
The MP3 audio coding format
===========================

   Much has already been said about MP3 and the huge patent portfolio of
the MPEG members, especially the Fraunhofer institute. Eric Scheirer's
MPEG, Patents, and Audio Coding FAQ [1.1] is an attempt to "inject
some sanity in what is becoming an increasingly heated discussion
about patent rights surrounding MPEG technology, especially for audio
compression". It also has a few words about other patented products
covered in this document.

[1.1] http://web.media.mit.edu/~eds/mpeg-patents-faq


The AAC audio coding format
===========================

   Dolby's AAC (Advanced Audio Coding) is covered by patents owned by
Dolby Laboratories, AT&T Laboratories, Fraunhofer Institute and Sony
Corp.

   The FAAC project was threatened by the AAC license consortium. Press
report about how "an opensource project was closed down due to pressures
from the AAC license consortium which requires a lumpsum payment of
10,000 USD plus a per-copy payment of 1.35 USD, thus effectively banning
free software implementations. The policies surrounding AAC also harm
interoperability [2.2]." This was related by Heise [2.3] and FFII has
a page about the Dolby threat [2.1] as well as additional information
about MPEG-related patents [2.4].

   The author stopped distributing the FAAC binaries, but still provides
full source code and CVS access. To my knowledge he has not been
threatened again. I also read on a web forum [2.5] that Cisco's lawyers
claim that their LGPL distribution of AAC software in MPEG4IP is
completely legal and that Dolby cannot forbid such distribution.

[2.1] http://swpat.ffii.org/patents/effects/dolby/index.en.html
[2.2] http://www.xiph.org/archives/vorbis-dev/200011/0286.html
[2.3] http://www.heise.de/newsticker/data/vza-20.11.00-000/
[2.4] http://swpat.ffii.org/patents/effects/mpeg/index.en.html
[2.5] http://www.hydrogenaudio.org/index.php?showtopic=310&


The ASF file encapsulation format
=================================

   Microsoft obtained a patent on the ASF (Active Stream Format) audio
file format on March 21, 2000:

  | United States Patent 6,041,345 Levi , et al. March 21, 2000
  |
  | Active stream format for holding multiple media streams
  |
  |  Abstract An active stream format is defined and adopted for a
  | logical structure that encapsulates multiple data streams. The data
  | streams may be of different media. The data of the data streams
  | is partitioned into packets that are suitable for transmission
  | over a transport medium. The packets may include error correcting
  | information. The packets may also include clock licenses for
  | dictating the advancement of a clock when the data streams are
  | rendered. The format of ASF facilitates flexibility and choice
  | of packet size and in specifying maximum bit rate at which data
  | may be rendered. Error concealment strategies may be employed in
  | the packetization of data to distribute portions of samples to
  | multiple packets. Property information may be replicated and stored
  | in separate packets to enhance its error tolerance. The format
  | facilitates dynamic definition of media types and the packetization
  | of data in such dynamically defined data types within the format.

   This patent is rumoured to have been enforced at least once, though
only through what I'd call non-hostile intimidation. Avery Lee, the
VirtualDub author, removed ASF support from his software after a phone
call from a Microsoft employee that he relates in his 5/12/2000 news
[3.1].

   However I could not find evidence of an official threat: all I could
find on the web seemed to be interpretations of the VirtualDub author's
article, for instance on Advogato [3.2], CPT [3.3] or FFII [3.4]. Avery
Lee states that the phone call was from a programmer, not from the
legal department. There does not seem to be an official statement from
Microsoft.

[3.1] http://web.archive.org/web/20000817222620/http://www.geocities.com/virtualdub/virtualdub_news.html
[3.2] http://www.advogato.com/article/101.html
[3.3] http://www.cptech.org/ip/business/software/audio.html
[3.4] http://swpat.ffii.org/patents/effects/asf/index.en.html

