#FFmpeg is the leading multimedia framework.
https://ffmpeg.org/
#MLT is an open source multimedia framework, designed and developed for television broadcasting.
https://www.mltframework.org/
#GPAC is an open-source multimedia framework designed for research and development.
https://gpac.io/
#MEncoder is a command-line video encoding tool that is part of the MPlayer project.
http://www.mplayerhq.hu/
#GStreamer is a pipeline-based multimedia framework.
https://gstreamer.freedesktop.org/