def isES(self, file):
        file.seek(0, 0)
        try:
            header = struct.unpack('>LL', file.read(8))
        except (struct.error, IOError):
            return False

        if header[0] != 0x1B3:
            return False

        # Is an mpeg video elementary stream

        self.mime = 'video/mpeg'
        video = core.VideoStream()
        video.width = header[1] >> 20
        video.height = (header[1] >> 8) & 0xfff
        if header[1] & 0xf < len(FRAME_RATE):
            video.fps = FRAME_RATE[header[1] & 0xf]
        if (header[1] >> 4) & 0xf < len(ASPECT_RATIO):
            # FIXME: Empirically the aspect looks like PAR rather than DAR
            video.aspect = ASPECT_RATIO[(header[1] >> 4) & 0xf]
        self.video.append(video)
        return True