FFmpeg

FFmpeg is the leading, open-source multimedia framework: it decodes, encodes, transcribes, muxes, demuxes, streams, and filters almost any audio or video format.

FFmpeg is a powerful, cross-platform command-line utility and library suite (LGPL/GPL) for processing multimedia content. The core `ffmpeg` tool handles universal format conversion—like transcoding an input MP4 to an output WebM—while bundled utilities like `ffprobe` provide deep stream analysis and `ffplay` offers simple playback. Its foundational libraries, including `libavcodec` (for codecs) and `libavformat` (for containers), support thousands of formats and protocols, making it indispensable for major platforms like YouTube and VLC for everything from real-time streaming to complex video filtering.

https://ffmpeg.org