dashdemux: Nominal bitrate is estimated rather than set from selected stream
Submitted by Jonathan Miles
adaptivedemux sets GST_TAG_NOMINAL_BITRATE to stream->fragment.bitrate. If fragment.bitrate isn't set by the subclass, it will calculate a bitrate based on fragment size and duration.
As dashdemux doesn't set fragment.bitrate, and the fragments vary in size, this means that the nominal bitrate for DASH playback varies and doesn't reflect the headline bitrate of the selected stream.