After our two-day break as requested by Jean, I thought I'd look for
something definitive about the question raised by Karsten.
I haven't found any cases where this question has been adjudicated, so we
don't have the court's opinion on this.
However, the FSF has been active in defending Free Software, and created
the GPL 3.0, the AGPL 3.0, and LGPL 3.0 in response to court cases and user
behavior. And I think you would be hard-pressed to find anybody who is
stronger in terms of asserting "copyleft" than the FSF.
With that in mind, I find these the answers to these two questions in the
FSF GPL 3.0 FAQ to be clear, convincing, and certain that there is no
mechanism by which GPL 3.0 applied to LilyPond or OLL can result in GPL
requirements for LilyPond output.
[see https://www.gnu.org/licenses/gpl-faq.en.html#WhatCaseIsOutputGPL ]
Is there some way that I can GPL the output people get from use of my
program? For example, if my program is used to develop hardware designs,
can I require that these designs must be free? (#GPLOutput
<https://www.gnu.org/licenses/gpl-faq.en.html#GPLOutput>)
In general this is legally impossible; copyright law does not give you any
say in the use of the output people make from their data using your
program. If the user uses your program to enter or convert her own data,
the copyright on the output belongs to her, not you. More generally, when a
program translates its input into some other form, the copyright status of
the output inherits that of the input it was generated from.
So the only way you have a say in the use of the output is if substantial
parts of the output are copied (more or less) from text in your program.
For instance, part of the output of Bison (see above) would be covered by
the GNU GPL, if we had not made an exception in this specific case.
You could artificially make a program copy certain text into its output
even if there is no technical reason to do so. But if that copied text
serves no practical purpose, the user could simply delete that text from
the output and use only the rest. Then he would not have to obey the
conditions on redistribution of the copied text.
In what cases is the output of a GPL program covered by the GPL too? (
#WhatCaseIsOutputGPL
<https://www.gnu.org/licenses/gpl-faq.en.html#WhatCaseIsOutputGPL>)
The output of a program is not, in general, covered by the copyright on the
code of the program. So the license of the code of the program does not
apply to the output, whether you pipe it into a file, make a screenshot,
screencast, or video.
The exception would be when the program displays a full screen of text
and/or art that comes from the program. Then the copyright on that text
and/or art covers the output. Programs that output audio, such as video
games, would also fit into this exception.
If the art/music is under the GPL, then the GPL applies when you copy it no
matter how you copy it. However, fair use
<https://www.gnu.org/licenses/gpl-faq.en.html#GPLFairUse> may still apply.
Keep in mind that some programs, particularly video games, can have
artwork/audio that is licensed separately from the underlying GPLed game.
In such cases, the license on the artwork/audio would dictate the terms
under which video/streaming may occur. See also: Can I use the GPL for
something other than software?
<https://www.gnu.org/licenses/gpl-faq.en.html#GPLOtherThanSoftware>
Having this strong statement from the FSF, I feel no need to worry about
losing my music to the GPL. If anybody has case law where this principle
is violated, I would be happy to hear it.
Thanks,
Carl
As far as I understand, David K. expressed that merely calling the
functionality has no implications. Getting a definite source for this
would be great because I do see the potential concerns with this
question; after all it would be different from linking to library
compiled from, say, C code under the GPL.