4.5 KiB
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:
- WebTransport support.
- 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:
Congestion Control
This demo uses a single rendition. A production implementation will want to:
- Change the rendition bitrate to match the estimated bitrate.
- Switch renditions at segment boundaries based on the estimated bitrate.
- 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.
ffmpeg -i media/source.mp4 -f dash -use_timeline 0 -r:v 24 -g:v 48 -keyint_min:v 48 -sc_threshold:v 0 -tune zerolatency -streaming 1 -ldash 1 -seg_duration 2 -frag_duration 0.01 -frag_type duration media/playlist.mpd
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 -cert and -key argument. Skip the remaining steps in this section.
Otherwise, use mkcert to install a self-signed CA:
mkcert -install
With no arguments, the server will generate self-signed cert using this root CA.
Server
The Warp server defaults to listening on UDP 4443. It supports HTTP/3 and WebTransport, pushing media over WebTransport 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
Web Player
The web assets need to be hosted with a HTTPS server. If you're using a self-signed certificate, you will need to ignore the security warning in Chrome (Advanced -> proceed to localhost). This can be avoided by adding your certificate to the root CA but I'm too lazy to do that.
cd player
yarn install
yarn serve
These can be accessed on https://127.0.0.1:4444 by default.
Chrome
Now we need to make Chrome accept these certificates, which normally would involve trusting a root CA but this was not working with WebTransport when I last tried.
Instead, we need to run a fresh instance of Chrome, instructing it to allow our self-signed certificate. This command will not work if Chrome is already running, so it's easier to use Chrome Canary instead.
Launch a new instance of Chrome Canary:
/Applications/Google\ Chrome\ Canary.app/Contents/MacOS/Google\ Chrome\ Canary --allow-insecure-localhost --origin-to-force-quic-on=127.0.0.1:4443 https://127.0.0.1:4444