[cc-community] CC-BY-SA -> GPLv3+ and work compatibility with those licences

Maciej Pendolski beholder0x100 at gmail.com
Sun Dec 25 06:05:03 EST 2011

A CC-BY-SA work "exported" to GPL might or might not be compliant with
GPL. E.g. if someone releases an electronic music album in a form of
an audio file which is then "exported" to GPL, it will [most likely]
not be a valid GPL-licenced work.

IMO the "preferred form of the work for making modifications to it"
(Source Code) for such music album (if created using e.g. LMMS or
Rosegarden) would be a project file with MIDI/... notes, information
about what effects have been used, with what parameters, what
synthesisers, automation tracks, samples, ... GPL would require a
person who have decided to use CC-BY-SA work under GPL to release
Source Code and if it (the Source Code) would not be available under
same CC-BY-SA licence (or directly under GPL) then GPL version could
not exist / would not be valid.

Of course it makes sense that not everything can be injected into
GPL'ed works. The problem is that some people might wrongfully assume
that just because CC-BY-SA work can be used under GPL, that work will
be perfectly valid under terms of GPL. So first of all a CC-BY-SA work
(and "sub-works") would not have to opt out from GPL "compatibility"
and then someone would have to make an analysis (for a given
medium/format or for a specific case) to tell if GPL compatibility is
possible at all (without having to ask all contributors to release
their Source Code (even then it could be hard to determine what a
Source Code is)).

Perhaps this could lead to some conflicts. One group claiming that the
work is GPL-compatible, the other group claiming it is not. E.g. how
should photos be treated? What is a preferred form of modification? Is
it just some high-quality jpeg file? Or should it be raw,
multiple-exposition (if available), at original resolution, with no
lossy compression? In both cases the work is approximately same (and
both forms would be usable) but some people could "demand" to have
everything (raw, ...) as a specific transformation they wish to
perform (e.g. heavy post-processing) could lead to much lower quality
when using jpeg file as a base. Some groups could decide against use
of works which they can't clearly label as being compatible with GPL.

GPLv3 also states:
"6. Conveying Non-Source Forms.
You may convey a covered work in object code form under the terms of
sections 4 and 5, provided that you also convey the machine-readable
Corresponding Source under the terms of this License"
"The “Corresponding Source” for a work in object code form means all
the source code needed to generate, install, and (for an executable
work) run the object code and to modify the work, including scripts to
control those activities. However, it does not include the work's
System Libraries, or general-purpose tools or generally available free
programs which are used unmodified in performing those activities but
which are not part of the work."

So in a case of a music album audio file release a "source code needed
to generate" would mean a project file. If a project file would be
understood by "generally available free programs" then a source code
used to "modify the work" would not have to be released (what about
synthesisers?). But what if no tool other than some proprietary
tool(s) would exist for project file modification?

Perhaps even today some game/multimedia/... content is GPL'ed in an invalid way?

My concern is that CC-BY-SA -> GPL might not be used in many projects
which could benefit from this feature of CC-BY-SA 4.0 (if it would be
implemented) because of those uncertainties.

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