obs-websocket/docs/docs/partials/introduction.md

obs-websocket 5.1.0 Protocol

Main Table of Contents

• General Intro
  • Design Goals
• Connecting to obs-websocket
  • Connection steps
    • Connection Notes
  • Creating an authentication string
• Message Types (OpCodes)
  • Hello (OpCode 0)
  • Identify (OpCode 1)
  • Identified (OpCode 2)
  • Reidentify (OpCode 3)
  • Event (OpCode 5)
  • Request (OpCode 6)
  • RequestResponse (OpCode 7)
  • RequestBatch (OpCode 8)
  • RequestBatchResponse (OpCode 9)
• Enumerations
• Events
• Requests

General Intro

obs-websocket provides a feature-rich RPC communication protocol, giving access to much of OBS's feature set. This document contains everything you should know in order to make a connection and use obs-websocket's functionality to the fullest.

Design Goals

• Abstraction of identification, events, requests, and batch requests into dedicated message types
• Conformity of request naming using similar terms like Get, Set, Get[x]List, Start[x], Toggle[x]
• Conformity of OBS data field names like sourceName, sourceKind, sourceType, sceneName, sceneItemName
• Error code response system - integer corrosponds to type of error, with optional comment
• Possible support for multiple message encoding options: JSON and MessagePack
• PubSub system - Allow clients to specify which events they do or don't want to receive from OBS
• RPC versioning - Client and server negotiate the latest version of the obs-websocket protocol to communicate with.

Connecting to obs-websocket

Here's info on how to connect to obs-websocket

---

Connection steps

These steps should be followed precisely. Failure to connect to the server as instructed will likely result in your client being treated in an undefined way.

• Initial HTTP request made to the obs-websocket server.

  • The Sec-WebSocket-Protocol header can be used to tell obs-websocket which kind of message encoding to use. By default, obs-websocket uses JSON over text. Available subprotocols:
    • obswebsocket.json - JSON over text frames
    • obswebsocket.msgpack - MsgPack over binary frames

• Once the connection is upgraded, the websocket server will immediately send an OpCode 0 Hello message to the client.

• The client listens for the Hello and responds with an OpCode 1 Identify containing all appropriate session parameters.

  • If there is an authentication field in the messageData object, the server requires authentication, and the steps in Creating an authentication string should be followed.
  • If there is no authentication field, the resulting Identify object sent to the server does not require an authentication string.
  • The client determines if the server's rpcVersion is supported, and if not it provides its closest supported version in Identify.

• The server receives and processes the Identify sent by the client.

  • If authentication is required and the Identify message data does not contain an authentication string, or the string is not correct, the connection is closed with WebSocketCloseCode::AuthenticationFailed
  • If the client has requested an rpcVersion which the server cannot use, the connection is closed with WebSocketCloseCode::UnsupportedRpcVersion. This system allows both the server and client to have seamless backwards compatibility.
  • If any other parameters are malformed (invalid type, etc), the connection is closed with an appropriate close code.

• Once identification is processed on the server, the server responds to the client with an OpCode 2 Identified.

• The client will begin receiving events from obs-websocket and may now make requests to obs-websocket.

• At any time after a client has been identified, it may send an OpCode 3 Reidentify message to update certain allowed session parameters. The server will respond in the same way it does during initial identification.

Connection Notes

• If a binary frame is received when using the obswebsocket.json (default) subprotocol, or a text frame is received while using the obswebsocket.msgpack subprotocol, the connection is closed with WebSocketCloseCode::MessageDecodeError.
• The obs-websocket server listens for any messages containing a request-type field in the first level JSON from unidentified clients. If a message matches, the connection is closed with WebSocketCloseCode::UnsupportedRpcVersion and a warning is logged.
• If a message with a messageType is not recognized to the obs-websocket server, the connection is closed with WebSocketCloseCode::UnknownOpCode.
• At no point may the client send any message other than a single Identify before it has received an Identified. Doing so will result in the connection being closed with WebSocketCloseCode::NotIdentified.

---

Creating an authentication string

obs-websocket uses SHA256 to transmit authentication credentials. The server starts by sending an object in the authentication field of its Hello message data. The client processes the authentication challenge and responds via the authentication string in the Identify message data.

For this guide, we'll be using supersecretpassword as the password.

The authentication object in Hello looks like this (example):

{
    "challenge": "+IxH4CnCiqpX1rM9scsNynZzbOe4KhDeYcTNS3PDaeY=",
    "salt": "lM1GncleQOaCu9lT1yeUZhFYnqhsLLP1G5lAGo3ixaI="
}

To generate the authentication string, follow these steps:

• Concatenate the websocket password with the salt provided by the server (password + salt)
• Generate an SHA256 binary hash of the result and base64 encode it, known as a base64 secret.
• Concatenate the base64 secret with the challenge sent by the server (base64_secret + challenge)
• Generate a binary SHA256 hash of that result and base64 encode it. You now have your authentication string.

For real-world examples of the authentication string creation, refer to the obs-websocket client libraries listed on the README.

Message Types (OpCodes)

The following message types are the low-level message types which may be sent to and from obs-websocket.

Messages sent from the obs-websocket server or client may contain these first-level fields, known as the base object:

{
  "op": number,
  "d": object
}

• op is a WebSocketOpCode OpCode.
• d is an object of the data fields associated with the operation.

---

Hello (OpCode 0)

• Sent from: obs-websocket
• Sent to: Freshly connected websocket client
• Description: First message sent from the server immediately on client connection. Contains authentication information if auth is required. Also contains RPC version for version negotiation.

Data Keys:

{
  "obsWebSocketVersion": string,
  "rpcVersion": number,
  "authentication": object(optional)
}

• rpcVersion is a version number which gets incremented on each breaking change to the obs-websocket protocol. Its usage in this context is to provide the current rpc version that the server would like to use.

