mpv
mpv is a free, open-source, and cross-platform media player that focuses on high-quality playback, extensive format support, and a minimalistic user interface. It is based on the MPlayer and mplayer2 projects, offering advanced features like GPU-accelerated video decoding, scripting support, and a command-line interface for automation and customization.
Developers should learn mpv when they need a lightweight, highly customizable media player for testing video/audio playback in applications, automating media workflows, or building media-centric tools. It is particularly useful for handling diverse media formats, integrating with scripts via its IPC (Inter-Process Communication) or Lua scripting, and for use in headless environments where GUI-based players are impractical.