WebM video relay server written in Rust
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webmetro is a simple relay server for broadcasting a WebM stream from one uploader to many downloaders, via HTTP.

The initialization segment is remembered, so that viewers can join mid-stream.

Cluster timestamps are rewritten to be monotonic, so multiple (compatibly-encoded) webm files can be chained together without clients needing to reconnect.


Dependencies & building are handed by Cargo:

cargo build --release

If you're feeling bold, you can let Cargo install it for you:

cargo install


Launch a relay server with the relay subcommand:

webmetro relay localhost:8080

At this point you can open http://localhost:8080/live/main in a web browser. (Or replace "main" with any stream name you like)

Next, a source client will need to POST or PUT a stream to that URL; a static file can be uploaded with the send subcommand:

webmetro send --throttle http://localhost:8080/live/main < file.webm

You can even glue together multiple files, provided they share the same codecs and track order:

cat 1.webm 2.webm 3.webm | webmetro send --throttle http://localhost:8080/live/main

You can use ffmpeg to transcode a non-WebM file or access a media device:

ffmpeg -i file.mp4 -deadline realtime -threads 4 -vb 700k -vcodec libvpx -f webm -live 1 - | webmetro send --throttle http://localhost:8080/live/main

(if the source is itself a live stream, you can leave off the --throttle flag)


  • HTTPS is not supported yet. It really should be. (see "Nginx Proxying" below, though)
  • There aren't any access controls on either the source or viewer roles yet. (see "Nginx Proxying" below, though)
  • The server tries to start a viewer at a cluster containing a keyframe; it is not yet smart enough to ensure that the keyframe belongs to the video stream.
  • The server doesn't parse any metadata, such as tags; the Info segment is stripped out, everything else is blindly passed along.
  • The server drops any source that it feels uses too much buffer space. This is not yet configurable, though sane files probably won't hit the limit. (Essentially, clusters & the initialization segment can't individually be more than 2M)

Nginx Proxying

To get around the current lack of native HTTPS support, you can have nginx terminate the SSL connection; likewise you can have nginx handle access control.

The proxy block will need to include at least the following:

location /webmetro/ {
    # needed to stream PUT request bodies properly
    proxy_http_version 1.1;
    proxy_request_buffering off;
    client_max_body_size 0;

    # alternatively you may wish to bar PUT requests so only local clients can transmit
    # proxy_method GET;

    # proxy to a relay server that's only listening on localhost
    proxy_pass http://localhost:8080/;

This is also useful to simply have the same public port shared by webmetro and a nicely-formatted viewer page.

See Also

  • the Icecast streaming server likewise relays media streams over HTTP, and supports additional non-WebM formats such as Ogg. It does not support clients connecting to a stream before the source, however.


webmetro is licensed under the MIT license; see the LICENSE file.