Initializes ffmpeg to write frames.

def __init_ffmpeg(self, image_shape):
    """Initializes ffmpeg to write frames."""
    import itertools  # pylint: disable=g-import-not-at-top
    from subprocess import Popen, PIPE  # pylint: disable=g-import-not-at-top,g-multiple-import,g-importing-member
    ffmpeg = "ffmpeg"
    height, width, channels = image_shape
    self.cmd = [
        ffmpeg, "-y",
        "-f", "rawvideo",
        "-vcodec", "rawvideo",
        "-r", "%.02f" % self.fps,
        "-s", "%dx%d" % (width, height),
        "-pix_fmt", {1: "gray", 3: "rgb24"}[channels],
        "-i", "-",
        "-filter_complex", "[0:v]split[x][z];[x]fifo[w];[z]palettegen,fifo[y];"
                           "[w][y]paletteuse,fifo",
        "-r", "%.02f" % self.fps,
        "-f", self.file_format,
        "-qscale", "0",
        "-"
    ]
    self.proc = Popen(
        self.cmd, stdin=PIPE, stdout=PIPE, stderr=PIPE, bufsize=-1
    )
    (self._out_thread, self._err_thread) = itertools.starmap(
        self._start_reader_thread, [
            (self.proc.stdout, self._out_chunks),
            (self.proc.stderr, self._err_chunks)
        ]
    )