Most files in FFmpeg are under the GNU Lesser General Public License version 2.1 or later (LGPL v2.1+). Read the file
COPYING.LGPLv2.1 for details. Some other files have MIT/X11/BSD-style licenses. In combination the LGPL v2.1+ applies to FFmpeg.
Some optional parts of FFmpeg are licensed under the GNU General Public License version 2 or later (GPL v2+). See the file
COPYING.GPLv2 for details. None of these parts are used by default, you have to explicitly pass
--enable-gpl to configure to activate them. In this case, FFmpeg's license changes to GPL v2+.
Specifically, the GPL parts of FFmpeg are:
vf_lensfun.c(GPL version 3 or later)
Should you, for whatever reason, prefer to use version 3 of the (L)GPL, then the configure parameter
--enable-version3 will activate this licensing option for you. Read the file
COPYING.LGPLv3 or, if you have enabled GPL parts,
COPYING.GPLv3 to learn the exact legal terms that apply in this case.
There are a handful of files under other licensing terms, namely:
libavcodec/jrevdct.care taken from libjpeg, see the top of the files for licensing details. Specifically note that you must credit the IJG in the documentation accompanying your program if you only distribute executables. You must also indicate any changes including additions and deletions to those three files in the documentation.
tests/reference.pnmis under the expat license.
FFmpeg can be combined with a number of external libraries, which sometimes affect the licensing of binaries resulting from the combination.
The following libraries are under GPL version 2:
When combining them with FFmpeg, FFmpeg needs to be licensed as GPL as well by passing
--enable-gpl to configure.
The following libraries are under LGPL version 3:
When combining them with FFmpeg, use the configure option
--enable-version3 to upgrade FFmpeg to the LGPL v3.
The VMAF, mbedTLS, RK MPI, OpenCORE and VisualOn libraries are under the Apache License 2.0. That license is incompatible with the LGPL v2.1 and the GPL v2, but not with version 3 of those licenses. So to combine these libraries with FFmpeg, the license version needs to be upgraded by passing
--enable-version3 to configure.
The smbclient library is under the GPL v3, to combine it with FFmpeg, the options
--enable-version3 have to be passed to configure to upgrade FFmpeg to the GPL v3.
There are certain libraries you can combine with FFmpeg whose licenses are not compatible with the GPL and/or the LGPL. If you wish to enable these libraries, even in circumstances that their license may be incompatible, pass
--enable-nonfree to configure. This will cause the resulting binary to be unredistributable.
The Fraunhofer FDK AAC and OpenSSL libraries are under licenses which are incompatible with the GPLv2 and v3. To the best of our knowledge, they are compatible with the LGPL.