if (gif->loop >= 0) {
            avio_w8(pb, GIF_EXTENSION_INTRODUCER); /* GIF Extension code */
            avio_w8(pb, GIF_APP_EXT_LABEL); /* Application Extension Label */
            avio_w8(pb, 0x0b); /* Length of Application Block */
            avio_write(pb, "NETSCAPE2.0", sizeof("NETSCAPE2.0") - 1);
            avio_w8(pb, 0x03); /* Length of Data Sub-Block */
            avio_w8(pb, 0x01);
            avio_wl16(pb, (uint16_t)gif->loop);
            avio_w8(pb, 0x00); /* Data Sub-block Terminator */
        }