Example Messages: Authentication is required

{
  "op": 0,
  "d": {
    "obsWebSocketVersion": "5.1.0",
    "rpcVersion": 1,
    "authentication": {
      "challenge": "+IxH4CnCiqpX1rM9scsNynZzbOe4KhDeYcTNS3PDaeY=",
      "salt": "lM1GncleQOaCu9lT1yeUZhFYnqhsLLP1G5lAGo3ixaI="
    }
  }
}

Authentication is not required

{
  "op": 0,
  "d": {
    "obsWebSocketVersion": "5.1.0",
    "rpcVersion": 1
  }
}

---

Identify (OpCode 1)

• Sent from: Freshly connected websocket client
• Sent to: obs-websocket
• Description: Response to Hello message, should contain authentication string if authentication is required, along with PubSub subscriptions and other session parameters.

Data Keys:

{
  "rpcVersion": number,
  "authentication": string(optional),
  "eventSubscriptions": number(optional) = (EventSubscription::All)
}

• rpcVersion is the version number that the client would like the obs-websocket server to use.
• eventSubscriptions is a bitmask of EventSubscriptions items to subscribe to events and event categories at will. By default, all event categories are subscribed, except for events marked as high volume. High volume events must be explicitly subscribed to.

Example Message:

{
  "op": 1,
  "d": {
    "rpcVersion": 1,
    "authentication": "Dj6cLS+jrNA0HpCArRg0Z/Fc+YHdt2FQfAvgD1mip6Y=",
    "eventSubscriptions": 33
  }
}

---

Identified (OpCode 2)

• Sent from: obs-websocket
• Sent to: Freshly identified client
• Description: The identify request was received and validated, and the connection is now ready for normal operation.

Data Keys:

{
  "negotiatedRpcVersion": number
}

• If rpc version negotiation succeeds, the server determines the RPC version to be used and gives it to the client as negotiatedRpcVersion

Example Message:

{
  "op": 2,
  "d": {
    "negotiatedRpcVersion": 1
  }
}

---

Reidentify (OpCode 3)

• Sent from: Identified client
• Sent to: obs-websocket
• Description: Sent at any time after initial identification to update the provided session parameters.

Data Keys:

{
  "eventSubscriptions": number(optional) = (EventSubscription::All)
}

• Only the listed parameters may be changed after initial identification. To change a parameter not listed, you must reconnect to the obs-websocket server.

---

Event (OpCode 5)

• Sent from: obs-websocket
• Sent to: All subscribed and identified clients
• Description: An event coming from OBS has occured. Eg scene switched, source muted.

Data Keys:

{
  "eventType": string,
  "eventIntent": number,
  "eventData": object(optional)
}

• eventIntent is the original intent required to be subscribed to in order to receive the event.

Example Message:

{
  "op": 5,
  "d": {
    "eventType": "StudioModeStateChanged",
    "eventIntent": 1,
    "eventData": {
      "studioModeEnabled": true
    }
  }
}

---

Request (OpCode 6)

• Sent from: Identified client
• Sent to: obs-websocket
• Description: Client is making a request to obs-websocket. Eg get current scene, create source.

Data Keys:

{
  "requestType": string,
  "requestId": string,
  "requestData": object(optional),

}

Example Message:

{
  "op": 6,
  "d": {
    "requestType": "SetCurrentProgramScene",
    "requestId": "f819dcf0-89cc-11eb-8f0e-382c4ac93b9c",
    "requestData": {
      "sceneName": "Scene 12"
    }
  }
}

---

RequestResponse (OpCode 7)

• Sent from: obs-websocket
• Sent to: Identified client which made the request
• Description: obs-websocket is responding to a request coming from a client.

Data Keys:

{
  "requestType": string,
  "requestId": string,
  "requestStatus": object,
  "responseData": object(optional)
}

• The requestType and requestId are simply mirrors of what was sent by the client.

requestStatus object:

{
  "result": bool,
  "code": number,
  "comment": string(optional)
}

• result is true if the request resulted in RequestStatus::Success. False if otherwise.
• code is a RequestStatus code.
• comment may be provided by the server on errors to offer further details on why a request failed.

Example Messages: Successful Response

{
  "op": 7,
  "d": {
    "requestType": "SetCurrentProgramScene",
    "requestId": "f819dcf0-89cc-11eb-8f0e-382c4ac93b9c",
    "requestStatus": {
      "result": true,
      "code": 100
    }
  }
}

Failure Response

{
  "op": 7,
  "d": {
    "requestType": "SetCurrentProgramScene",
    "requestId": "f819dcf0-89cc-11eb-8f0e-382c4ac93b9c",
    "requestStatus": {
      "result": false,
      "code": 608,
      "comment": "Parameter: sceneName"
    }
  }
}

---

RequestBatch (OpCode 8)

• Sent from: Identified client
• Sent to: obs-websocket
• Description: Client is making a batch of requests for obs-websocket. Requests are processed serially (in order) by the server.

Data Keys:

{
  "requestId": string,
  "haltOnFailure": bool(optional) = false,
  "executionType": number(optional) = RequestBatchExecutionType::SerialRealtime
  "requests": array<object>
}

• When haltOnFailure is true, the processing of requests will be halted on first failure. Returns only the processed requests in RequestBatchResponse.
• Requests in the requests array follow the same structure as the Request payload data format, however requestId is an optional field.

---

RequestBatchResponse (OpCode 9)

• Sent from: obs-websocket
• Sent to: Identified client which made the request
• Description: obs-websocket is responding to a request batch coming from the client.

Data Keys:

{
  "requestId": string,
  "results": array<object>
}