qtmux: Allow configuring trak timescale per pad/trak

It generally makes not much sense to configure it for all pads/traks at
once as this value is usually different for each of them. As such, add a
new property on the pads in addition to the existing property on the
whole muxer.

https://bugzilla.gnome.org/show_bug.cgi?id=792649
1 file changed