Flutter Screencast

Summary

Nowadays castscreen from a phone to a TV is pretty easy, you can use chrome-cast to handle most of android-devices(except these tvs of China). But sometimes you need to use DLNA protocol.

tips: in China, you can also use lelink sdk(https://cloud.hpplay.cn/)

so today we will use DLNA protocol to cast videos to an android TV.

to know more about DLNA, please read DLNA conception.

Pros and cons of using DLNA protocol

Pros

• no cost, except time and brain
• as DLNA is an open-source protocol, it is supported by most of the TVs

Cons

• different device maybe have different configurations and commands
• write a lot of code( compared to other chrome/lelink sdk)
• maybe hard to debug

Steps

1. search devices

To search a DLNA device, we need to use Simple Service Discovery Protocol(ssdp), which is a UDP protocol.

The code is like this:

final socket = await RawDatagramSocket.bind(address, port);
_sockets.add(socket);

socket.listen((event) {
    if (event == RawSocketEvent.read) {
    final packet = socket.receive();

    if (packet == null) return;

    final data = utf8.decode(packet.data);
    final headers = data.split('\r\n');

    if (headers.indexWhere((e) => e.contains('HTTP/1.1 200 OK')) == -1) {
        return;
    }

    _addDevice(headers);
    }
});

in the code above, address is an InternetAddress type, we use a function to get it:

InternetAddress _getBroadcastAddress(InternetAddressType addressType) {
    switch (addressType) {
      case InternetAddressType.IPv4:
        return InternetAddress.anyIPv4;
      case InternetAddressType.IPv6:
        return InternetAddress.anyIPv6;
      default:
        throw ArgumentError("Internet Address Type not valid");
    }
  }

this means we will bind to any ipv4 or ipv6 address.

to be continued…