The flowcombiner and active_streams shouldn't be cleared in the mse-bytestream variant, only in the mss-fragmented one. Otherwise the soft reset leaves qtdemux in a state where it still believes that it has streams, but they've been cleared. In that case, a null pointer dereference happens and the app crashes. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4199>