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hang is a media-specific library built on top of moq-lite for streaming audio and video with WebCodecs compatibility.

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Overview

While moq-lite provides generic pub/sub transport, hang adds media-specific functionality:
  • Catalog: JSON track containing codec info and track metadata
  • Container: Timestamp + codec bitstream or fragmented MP4
  • WebCodecs: Compatible with browser WebCodecs API
Think of hang as similar to HLS/DASH, while moq-lite is like HTTP.

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Installation

Add to your Cargo.toml: 
[dependencies]
hang = "0.15"

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Architecture

┌─────────────────┐
│   Application   │   Your business logic
├─────────────────┤
│      hang       │   Media encoding (this crate)
│                 │   - catalog, container
├─────────────────┤
│    moq-lite     │   Generic pub/sub
└─────────────────┘

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Catalog

The catalog is a special JSON track that describes available media tracks and their codecs.

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Catalog Structure

Each hang broadcast includes a catalog track that contains:
  • Track names and types (audio/video)
  • Codec information
  • Rendition details
  • Live updates as tracks change

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Producing a Catalog

use hang::catalog::Catalog;

// Create a catalog
let mut catalog = Catalog::new();

// Add a video track
catalog.add_track(TrackInfo {
    name: "video".to_string(),
    kind: TrackKind::Video,
    codec: "avc1.42E01E".to_string(),
    width: Some(1920),
    height: Some(1080),
    framerate: Some(30.0),
    bitrate: Some(5_000_000),
});

// Add an audio track
catalog.add_track(TrackInfo {
    name: "audio".to_string(),
    kind: TrackKind::Audio,
    codec: "mp4a.40.2".to_string(),
    sample_rate: Some(48000),
    channels: Some(2),
    bitrate: Some(128_000),
});

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Consuming a Catalog

use hang::catalog::CatalogConsumer;

// Subscribe to catalog updates
let mut catalog_consumer = CatalogConsumer::new(track_consumer);

while let Some(catalog) = catalog_consumer.next().await {
    // Process catalog updates
    for track in catalog.tracks {
        println!("Track: {} ({})", track.name, track.codec);
    }
}
See Catalog on docs.rs

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Container

The container format defines how media frames are encoded within each track.

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Container Formats

hang supports two container formats:

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Legacy Format

A simple format: timestamp followed by codec payload: 
use hang::container::Frame;

// Write a frame with timestamp
let frame = Frame {
    pts: 1000,  // Presentation timestamp in milliseconds
    data: video_data,
};

track.write_frame(frame)?;

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CMAF Format

Fragmented MP4 (moof + mdat pairs): 
use hang::container::CmafFrame;

// Write a CMAF fragment
let fragment = CmafFrame {
    moof: moof_data,  // Movie fragment box
    mdat: mdat_data,  // Media data box
};

track.write_frame(fragment)?;

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Complete Example

use hang::{Catalog, catalog::TrackInfo, catalog::TrackKind};
use moq_lite::{Origin, Broadcast, Track};

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Create MoQ infrastructure
    let origin = Origin::produce();
    let mut broadcast = Broadcast::produce();
    
    // Create catalog
    let mut catalog = Catalog::new();
    catalog.add_track(TrackInfo {
        name: "video".to_string(),
        kind: TrackKind::Video,
        codec: "avc1.42E01E".to_string(),
        width: Some(1920),
        height: Some(1080),
        framerate: Some(30.0),
        bitrate: Some(5_000_000),
    });
    
    // Create catalog track
    let mut catalog_track = broadcast.create_track(Track {
        name: "catalog".to_string(),
        priority: 0,
    })?;
    
    // Publish catalog
    let catalog_json = serde_json::to_vec(&catalog)?;
    catalog_track.write_frame(bytes::Bytes::from(catalog_json))?;
    
    // Create video track
    let mut video_track = broadcast.create_track(Track {
        name: "video".to_string(),
        priority: 1,
    })?;
    
    // Publish broadcast
    origin.publish_broadcast("my-stream", broadcast.consume());
    
    Ok(())
}

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Relationship with moq-mux

For importing existing media formats (fMP4, HLS, etc.) into hang broadcasts, use the moq-mux crate: 
use moq_mux::Mp4Demuxer;

// Import an MP4 file into a hang broadcast
let demuxer = Mp4Demuxer::new(input_file).await?;
let broadcast = demuxer.into_broadcast().await?;

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WebCodecs Compatibility

The hang format is designed to work seamlessly with the browser WebCodecs API: 
// Browser side (TypeScript/JavaScript)
import { Catalog } from '@moq/hang';

// Parse catalog from MoQ track
const catalog = await Catalog.from(track);

// Configure WebCodecs decoder
const decoder = new VideoDecoder({
  output: (frame) => renderFrame(frame),
  error: (e) => console.error(e)
});

decoder.configure({
  codec: catalog.tracks[0].codec,
  codedWidth: catalog.tracks[0].width,
  codedHeight: catalog.tracks[0].height,
});

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Error Handling

All operations return Result<T, hang::Error>: 
match catalog.add_track(track_info) {
    Ok(()) => println!("Track added"),
    Err(e) => eprintln!("Error: {}", e),
}

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Resources

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Next Steps

moq-mux

Import media from fMP4, HLS, and more

moq-cli

Publish media from command line

moq-lite

Learn about the transport layer

TypeScript SDK

Browser-side media handling

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