Not necessarily. A lot of video software either leverages the Windows/MacOS system codecs (ex. Media Player Classic, Quicktime) or proprietary vendor codecs (Adobe/Blackmagic).
Linux doesn't really have a system codec API though so any Linux video software you see (ex. VLC, Handbrake) is almost certainly using ffmpeg under the hood (or its foundation, libavcodec).
Linux doesn't really have a system codec API though so any Linux video software you see (ex. VLC, Handbrake) is almost certainly using ffmpeg under the hood (or its foundation, libavcodec).