As vanilla as it gets, cast a YouTube (or custom) video to a Chromecast
As vanilla as it gets, cast a youtube (or custom) video to a chromecast without any dependencies (No Google or Google-ProtoBuf libs required)
None! this script is written in pure vanilla Python 3+.
python chromecast.py <ip to chromecast> <YouTube video id>
For instance:
python chromecast.py 192.168.0.10 ZTidn2dBYbY
Or feed a custom mp4 URL to the script (Currently mp4 is a hardcoded header until I figure something out):
python chromecast.py 192.168.0.10 http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4
Note: To find your chromecasts, you can use avahi-browse -tr _googlecast._tcp or nmap --open -sS -Pn -n -p 8009 192.168.0.0/24 (Replace the subnet with your own and look for 8009/tcp open).
Two things. The first being - just use pychromecast or casttube. They’re more fully fledged.
Secondly, Google heavily uses their open protocol called protobuf.
It’s essentially just a struct -> bytes serializer. I’ve included a very crude serializer & de-serializer for sending and reading protobuf streams. A quick overview of how that works would be:
Variable type overview:| <field ID> | <Variable Type> | <Variable Data> |
Below are two examples describing the most common variables found in a chromecast session.
INT variables with a field ID of 5:
| 00101 | 000 | 0001 1000 |
The value of this integer would be 24, and it’s up to the developer to define what field 5 should be.
In chromecast world, that’s payload_type, so that would normally have a int value of 0 for utf8 string payload.
string example with a payload and field ID of 3:
| 00011 | 010 | 0001 0011 | {"type": "CONNECT"}
The field ID (00011) is 3. And the variable type (010) is string.
The length of the string is the next byte, which in this case is 19 (0001 0011).
The payload is {"type": "CONNECT"}. That’s the basics of ProtoBuf.
Chromecast has a set of fields that needs to be defined in a ProtoBuf format.
Those fields are:
::int::str::str::str::int::strAnd the order is very important. Because the field_id is in the data stream and they need to come in a certain order to match on both sides.
The names however can be anything, but the type - meaning - and order is important.
But the names are just for your convenience and you can decide to name them whatever you want.
Protocol version just tells chromecast which protocol to talk. Currently that’s v2.1.0 which is represented by the int 0. So a lonely ZERO (0) defines that.
Source ID is the sender (or caster’s) id. This can probably (!?) be anything you want.
But in reality the magic keyword of sender-0 seams to do the trick.
This field changes depending on what casting-state you’re in.
It starts off with the magic keyword of receiver-0 but once an application has been launched,
this should be changed to whatever the instance-id is of that application - letting the chromecast know you’re talking to the application and not the chromecast.
There’s also a magic keyword Tr@n$p0rt-0 which feels like an odd design choice. But is used by the chromecast to send heartbeat information in the shape of {"type":"PING"} with the sender and receiver-id’s being Tr@n$p0rt-0. Not sure why, seams like an odd implementation thing.
Namespace is the URN (or URI/URL if you’re more familiar with those terms) in which you want to call or talk to. Lets say you want to talk to the YouTube app, you need a namespace URN of: urn in order to let the chromecast know you want to talk to the YouTube app. All applications have their own URN’s, and I don’t know how you can find those other than finding URN’s in other libraries or listening for the 
com.google.youtube.mdxnamespaces response when launching an app (which requires you to know an app ID to launch).
The payload type can be two different types, either bytes or utf8 strings. I think chromecast supports both. But sticking to utf8 strings are quite simple and works for most cases talking to the youtube and the generic media app heh. So keep the type 0 for utf8 strings (1 for bytes payloads as a reference).
The payload contains the actual data being sent back and fourth for parsing.
For instance, the {"type": "CONNECT"} payload is meant to connect a session to the chromecast or an app on the chromecast.
{"type": "PING"} is another common one that should be replied with {"type": "PONG"}.
The different data payloads, in which order they come/should be sent can be seen in this very crude flowchart:
URN‘s that could be re-used.