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Media over QUIC

hang ​

crates.iodocs.rsLicense: MIT

A media library built on top of moq-lite for streaming audio and video.

Overview ​

hang provides media-specific functionality on top of the generic moq-lite transport:

  • Broadcast - Discoverable collection of tracks with catalog
  • Catalog - Metadata describing available tracks, codec info, etc. (updated live)
  • Track - Audio/video streams and other data types
  • Group - Group of pictures (video) or collection of samples (audio)
  • Frame - Timestamp + codec payload pair

Installation ​

Add to your Cargo.toml:

toml
[dependencies]
hang = "0.1"

Supported Codecs ​

hang implements most of the WebCodecs specification.

Video:

  • H.264 (AVC)
  • H.265 (HEVC)
  • VP8
  • VP9
  • AV1

Audio:

  • AAC
  • Opus

Quick Start ​

Publishing Video ​

See rs/hang/examples/video.rs for a complete example of creating a broadcast with a video track, catalog, and publishing frames.

Subscribing to Video ​

See rs/hang/examples/subscribe.rs for a complete example of subscribing to a broadcast, reading the catalog, and consuming video frames.

Catalog ​

The catalog is a special track containing JSON metadata about available tracks:

json
{
  "version": 1,
  "tracks": [
    {
      "name": "video",
      "kind": "video",
      "codec": "avc1.64002a",
      "width": 1920,
      "height": 1080,
      "framerate": 30,
      "bitrate": 5000000
    },
    {
      "name": "audio",
      "kind": "audio",
      "codec": "opus",
      "sampleRate": 48000,
      "channelConfig": "2",
      "bitrate": 128000
    }
  ]
}

The catalog is updated live as tracks are added, removed, or changed.

Frame Container ​

Each frame in hang consists of a timestamp and codec bitstream payload. See the video example for the Frame struct in action.

CMAF Import ​

For importing fMP4/CMAF/HLS files, see the moq-mux crate.

Grouping ​

Groups are aligned with natural boundaries:

Video:

  • Start with keyframe (I-frame)
  • Include dependent frames (P/B-frames)
  • Enable joining at group boundaries

Audio:

  • Collection of audio packets
  • Usually 1 second of audio
  • Independent decoding

See the video example for grouping with OrderedProducer.

Prioritization ​

hang automatically prioritizes:

  1. Keyframes - Highest priority (can't decode without them)
  2. Recent frames - Higher priority than old frames
  3. Audio - Often prioritized over video

This is handled automatically based on frame metadata.

CLI Tool ​

The moq-cli package provides a command-line tool (binary name: moq-cli):

bash
# Install
cargo install moq-cli

# Publish a video file
moq-cli publish video.mp4

# Publish from FFmpeg
ffmpeg -i input.mp4 -f mpegts - | moq-cli publish -

# Custom encoding settings
moq-cli publish --codec h264 --bitrate 2000000 video.mp4

See moq-cli --help for all options, or FFmpeg documentation.

API Reference ​

Full API documentation: docs.rs/hang

Key types:

  • Broadcast - Media broadcast with catalog
  • Catalog - Track metadata
  • VideoConfig / AudioConfig - Track configuration
  • Frame - Timestamp + codec bitstream
  • moq-mux - CMAF/fMP4/HLS import

Protocol Specification ​

See the hang specification for protocol details.

Next Steps ​