outlines. The reason for that is compatibility
with other platforms - it allows OpenType .TTF fonts be used on those
platforms that support TrueType rendering only and do not have OpenType
Layout engine. An OpenType font with TrueType outlines will still be usable
and treated as regular, full-features TTF font, although not all
capabilities of OpenType fonts may be utilized on a particular platform.

I suggest modifying the "File extensions" description as saying:
"OTF is the common extension used; TTF may be used for OpenType fonts with
TrueType outlines, TTC is used for TrueType Collections fonts"

2. Section 4.2 "SFNT"
"Interoperability Considerations" - I suggest to mention that SFNT font
files may contain tables that are proprietary and/or application specific.
These table definitions may not be available to a general public, therefore,
it may be impossible to create a compliant implementation. Strictly
speaking, SFNT structure does not define a list of required tables and/or
their content; it is feasible that someone may create a perfectly valid SFNT
file with arbitrary set of tables containing information that may not even
be a font!

"Font extensions"
For the same reasons mentioned above we can only *hope* that the content of
SFNT file is the font. Even if this is the case, an "application-specific"
SFNT font may use arbitrary extensions. For example, what is now known as
"MPEG-4 compressed font format" is using SFNT font structure with the custom
table added and the extensions .a3a for compressed TTF fonts and .a3b for
compressed TTC fonts.

Best regards,

-----Original Message-----
From: Dave Singer [mailto:singer at apple.com] 
Sent: Thursday, August 26, 2004 1:06 PM
To: mpeg-OTspec at yahoogroups.com
Subject: [mpeg-OTspec] The font top-level registration I-D

The W3C timed-text group has noted that there is no standard MIME 
name for most font formats, and that there isn't an obvious place to 
put them either.  As a result they asked me to create an I-D to 
create the top-level font/ MIME node.  A draft is included.

You'll note that we need to fill in the interoperability 
considerations, contact, and change controller for the two suggested 
top-level registrations.  However, the immediate question before the 
IETF is not these two, but the whole concept of the font/ top-level 
MIME name.

Any comments gratefully received.
David Singer
Apple Computer/QuickTime

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