Streampixel Pixel Streaming: Sending Custom Startup Messages to Your Unreal Engine 5 App via URL
- Shrenik Jain
- Oct 15
- 4 min read
Streampixel Pixel Streaming: Sending Custom Startup Messages to Your Unreal Engine 5 App via URL
Introduction
Pixel streaming has made it possible to run Unreal Engine 5 applications in a web browser without any installs, by offloading the heavy rendering to a remote GPU server and streaming the output to users via WebRTC. Streampixel, in particular, is a cloud pixel streaming platform for UE5 that enables high-fidelity 3D apps to run instantly in any browser on any device.
In this tutorial, we will explore how to pass custom startup parameters from the frontend to an Unreal Engine 5 application at launch time using Streampixel's Pixel Streaming platform. By leveraging URL query parameters, you can send a JSON message to the Unreal app without building a custom frontend, allowing you to configure the app's initial state (language, scene, user role, features, etc.) as soon as the session starts.
This approach is ideal for one-time setup or context passing when the stream launches, and it works out-of-the-box with Streampixel.
Why Pass Startup Parameters to Unreal Engine 5?
Pixel Streaming decouples the user's local input from the remote Unreal Engine application. Without a messaging system, events or data from the web frontend (running in the user's browser) are not known to the Unreal app running on the cloud server.
Pixel Streaming normally sends user input (keyboard, mouse, touch) from the browser back to the Unreal application over the network. However, beyond basic input, you often need to pass custom data or configuration to the Unreal app when it starts.
Common Use Cases
Load specific levels or scenes based on the user's selection
Set language or localization for the user's region
Indicate user type (e.g., admin vs viewer) to adjust permissions
Enable or disable features at launch
All this context needs to be sent from the client side (browser) to the UE5 app running on the server right when the session begins.
The Streampixel Solution
Traditionally, accomplishing this might involve building a custom HTML or JavaScript frontend that communicates with Unreal via Pixel Streaming's APIs. But Streampixel provides a simpler solution: you can include a JSON message directly in the Pixel Streaming URL that launches the app.
This means no custom frontend code is required for one-time startup parameters. You simply craft the right URL. When the user clicks the link to start the stream, the parameters in the URL will be sent as a JSON payload to the Unreal application once it starts automatically.
Using URL Parameters to Send a JSON Message at Launch
Streampixel's platform makes it easy to append query parameters to your stream URL, which get interpreted as a JSON message on the Unreal side.
Basic URL Structure
Where:
PROJECT_ID is your Streampixel project's identifier (the part of the share URL before the question mark)
The question mark begins the query string of parameters
fieldname is the key for a JSON field, and value is the data you want to send for that field
Example: Sending Color Name
In this example:
abcd1234 is the project ID
The query part will be delivered to Unreal as a JSON object
{
"color": "red"
}
Multiple Parameters
You can include multiple fields by separating them with an ampersand in the URL query. Multiple parameters are combined into one JSON object. You can add as many key value pairs as needed (URL-encoded if there are special characters).
Pro Tip: URL Generator Tool
Streampixel offers an optional URL Generator tool to help format and encode these URLs. This tool (available at urlgenerator.streampixel.io) lets you input your project ID and desired fields and values, and it will output a properly encoded URL ready to use.
This is handy for ensuring characters like spaces, symbols, or non-ASCII text are encoded correctly in the URL query.
Reading URL Parameters in Unreal Engine (Blueprint Setup)
On the Unreal Engine side, you need to set up your application to receive and handle the JSON message that comes from the URL. You can refer to the video above to learn more about it.
Benefits and Flexibility
Any piece of information that your Unreal application might need right at startup can be embedded in the link. Note that it wont be added to the launch argument, it would be sent once the app is already started.
This capability is especially powerful in:
Cloud deployments and multitenant environments
Scenarios where one Unreal application serves many different users or configurations
Dynamic content delivery without separate builds
Example: A single UE5 project streamed via Streampixel could serve multiple clients by loading different configurations based on the URL parameters (one link loads product demo A in English, another link loads demo B in Spanish, etc.).
Conclusion
Streampixel's Pixel Streaming platform provides a convenient way to send custom messages from the frontend to an Unreal Engine 5 app at launch by simply using URL parameters. This approach allows you to pass configuration data, user context, or commands to your UE5 application without any custom frontend development.
Key Takeaways
Construct a share URL with query parameters to inject a JSON payload
Configure everything from language and levels to user roles and feature flags before the first frame is rendered
Use the built-in Pixel Streaming Input component and Blueprint nodes like Get JSON String Value to parse startup parameters
Apply the parameters in game logic easily
Summary
Passing startup parameters via URL is a powerful yet simple technique to tailor pixel streamed experiences.
It enables Unreal Engine on browser scenarios to be more dynamic and context-aware, all through a single click link. Developers can optimize their UE5 pixel streaming deployments by using this feature to deliver personalized, configurable sessions to end-users, improving the overall experience without adding complexity to the frontend.
By leveraging such features on platforms like Streampixel, you can deliver Unreal Engine 5 content to any device via browser with custom behavior from the outset, truly combining the power of real-time 3D with the reach of the web.
Keywords
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