First, the xing header frame is never added to the count,
we have to increment the count.
Secondly, there is a rounding error when calculating the
frame duration, as spf*GST_SECOND/rate is not an integer
(26122448.9) an it must be 26122449.
It's been replaced by mpegaudioparse in -good. Don't want anyone
to spend time porting a deprecated element. Rename plugin to xingmux
for now until we move that somewhere else.
