Bug#694657: closed by Reinhard Tartler <siretart at tauware.de> (Bug#694657: fixed in libav 6:9.1-1)

[Francesco Poli]

[Thanks for your fast reply, and sorry for my late reply...]


On Thu, 10 Jan 2013 18:44:11 +0100 Reinhard Tartler wrote:

> On Thu, Jan 10, 2013 at 6:30 PM, Francesco Poli
> <invernomuto at paranoici.org> wrote:
> > On Thu, 10 Jan 2013 09:55:12 +0100 Reinhard Tartler wrote:
> >
> > [...]
> >> Oh I'm sorry, I mixed that up. There is no clear answer on that
> >> because it depends. Most of the files are LGPL, but some hand-written
> >> assembler optimizations are GPL-2+. The configure script offers an
> >> --enable-gpl switch that includes those GPL-2+ sources. We do enable
> >> this switch for all packages we produce in Debian.
> >>
> >> In theory, we could probably also provide an LGPL build of libavcodec.
> >> Fortunately, nobody has requested that so far.
> >
> > Wait, are you saying that those few GPL-licensed files:
> >
> > [...]
> > |  Files: libavdevice/x11grab.c
> > |   libavfilter/yadif.h
> > |   libavfilter/vf_blackframe.c
> > |   libavfilter/vf_boxblur.c
> > |   libavfilter/vf_cropdetect.c
> > |   libavfilter/vf_delogo.c
> > |   libavfilter/vf_hqdn3d.c
> > |   libavfilter/vf_yadif.c
> > |   libavfilter/x86/yadif.c
> > |   libavfilter/x86/yadif_template.c
> > [...]
> > |  License: GPL-2+~Libav
> > [...]
> >
> > are compiled into, or linked with, each shared object (*.so) shipped in
> > all Debian binary packages built from the libav source package?
> 
> yes.
> 
> > In other words, are you saying that all binary packages built from
> > the libav Debian source package are effectively under GPL-2+
> > (except for libavcodec-extra-* and libav-dbg, which are effectively
> > under GPL-3+)?
> 
> yes.

Ouch!
This is not clear at all, by reading the debian/copyright file and/or
by looking at the binary package long descriptions!

Without intimate knowledge of the libav package build process, I just
thought that those GPL-licensed files only ended up into the binary
packages named after the directories where they live...
Without digging into all the dependencies, I hadn't noticed all the
cross linking among the binary packages built from libav...

In other words, I thought that only libavdevice and libavfilter were
under GPL-2+ and all the other libraries were separated enough to be
under LGPL-2.1+ !

Now I even notice that a number of binary packages built from libav
depend on libavcodec-extra-54, and are therefore effectively under
GPL-3+ !

I think that this should be explicitly and clearly documented in the
comment at the beginning of the debian/copyright file and, probably, in
the binary package long descriptions, as well.

> 
> > Isn't there any binary package effectively under LGPL-2.1+?
> 
> Exactly, we currently do not produce any LGPL'ed binary packages in
> Debian. In fact, we never did. Technically we could, but that would
> require significant additional complexity that I would prefer to avoid
> unless absolutely necessary.

I understand that the additional complexity is not welcome, but I
expect that a good number of people would have probably already
requested these LGPL-licensed binary packages, if the current situation
were more apparent.

Make no mistake, I am perfectly fine with a GPL-licensed library.
But:

 A) I am definitely less fine with a GPL-2-incompatible library
    (as you know, GPL-3+ is not compatible with GPL-2)

 B) it looks like a bit specious, when the library is under the GPL,
    just because of a few files

Hence, whenever the GPL-licensed files may be excluded and the linking
with other GPL-licensed libraries may be avoided, it looks like a good
idea to also provide an LGPL-licensed (reduced functionality) variant of
the library.

Sometimes you have a program under LGPL-2.1+ which links with libav* and
with a DFSG-free, but GPL-incompatible, library.
While you are trying hard to persuade the copyright holders of the
latter library to re-license under GPL-compatible terms, it would be
useful to link the program with the LGPL-licensed (reduced
functionality) variant of libav* packages, if at all possible...

Please note that this is _not_ a theoretical example: see bug #618968.

> 
> > Please clarify, since this may heavily affect the resolution of
> > licensing issues for other packages!
> 
> I imagine. I hope this mail clarifies the situation!

It does clarify, but I think the clarification should be visible to all
the interested users, not just those who happen to read this bug log.

I am therefore going to file a bug report suggesting you to clearly
document this situation.


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