GStreamer is developed under the terms of the LGPL (see LICENSE file for details). Some of our plugins however rely on libraries which are available under i other licenses. This means that if you are using an applications which has a non-GPL compatible license, for instance a closed-source application with GStreamer you have to make sure not to use GPL linked plugins.
When using GPL linked plugins GStreamer is for all practical reasons under the GPL itself. 

The plugins which use a GPL library are as follows:
cdparanoia      libcdparanoia   (http://www.xiph.org/paranoia/)
aasink		aalib		(http://aa-project.sourceforge.net/aalib/)
xmms		libxmms		(http://www.xmms.org)
decdvd		ac3dec,mpeg2dec	(http://linuxvideo.org/mpeg2dec/,http://linuxvideo.org/ac3dec/)a

Plugins which use library a LGPL are as follows:
Colorspace 	Hermes 		(http://www.clanlib.org/hermes/)
httpsrc		libghttp	(ftp.gnome.org/pub/GNOME/stable/sources/libghttp/)
alsasink	alsa		(http://alsa-project.org)
aRts		aRts		(http://arts-project.org)
sdlsink		libsdl		(http://www.libsdl.org)
gnomevfssource  gnome-vfs       (ftp.gnome.org//pub/GNOME/stable/sources/gnome-vfs)
gnomevfssink    gnome-vfs
esdsink         libesd          (ftp.gnome.org/pub/GNOME/stable/sources/esound)
icastsend       libshout        (http://www.icecast.org)
lame            libmp3lame      (http://www.mp3dev.org/mp3/)
gst1394         libraw1394      (http://linux1394.sourceforge.net)
flac		libFLAC		(http://flac.sourceforge.net)
RTP		ortp		(http://www.linphone.org/ortp/)

Plugins which use a BSD covered library are as follows:
vorbisenc	libogg/libvorbis	(http://www.xiph.org/ogg/vorbis)
vorbisdec	libogg/libvorbis

Plugins based on libraries with other free licenses:
xsink		libXv		(MIT X11 / X Consortium license)
gsm		libgsm		(MIT license http://kbs.cs.tu-berlin.de/~jutta/toast.html)

Plugins using non-free libraries:
xamp3 decoder 	libxaudio       (http://www.xaudio.com/)
wincodec	win32ddl	(http://divx.euro.ru/)