dashdemux: Two depth seeking for On-Demand profile

Try to find fragment using MPD first, then do refinement to find
target subframgnet using SIDX if possible. Note that, if target fragment
was moved from the previously activated one, we should assume that
the last SIDX is invalid for new fragment.

https://bugzilla.gnome.org/show_bug.cgi?id=776200
1 file changed