The licensing of GStreamer is no different from a lot of other libraries out there like GTK+ or glibc: we use the LGPL. What complicates things with regards to GStreamer is its plugin-based design and the heavily patented and proprietary nature of many multimedia codecs. While patents on software are currently only allowed in a small minority of world countries (the US and Australia being the most important of those), the problem is that due to the central place the US hold in the world economy and the computing industry, software patents are hard to ignore wherever you are. Due to this situation, many companies, including major GNU/Linux distributions, get trapped in a situation where they either get bad reviews due to lacking out-of-the-box media playback capabilities (and attempts to educate the reviewers have met with little success so far), or go against their own - and the free software movement's - wish to avoid proprietary software. Due to competitive pressure, most choose to add some support. Doing that through pure free software solutions would have them risk heavy litigation and punishment from patent owners. So when the decision is made to include support for patented codecs, it leaves them the choice of either using special proprietary applications, or try to integrate the support for these codecs through proprietary plugins into the multimedia infrastructure provided by GStreamer. Faced with one of these two evils the GStreamer community of course prefer the second option.
The problem which arises is that most free software and open source applications developed use the GPL as their license. While this is generally a good thing, it creates a dilemma for people who want to put together a distribution. The dilemma they face is that if they include proprietary plugins in GStreamer to support patented formats in a way that is legal for them, they do risk running afoul of the GPL license of the applications. We have gotten some conflicting reports from lawyers on whether this is actually a problem, but the official stance of the FSF is that it is a problem. We view the FSF as an authority on this matter, so we are inclined to follow their interpretation of the GPL license.
So what does this mean for you as an application developer? Well, it means you have to make an active decision on whether you want your application to be used together with proprietary plugins or not. What you decide here will also influence the chances of commercial distributions and Unix vendors shipping your application. The GStreamer community suggest you license your software using a license that will allow proprietary plugins to be bundled with GStreamer and your applications, in order to make sure that as many vendors as possible go with GStreamer instead of less free solutions. This in turn we hope and think will let GStreamer be a vehicle for wider use of free formats like the Xiph.org formats.
If you do decide that you want to allow for non-free plugins to be used with your application you have a variety of choices. One of the simplest is using licenses like LGPL, MPL or BSD for your application instead of the GPL. Or you can add a exceptions clause to your GPL license stating that you except GStreamer plugins from the obligations of the GPL.
A good example of such a GPL exception clause would be, using the Totem video player project as an example: The authors of the Totem video player project hereby grants permission for non-GPL-compatible GStreamer plugins to be used and distributed together with GStreamer and Totem. This permission goes above and beyond the permissions granted by the GPL license Totem is covered by.
Our suggestion among these choices is to use the LGPL license, as it is what resembles the GPL most and it makes it a good licensing fit with the major GNU/Linux desktop projects like GNOME and KDE. It also allows you to share code more openly with projects that have compatible licenses. Obviously, pure GPL code without the above-mentioned clause is not usable in your application as such. By choosing the LGPL, there is no need for an exception clause and thus code can be shared more freely.
I have above outlined the practical reasons for why the GStreamer community suggest you allow non-free plugins to be used with your applications. We feel that in the multimedia arena, the free software community is still not strong enough to set the agenda and that blocking non-free plugins to be used in our infrastructure hurts us more than it hurts the patent owners and their ilk.
This view is not shared by everyone. The Free Software Foundation urges you to use an unmodified GPL for your applications, so as to push back against the temptation to use non-free plug-ins. They say that since not everyone else has the strength to reject them because they are unethical, they ask your help to give them a legal reason to do so.
This advisory is part of a bigger advisory with a FAQ which you can find on the GStreamer website