You can override the default librtmp buffering by setting the url to have a
param named "buffer" with the amount of latency you're targeting (see
https://rtmpdump.mplayerhq.hu/librtmp.3.html). Additionally, you can force
rtmpsrc to act as a live src with gst_base_src_set_live. Finally you can
lower the latency by disabling sync in the pipeline so that buffers are
displayed as soon as possible with total disregard for timestamps (that's
most likely not what you want, however).