Use the bitrate advertised by queue2 to determine the limits to
set across possibly multiple queue2/downloadbuffer elements. e.g.
with two queue2's and a max-bytes based on the ratio of the
bitrate/cumulative_bitrate multiplied by the buffer_size set on urisourcebin.
This allows finer grained control over the buffer used by all the queue
elements inside urisourcebin. Instead of a maximum of
n_streams*buffer_size being used, only buffer_size will be used however
we will fallback to n_streams*buffer_size if one of the queue2's does
not have bitrate information.
https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/issues/60
8b69b689c0