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In addition to having great flexibility over demuxer, decoder, processer, encoder, muxer choice and settings, GStreamer can clip, crop, stream, extract frames, merge audio and video from different sources and perform many other tasks.
You can dynamically load plugins and implement different libraries to extend functionality.
Pro Excellent debugger
GStreamer can give you detailed information about the pipeline and each individual process it's running.
Pro Excellent variety of formats
Among the more common formats GStreamer can handle are h.264, HEVC(h.265), mp3, AAC, mpeg-4, wmv3, ProRes, QuickTime, SWF, Speex, FLAC, VP9 and it can also be extended with other libraries to support different formats.
Pro Free and open-source
Licensed under LGPL.
Available on Windows, OS X, and Linux.