FFmpeg is a free and open-source software project consisting of a suite of libraries and programs for handling video, audio, and other multimedia files and streams. At its core is the command-line ffmpeg tool itself, designed for processing of video and audio files. It is widely used for format transcoding, basic editing (trimming and concatenation), video scaling, video post-production effects and standards compliance (SMPTE, ITU).

FFmpeg also includes other tools: ffplay, a simple media player and ffprobe, a command-line tool to display media information. Among included libraries are libavcodec, an audio/video codec library used by many commercial and free software products, libavformat (Lavf),8 an audio/video container mux and demux library, and libavfilter, a library for enhancing and editing filters through a Gstreamer-like filtergraph.9

FFmpeg is part of the workflow of many other software projects, and its libraries are a core part of software media players such as VLC, and has been included in core processing for YouTube and Bilibili.10 Encoders and decoders for many audio and video file formats are included, making it highly useful for the transcoding of common and uncommon media files.

FFmpeg is published under the LGPL-2.1-or-later or GPL-2.0-or-later, depending on which options are enabled.11

Source: Wikipedia