GStreamer doesn’t use ffmpeg’s pipeline at all. It implements a much more advanced directed graph with disconnect, connection and pad negotiation. You can dynamically swap out the entire filter graph during live playback with zero disruption. Swap feeds, outputs, effects… all at runtime.

ffmpeg and other media frameworks (Windows Media Foundation, Apple’s AVFramwork) only support static pipelines. You can use “switcher” components but the inputs are still static.

GStreamer is extremely special. The only thing that comes close was Microsoft’s DirectShow, which has since been replaced with Media Foundation which can’t do it. And while DirectShow did support it, it was fragile because many 3rd party filters did not support dynamic configuration.

GStreamer does use ffmpeg, but it just wraps the core encoder/decoder/filter code and discards the streams/graph/pipe part of ffmpeg.