Filter by src host and length

[ghost]

Hi, I am trying to filter the traffic using this syntax but it's throwing me an error when I try to run it.

const interface = 'en0';
let filter = 'src host xxx.xx.xx.xx \\udp';
const pcap = require('pcap'),
  pcap_session = pcap.createSession(interface, filter);


pcap_session.on('packet', function (raw_packet) {
  let packet = pcap.decode.packet(raw_packet);
  console.log(packet);
  console.log('======================');
});

This error :

this.link_type = this.session.open_live(this.device_name, this.filter, this.buffer_size, this.outfile, packet_ready, this.is_monitor);
Error: syntax error in filter expression: syntax error

I've looked at the man of pcap-filter and they say :

src host host
True if the IPv4/v6 source field of the packet is host.

Have I done something wrong ? or how can I only listen to udp package where the src host is a specific id ?

NB: I also try to add a "greater 1200" in the filter but it gives me a syntax error as well. How can I do that ?

Thanks !