Doing an instant URI change aims at changing the source asap and we
should still try to make the transition smooth. Flushing the current
source will leads to
uridecodebin3 not outputing anything while the
new URI is getting ready. Removing that flush will make the transition
smooth as we will keep using the previous source meanwhile.
I tried to discuss that on IRC but we didn't reach any conclusion. In my case I have simple RTP streams and I need to be able to smoothly switch between them. If we flush the current source while the new one is not ready (it needs to wait for keyframe before being able to do anything) the output stream freezes, keeping using the old one meanwhile seem more appropriate to me.