17. Baseline Media Formats

Editor

Philipp Hoschka ([email protected]), (W3C)

17.1 Introduction

This Section defines a number of baseline media formats that the members of the W3C SYMM Working Group believe will be widely supported by SMIL players. Authors are encouraged to encode media objects in these formats to ensure that their SMIL documents can be played back by a wide range of SMIL implementations. Often, for audio and video formats, the baseline formats will be used as fallbacks when a player cannot render a more efficient, but less widely supported format. This can be achieved by using a switch element as shown in the following example:

<switch>
  <audio src="non-baseline-format-file" />
  <audio src="baseline-format-file" />
</switch>

Note that this Section is non-normative, and that thus implementation of the baseline formats is not a precondition for conformance to this specification.

For selecting the baseline formats, the following criteria were used:

• Implementing the format should not reqire a license fee OR
• The format should be implemented on a wide variety of platforms, indicating that licenses are available on reasonable and non-discriminatory terms. The platforms reviewed were the Linux operating system, the Java Media framework, Apple Quicktime, RealNetworks RealMedia and Microsoft Windows Mediaplayer multimedia platforms, and the Netscape and Internet Explorer browsers (trademarks are poperty of their respective owners).

17.2 Audio Formats

• audio/basic [MIME-2]

  @@ defined as follows: The content of the "audio/basic" subtype is single channel audio encoded using 8bit ISDN mu-law [PCM] at a sample rate of 8000 Hz. Note that this is probably a subset only of .au - need a spec for .au.

  Bandwidth: 64 Kbit/s

Editor's note: The Working Group encourages information on other audio formats that have lower bandwidth requirements than audio/basic and also do not require a license fee.

@@@ all the following "support" lists will not go in the final version

Support:

• Linux: yes (reference ?)
• Java Media: yes
• Quicktime: yes
• RealMedia: yes for .au (@@ confirm .au is a superset of audio/basic)
• MS Windows Media: yes for au (@@ but only if "local")
• Internet Explorer: yes
• Netscape: yes

@@ efforts to come up with license-free audio codecs

• preliminary effort to develop IP free audio compression format
• Ogg Vorbis CODEC project

17.3 Image Formats

• image/png ([PNG-MIME], [PNG-REC])

  Support:

  • Linux: yes
  • Java Media:no (but maybe in Java ?)
  • Quicktime: yes
  • RealMedia: yes (reference ?)
  • MS Windows Media: no
  • Internet Explorer: yes (reference ?)
  • Netscape: yes (reference ?)

• image/jpeg ([MIME-2], [JFIF])

  Support:

  • Linux: yes
  • JavaMedia: yes, supported in Java without Java Media Framework
  • Quicktime: yes
  • RealMedia: yes (baseline only, no support for progressive JPEG and grayscale)
  • MS Windows Media: no
  • Internet Explorer: yes
  • Netscape: yes

17.4 Video Formats

• video/mpeg [MIME-2]
  @@ MIME type definition is unclear, supposedly, this is MPEG-1 video - is there a spec for a file format for this ?

  @@ are there licensing requirements for MPEG-1 ? The availability of Linux code would tend to suggest there aren't.

  Support:

  • Linux: yes
  • Java Media: yes
  • Quicktime: yes (Mac only, not on Windows)
  • RealMedia: yes, via plugin
  • MS Windows Media: yes
  • Internet Explorer: @@
  • Netscape: @@
• video/quicktime ([QT-MIME], [QT])

  @@ should restrict to one track and one codec, e.g motion JPEG or Cinepak

  Support:

  • Linux: yes (?? Supported video is MJPA, JPEG Photo, PNG, RGB, YUV 4:2:2, and YUV 4:2:0 compression)
  • Java Media: yes (Cinepak, H.261, H.263, Indeo (iv31 and iv32), JPEG (411, 422, 111), RGB)
  • Quicktime: yes
  • RealMedia: G2 on Windows supports CVID, Cinepak, and Indeo codec compression, provided those codecs are installed on the machine already.
  • MS Windows Media: yes, supports version 2 and lower (@@ check which codecs)
  • Internet Explorer: @@
  • Netscape: @@

Editor's note: The Working Group encourages information on other video formats that have lower bandwidth requirements that do not require a license fee.

17.5 Text Formats

• text/plain [MIME-2]

  For profiles supporting SMIL layout, players must choose a font size so that the constraints expressed by the fit attribute of the region element associated with the media object are fulfilled. If there is no associated region element, @@@ all bets are off, since text has no intrinsic size.

  @@ need to provide interpretation for "fit" attribute for objects without intrinsic size
  @@ suggestion to use CSS proposal for "copyfitting" (@@ pointer ?)

  @@ suggestion to use generic CSS font names, see http://www.w3.org/TR/REC-CSS2/fonts.html#generic-font-families

  @@ suggestion to require CSS support for text/plain

• text/html @@ with appropriate parameter ? XHTML WG needs to decide about MIME type for XHTML profiles

  XHTML profile consisting only of the basic modules �[XMOD] "Structure" (contains e.g. html and body element), "Basic Text" (contains e.g. p and h1 element), "Hyptertext" (contains a element) and "List" (contains e.g. ul and li elements). The elements in this profile should be formatted using the "Mosaic-style" formatting described in CSS2 (@@ this means that the formatting is mostly fixed, and that there is no need to support CSS).

@@ Auxiliary links

• Supported file formats in Quicktime
• Supported content formats Windows media player
• RealNetworks authoring guide (contains list of supported formats)
• Supported media formats Java Media Framework 2.0 reference implementation