def HardSub(self, input_f, output_f, sub=None):
        if sub:
            self.sub = sub
        else:
            self.sub = self.SUBF
        self.vid = input_f
        self.outname = output_f
        Subtitle(self.sub).Convert('ass')
        self.cleanup.append(self.sub+'.ass')
        res = exec_ffmpeg(['-i', self.vid, '-vf', '"ass='+self.sub+'.ass"', self.outname])
        self.doCleanup()
        if res == 1:
            self.cleanup.append(self.outname)
            self.doCleanup()
            raise Exception('Video encode error.')