[Libav-user] Clarifications about why "--use-nonfree" makes ffmpeg undistributable given the LGPL

[Phil Turmel]

On 11/26/2012 08:30 AM, Carlos Alberto Lopez Perez wrote:

> I wish to know why you think that the fact that linking ffmpeg with any
> proprietary library (or any free not-gpl compatible library) makes it
> unredistributable when the LGPL clearly says that this is allowed.

The LGPL does *not* automatically grant distribution rights to a linked
program.  There are a number of distribution conditions, with a number
of variations, all intended to make sure the end-user can practically
and legally replace the distributed library with their own modified
version, and still have a working application.

> ./configure --enable-nonfree
> [...]
> License: nonfree and unredistributable

FFmpeg can make use of resources that aren't themselves LGPL, or are
otherwise encumbered (e.g. patents).  When doing so, the compiled copy
of FFmpeg is entangled with conditions from those external resources.
The combinaton of FFmpeg's conditions with the other conditions cannot
be satisfied, so the result is undistributable.

In other words, this is a combination that an end-user must compile for
themselves.  This scenario is one of the reasons the LGPL was written to
force applications to permit relinking or its equivalent.

I am not a lawyer, though.  You might want to consult one if you don't
understand the above.

Regards,

Phil