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Warp

Segmented live media delivery protocol utilizing QUIC streams. See the Warp draft.

Warp works by delivering each audio and video segment as a separate QUIC stream. These streams are assigned a priority such that old video will arrive last and can be dropped. This avoids buffering in many cases, offering the viewer a potentially better experience.

Limitations

Browser Support

This demo currently only works on Chrome for two reasons:

  1. WebTransport support.
  2. Media underflow behavior.

The ability to skip video abuses the fact that Chrome can play audio without video for up to 3 seconds (hardcoded!) when using MSE. It is possible to use something like WebCodecs instead... but that's still Chrome only at the moment.

Streaming

This demo works by reading pre-encoded media and sleeping based on media timestamps. Obviously this is not a live stream; you should plug in your own encoder or source.

The media is encoded on disk as a LL-DASH playlist. There's a crude parser and I haven't used DASH before so don't expect it to work with arbitrary inputs.

QUIC Implementation

This demo uses a fork of quic-go. There are two critical features missing upstream:

  1. WebTransport
  2. Prioritization

Congestion Control

This demo uses a single rendition. A production implementation will want to:

  1. Change the rendition bitrate to match the estimated bitrate.
  2. Switch renditions at segment boundaries based on the estimated bitrate.
  3. or both!

Also, quic-go ships with the default New Reno congestion control. Something like BBRv2 will work much better for live video as it limits RTT growth.

Setup

Requirements

  • Go
  • ffmpeg
  • openssl
  • Chrome Canary

Media

This demo simulates a live stream by reading a file from disk and sleeping based on media timestamps. Obviously you should hook this up to a real live stream to do anything useful.

Download your favorite media file:

wget http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4 -O media/source.mp4

Use ffmpeg to create a LL-DASH playlist. This creates a segment every 2s and MP4 fragment every 10ms.

./media/generate

You can increase the frag_duration (microseconds) to slightly reduce the file size in exchange for higher latency.

TLS

Unfortunately, QUIC mandates TLS and makes local development difficult.

If you have a valid certificate you can use it instead of self-signing. The go binaries take a -tls-cert and -tls-key argument. Skip the remaining steps in this section and use your hostname instead.

Otherwise, we use mkcert to install a self-signed CA:

./generate/cert

With no arguments, the server will generate self-signed cert using this root CA. This certificate is only valid for 2 weeks due to how WebTransport performs certificate fingerprinting.

Server

The Warp server supports WebTransport, pushing media over streams once a connection has been established. A more refined implementation would load content based on the WebTransport URL or some other messaging scheme.

cd server
go run main.go

This can be accessed via WebTransport on https://localhost:4443 by default.

Web Player

The web assets need to be hosted with a HTTPS server. If you're using a self-signed certificate, you may need to ignore the security warning in Chrome (Advanced -> proceed to localhost).

cd player
yarn install
yarn serve

These can be accessed on https://localhost:4444 by default.

If you use a custom domain for the Warp server, make sure to override the server URL with the url query string parameter, e.g. https://localhost:4444/?url=https://warp.demo.