MoQ Boy

A "Twitch Plays" style demo where Game Boy Color games run server-side and stream live video + audio to web viewers. Anyone can send inputs — all inputs are applied immediately (anarchy mode). Multiple emulator instances can run simultaneously with different ROMs.

This demo showcases MoQ's key differentiators:

• Prefix-based discovery — game sessions are discovered automatically via announcement prefixes
• Bidirectional communication — viewers send button inputs back to the emulator
• Low-latency video + audio — H.264 video and Opus audio at native Game Boy resolution and framerate
• Multi-viewer interaction — all viewers see which buttons are being pressed in real-time

Running

just demo boy

This starts three components in parallel:

1. Relay — a localhost MoQ relay server
2. Emulator publisher — a Rust binary running a Game Boy Color emulator, encoding video + audio
3. Web viewer — a Vite dev server with a browser UI

The default ROM (Big2Small, a GPLv3 puzzle game) is downloaded automatically on first run.

Custom ROM

just demo boy start path/to/game.gb

Multiple Sessions

Run additional instances in separate terminals with different ROMs:

just demo boy start path/to/other.gb

Each session appears in the grid automatically via MoQ's announcement system.

Controls

Click a session card to expand it, then:

• Arrow keys — D-pad
• Z — A button
• X — B button
• Enter — Start
• Shift — Select
• Escape — collapse the card

On-screen buttons are also available. All buttons highlight when pressed (by you or anyone else).

Reset

• Reset button — any viewer can reset the game
• Auto-reset — the game resets after 5 minutes of inactivity, with a countdown warning

Architecture

Path Prefixes

The emulator and viewer use configurable path prefixes to separate authenticated and anonymous traffic:

Environment	Game Prefix	Viewer Prefix
Localhost	anon/boy/game	anon/boy/viewer
Production	demo/boy/game (authenticated)	anon/boy/viewer (unauthenticated)

Broadcast Hierarchy

{gamePrefix}/
  {name}/                           <- game session broadcast
    catalog.json                    <- video + audio renditions (managed by moq-mux)
    video0.avc3                     <- 160x144 H.264 video at ~60fps
    audio0.opus                     <- Opus audio
    status                          <- JSON state (raw moq-lite track)

{viewerPrefix}/
  {name}/
    {viewerId}/                     <- viewer broadcast
      command                       <- JSON commands (raw moq-lite track)

Discovery

• Viewers discover sessions — subscribe to announcements with the game prefix, filter to single-component suffixes
• Emulator discovers viewers — subscribes to the viewer prefix using origin::Producer::with_root()

Auto-Pause

Emulation and encoding are automatically paused when no viewers are watching. When a viewer connects, emulation resumes immediately with a fresh keyframe.

Video Pipeline

The Rust publisher runs a Game Boy Color emulator (boytacean), grabs the framebuffer each frame, and encodes a single rendition:

Track	Codec	Resolution	Framerate	Method
Video	H.264 (avc3)	160x144	~60fps	RGBA -> YUV -> encode via ffmpeg-next

The web viewer upscales with CSS image-rendering: pixelated for crisp pixel art.

Audio Pipeline

The emulator's APU outputs PCM audio samples which are encoded to Opus via ffmpeg-next and published through moq_mux::import::Opus.

Metadata Tracks

Track	Format	Content
status	Raw JSON	{"buttons": ["up", "a"], "latency": {"abc123": 42}}
command	Raw JSON	{"type": "buttons", "buttons": ["left"]} or {"type": "reset"}

These tracks bypass the hang container format — they're raw UTF-8 JSON bytes written directly to moq_lite groups.

Source Code

• Rust publisher: rs/moq-boy/src/ — main.rs, emulator.rs, video.rs, audio.rs, input.rs
• Web viewer: js/moq-boy/src/ — index.ts (Game class), element.ts (web component), ui/ (SolidJS components)
• Demo app: demo/boy/ — HTML page with <moq-boy> element
• Justfile: demo/boy/justfile