def duration(self):
        # calc size of clip in secconds
        # may be size of raw, but take into account trimming start/end
        def to_sec(time, default=0):
            # convert h:m:s to s
            if time:
                sec = reduce(lambda x, i: x*60 + i,
                    list(map(float, time.split(':'))))
            else:
                sec=default
            return sec
        start = to_sec( self.start )
        end = to_sec( self.end, to_sec(self.raw_file.duration))
        dur = end-start
        return dur