Expect the provider to keep track of the playhead position
Previously, the position of the playhead was being added onto the buffered time both inside the HTTPVideoProvider and the model. Fixed it so that the playhead position is only added once, inside provider.
Capture seek target in HTTPVideoProvider
Instead of requiring an explicit call into the SWF to set the new starting offset for the netstream time, capture it when seekForSeconds is called in HTTPVideoProvider.