--------------------------------------------------------------------------------------------------------------------
// Executed by local player

@Override
public void execute(MinecraftServer server, ICommandSender sender, String[] args) throws CommandException {
    if (args.length == 2) {
        EntityPlayerMP target = (EntityPlayerMP) getEntity(server, sender, args[0]);
        if (target != null) {
            MovieMainClass.INSTANCE.sendToServer(new SendMessage("\\Movies\\" + args[1] + ".mp4"));
        }
    } else {
        return;
    }
}

--------------------------------------------------------------------------------------------------------------

// Declaration of IMessage

public static CharSequence directoryToSend = "";

    public SendMessage() {
    }

    public SendMessage(String directoryToSend) {
        this.directoryToSend = directoryToSend;
    }

    @Override
    public void toBytes(ByteBuf buf) {
        buf.writeCharSequence(directoryToSend, Charset.defaultCharset());
    }

    @Override
    public void fromBytes(ByteBuf buf) {
        directoryToSend = ((String) buf.readCharSequence(directoryToSend.length(), Charset.defaultCharset()));
    }
--------------------------------------------------------------------------------------------------------------

// Messaged recieved on server side (I believe)

@Override
public IMessage onMessage(SendMessage message, MessageContext ctx) {

    if (ctx.side == Side.CLIENT) {
        MovieMainClass.INSTANCE.sendTo(new SendMessage((String) message.directoryToSend), ctx.getServerHandler().player);
        MovieMainClass.proxy.doOverlay(message.directoryToSend.toString());
    }
    return null;
}

---------------------------------------------------------------------------------------------------------

// This is the client-side proxy

public MovieOverlay overlay;
public Thread thread;
public static String localDirectory = "";
@Override
public void doOverlay(CharSequence string) {
    try {
        // EntityPlayerSP targetPlayer = Minecraft.getMinecraft().player;
        String directory = Minecraft.getMinecraft().mcDataDir.getCanonicalPath() + string.toString();

        File f = new File(directory);

        if (f.exists()) {
                overlay = new MovieOverlay(string);
                thread = new Thread(overlay);
                thread.start();

            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }