OBS uses FFmpeg for media source playback, some audio encoders, and specific video output contexts. Usually FFmpeg isn't used for video encoding, though -- that

OBS uses FFmpeg for media source playback, some audio encoders, and specific video output contexts. Usually FFmpeg isn't used for video encoding, though -- that's handled by either a direct hardware encoder implementation or by a native x264 encoder (i.e. not FFmpeg's x264 implementation). OBS supports FFmpeg output in Advanced mode, but it's by no means the default.