I use the same Track() class that the library does. I have to create
an instance of this class each time the function is called, but this is
ok since it is not the case I am trying to optimize for.
I only want to change to gst.STATE_PLAYING or gst.STATE_PAUSED if the
pipeline currently has a file loaded. Not doing this can cause an
exception in position() when get_state() returns gst.STATE_READY instead
of gst.STATE_NULL.
