Libav
Libav is a complete, cross-platform solution to record, convert and stream audio and video.
Libav includes the libavcodec audio/video codec library, a decoder/encoder codec-suit that forms the basis of most free and open source software multimedia programs.
Libav also contains libavformat, a library for multimedia container formats and libavfilter for video and audio filtering, libswscale for colorspace conversion and software scaling.
Among the tools provided avplay is a simple media player, avconv is extensive tool to capture, reencode/remux and stream multimedia contents, avprobe is a quite simple information extractor.
About the Libav project
Libav is a fork of the FFmpeg project and while it doesn't share the same development practices it shares the same aims.
Libav is developed mostly under unix-like systems, but it can be compiled under most operating systems, including Microsoft Windows. The code is released adopting a seasonal major release cadence, with point releases provided when the need arises or monthly. Security releases are provided for the past 2 mayor releases and the current. Libav is free software, released under the GNU Lesser General Public License or GNU General Public License (depending on which sub-libraries one would include).