example.py

"""
Example that shows how the new Python 2 socket client can be used.
"""

from __future__ import print_function
import time
import sys
import logging

import pychromecast
import pychromecast.controllers.youtube as youtube
import pychromecast.controllers.syno_audio as audiocontroller

#if '--show-debug' in sys.argv:
logging.basicConfig(level=logging.DEBUG)

cast = pychromecast.get_chromecast()

dsaudio = audiocontroller.DSAudioController()
cast.register_handler(dsaudio)

print()
print(cast.device)
time.sleep(1)
print()
print(cast.status)
print()

print("Media status", cast.media_controller.status)
print()

#first make sure that we are allowed to talk
dsaudio.send_identify()

time.sleep(5)
print("Sending pause command")
dsaudio.pause()
time.sleep(10)
print("Sending play command")
dsaudio.play()

syno_audio.py

"""
Controller to interface with the DS Audio-app at https://dsaudio-chromecast.synology.com/dsaudio.html
"""
from . import BaseController
import json

MESSAGE_TYPE = 'type'
MESSAGE_DATA = 'data'
MESSAGE_COMMAND = 'command'

TYPE_PLAY_INDEX = "play"
TYPE_PAUSE = "pause"
TYPE_STOP = "stop"
TYPE_PLAY = "resume"
TYPE_NEXT = "next"
TYPE_PREV = "prev"
TYPE_SEEK = "seek"
TYPE_REPEAT = "set_repeat"
TYPE_SHUFFLE = "set_shuffle"

class DSAudioController(BaseController):
    """ Controller to interact with Google media namespace. """

    def __init__(self):
        super(DSAudioController, self).__init__(
            "urn:x-cast:com.synology.dsaudio", "ED01B6D7")

    def send_identify(self):
        """ Send login request to receiver, otherwise it won't talk to us """
        self.send_message({"command": "identify"})

    def stop(self):
        """ Send stop command. """
        self.send_message({MESSAGE_COMMAND: TYPE_STOP})

    def pause(self):
        """ Send pause command. """
        self.send_message({MESSAGE_COMMAND: TYPE_PAUSE})

    def play(self):
        """ Send play command. """
        self.send_message({MESSAGE_COMMAND: TYPE_PLAY})

    def play_index(self, song_index):
        msg = {
            MESSAGE_COMMAND: TYPE_PLAY_INDEX,
            MESSAGE_DATA: {
                "playing_index": song_index
            }
        }
        self.send_message(msg)

    def next(self):
        """ Send pause command. """
        self.send_message({MESSAGE_COMMAND: TYPE_NEXT})

    def prev(self):
        """ Send play command. """
        self.send_message({MESSAGE_COMMAND: TYPE_PREV})

    def seek(self, position):
        msg = {
            MESSAGE_COMMAND: TYPE_SEEK,
            MESSAGE_DATA: {
                "position": position
            }
        }
        self.send_message(msg)

    def repeat(self, repeatMode):
        msg = {
            MESSAGE_COMMAND: TYPE_REPEAT,
            MESSAGE_DATA: {
                "mode": repeatMode
            }
        }
        self.send_message(msg)

    def shuffle(self, enableShuffle):
        msg = {
            MESSAGE_COMMAND: TYPE_SHUFFLE,
            MESSAGE_DATA: {
                "enabled": enableShuffle
            }
        }
        self.send_message(msg)


    # message handling

    def _json_from_message(self, message):
        """ Parses a PB2 message into JSON format. """
        return json.loads(message.payload_utf8)

    def receive_message(self, message, data):
        print(self._json_from_message(message))
        message_type = data[MESSAGE_TYPE]
        if message_type == "challenge":
            self._handle_challenge(data)
            return True
        elif message_type == "status":
            self._process_status(data)
            return True

        else:
           return False

    def _handle_challenge(self, data):
        challenge = data.get('data')['seed']
        msg = {
            "command": "identify",
            "data": {
                "auth_key": challenge
            }
        }
        self.send_message(msg)

    def _process_status(self, status):
        """ Process latest status update. """
        self.position = status.get('position')  # in seconds
        self.buffered = status.get('buffered')  # in seconds
        self.playing_index = status.get('playing_index')  # item in the list of songs in the album
        self.song = status.get('song')  # song object

        # 'song':{
        #    'album':'538 Dance Smash Hits 2004, Volume 4: Autumn',
        #    'type':'file',
        #    'album_artist':'Various Artists',
        #    'genre':'House/Euro House/Progressive Trance/Trance',
        #    'artist':'Marly',
        #    'composer':'',
        #    'duration':199.7406,
        #    'title':'You Never Know',
        #    'cover_url':'[url_to_cover_image]',
        #    'song_url':'[url_to_cover_image]',
        #    'extra':{
        #       'song_id':'music_4376',
        #       'ds_id':'1370LSN001554'
        #    }
        # },
        self.repeat_mode = status.get('repeat_mode')  # 'none','one','all',
        self.shuffle_enabled = status.get('shuffle_enabled')  # true, false
        self.playing_status = status.get('status')  # "playing";"pause";"stopped";
        self.seekable = status.get('seekable')  # in seconds

You could override the channel_connected method to automatically send the identify command when connected.