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Re: MP3 decoder packaged with XMMS

Presumably you are also aware of patents 5,341,457 and 5,627,938,
which Lucent has been seeking to enforce against Dolby AC-3.  As your
encoder appears to use Ehmer's tone masking techniques, which are also
cited in the AC-3 standard definition, that litigation may be of
interest -- particularly as Dolby obtained in April a summary judgment
of non-infringement and there is a real possibility that Lucent's
patents will be invalidated altogether if the remainder of the case
goes to trial as scheduled in September.

Although your psy.c is a bit opaque and I have given these Lucent
patents only the briefest of glances, I would say that the '457 patent
disclosure resembles the Vorbis encoder more closely than anything
else I have seen in the literature.  No suggestion that you infringe
is implied; I'm just trying to get a handle on how psy.c works and the
patent database is the best hook into the primary literature that I am
currently holding.

I haven't identified which, if any, patents cover Dolby AC-3 qua AC-3
(that's a Dolby trademark, as is Dolby Digital 5.1; the generic name
is "ATSC Standard A/52").  There seems to be a relevant patent pool in
DVD space (in which Dolby participates, to the extent of receiving a
small royalty on AC-3 encoded DVDs, but may not have contributed any
patents AFAICT).  There is an interesting list in Appendix A of
http://contracts.onecle.com/intervideo/dolby.lic.1999.03.04.shtml but
I haven't ground through it and probably won't.

The "cease and desist" letter at
http://www4.netbsd.org/Letters/20010803-dolby.html looks to me to be
"actual notice" of nothing whatsoever.  Given that Dolby approaches
"violators" even more prejudicially than Thomson does (or used to?),
somehow I suspect that if Dolby had a leg to stand on other than their
trademarks then there would be some record of their citing a specific
patent against A52dec and/or FFmpeg (which remain on SourceForge). 

I have, however, tracked down the principal DTS patent (#5,956,674)
claimed against VideoLan's libdca; but it has such a thicket of claims
that I cannot begin to say what might or might not infringe it other
than an implementation of DTS itself.  I doubt they would bother you,
though; their format is wildly different (mixed VQ and ADPCM,
specialized subframes to massage transients away, "signal-to-mask
ratios"), and it has the general air of a tweak of a hack to a kludge.
 So, by reputation, does AC-3; so unless Dolby holds something pretty
general (which would surprise me), it also seems unlikely to threaten
Vorbis unless you know something I don't.

- Michael

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