In addition to having great flexibility over demuxer, decoder, processer, encoder, muxer choice and settings, ffmpeg can crop, stream, merge audio and video from different sources and perform many other tasks.

Easy to use once you get the hang of it.

Among the more common formats ffmpeg can handle are h.264, HEVC(h.265), mp3, AAC, mpeg-4, wmv3, ProRes, QuickTime, SWF, Speex, FLAC, VP9 and many more. To get a full list in terminal type: ffmpeg-formats

Because ffmpeg allows transcoding on the fly and supports multiple streaming protocols such as rtmp, rtsp, http, ftp, hls, you can use it to stream to services such as twitch.tv or set up your own streaming solution.

You can use both local realtime recordings or another stream as a source, transcode it if necessary, and output it to a different stream.

ffmpeg -i rtmp://server/live/originalStream -c:a copy -c:v libx264 -vpre slow -f flv rtmp://server/live/h264Stream

You can use ffmpeg to record your desktop along with audio.

There are multiple GUI implementations of ffmpeg for ease of use. Among the most commonly used WinFF (Windows, Linux), Avanti (Windows) and Miro (cross-platform) are worth taking a look at.

Licensed under LGPL.

Works on Linux, OS X and Windows.