private void writeGraphicControlBlock(OutputStream os, int delay, int transparent_color, int disposalMethod, int userInputFlag) throws Exception {
    	// Scale delay
    	delay = Math.round(delay/10.0f);
    	
        byte[] buf = new byte[8];
		buf[0] = EXTENSION_INTRODUCER; // Extension introducer
		buf[1] = GRAPHIC_CONTROL_LABEL; // Graphic control label
		buf[2] = 0x04; // Block size
		// Add disposalMethod and userInputFlag
		buf[3] |= (((disposalMethod&0x07) << 2)|((userInputFlag&0x01) << 1));
		buf[4] = (byte)(delay&0xff);// Delay time
		buf[5] = (byte)((delay>>8)&0xff);
		buf[6] = (byte)transparent_color;
		buf[7] = 0x00;
		
		if(transparent_color >= 0) // Add transparency indicator
			buf[3] |= 0x01;
		
		os.write(buf, 0, 8);
	}
Write out a zero length data sub-block
subs/gif-revert/src/main/java/com/engineer/gif/revert/lib/AnimatedGIFWriter.java