The Dirac software source code is licenced under the
Mozilla Public License Version 1.1. A plain text version
of this licence is available in
copying.txt. Much more detail may be found at Mozilla & Netscape
Public licences. Legal documents can be difficult for
non-lawyers to read. An annotated version of the licence
is available at
Mozilla & Netscape Public licences that contains
informal explanations of various sections of the licence.
The provisions of the Mozilla Public License allow for
relicensing under other licences that are specified in
the licence preamble at the beginning of each source-code
file. For the Dirac project the licences under which
relicensing is possible are specified to be the GNU
General Public License Version 2.0 and the GNU Lesser
General Public License Version 2.1. These may be
downloaded from GNU;
copies are also provided in Annex A and Annex B of
copying.txt. The rationale for allowing re-licensing
under GPL & LGPL is to permit the widest possible use
of this technology whist retaining the advantages of the
MPL license.
The Dirac approach to licensing
We wish Dirac to be used as widely as possible, royalty
free. We thought long and hard in selecting the MPL
version 1.1 (hereafter simply the MPL) as the licence for
Dirac. We chose it because it's a well-known and widely
used licence, and also because it contains practical
provisions for dealing with patent issues in what is a
highly patented field.
As a defensive measure the BBC has applied for patent
protection for some techniques that are, or may be, used
within Dirac. Our purpose in doing so is to provide
protection for Dirac from spurious patent suits by other
parties. Under the terms of the MPL we have licensed
these patents irrevocably and royalty free for use within
the Dirac software. Our aim is to increase the likelihood
that Dirac succeeds, and is used.
However, no licence can grant rights to use third-party
patents that are not owned by the licensor. This problem
applies to all technologies, whether proprietary, Open
Source, or (as illustrated in the case of JPEG) Open
Standards, and is a risk that is faced by everyone. We're
working hard to avoid using third-party patents
altogether, and this is one reason why the Dirac
algorithm may yet change. The licence itself cannot
address this issue.
Our intention is that Dirac code be used as widely and as
freely as possible. This is why we have allowed
re-licensing under the terms of the GPL and LGPL
licences. Had we not allowed this, as alternative
licences under the MPL, GPLed projects could not have
used the Dirac software. The option to re-license under
the LGPL allows even commercial software to link to Dirac
libraries. With the re-licensing provision in the MPL,
GPL and LGPL projects may use the Dirac software as is.
In this case the patent licence granted under the MPL
still applies explicitly. Some projects may prefer to
ensure that all their code is distributed only under the
GPL or LGPL licence. This is also permitted under the MPL
licence. If a project does this then the usual provisions
of the GPL or LGPL licence applies and these simply do
not involve patent issues (they relate only to
copyright). However, in practice, users are still free to
use the BBC patents royalty free.
Our philosophy is that the Dirac licence is merely a tool
to allow people to use and work on Dirac: the licence is
not a complete expression of our commitment to Dirac. The
MPL does have some limitations, but it was our view that
it was better to use a licence that did most of what we
wanted than invent a new one that might be viewed with
suspicion and which would not have been subject to the
same level of scrutiny as the MPL. If we find that the
MPL is an impediment to free and open use of Dirac then
we will be happy to consider using alternative or
additional licences to achieve its widespread, royalty
free use.
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