Videoroom: ICE restarts as a subscriber

[remvst]

Hey there,

I'm currently building an application using the videoroom plugin and was looking into ICE restarts. So far I think I got them to work for the publishing side, however I find the subscriber side a bit confusing when reading the docs.

Notice that the same exact steps we just went through (watch request, followed by JSEP offer by the plugin, followed by start request with JSEP answer by the viewer) is what you also use when renegotiations are needed, e.g., for the purpose of ICE restarts.

There is no mention of that watch request in the docs (and I get an error if I fire one), so I assumed it was a join request instead.

So I tried to send the following message:

{
  janus: 'message',
  body: {
    request: 'join',
    ptype: 'subscriber',
    room: 2329283243204937,
    feed: 1611781504646,
    audio: true,
    video: true,
    data: true
  },
  transaction: 'TODO0.08565046641877228',
  apisecret: 'janussecret'
}

which gives me an ack back:

{
  janus: 'ack',
  session_id: 6065274145616990,
  transaction: 'TODO0.08565046641877228'
}

and later on an error event (and also an error in Janus' logs):

{
  janus: 'event',
  session_id: 6065274145616990,
  transaction: 'TODO0.08565046641877228',
  sender: 4863436952761774,
  plugindata: {
    plugin: 'janus.plugin.videoroom',
    data: {
      videoroom: 'event',
      error_code: 425,
      error: 'Already in as a subscriber on this handle'
    }
  }
}

This seems fair but still prevents me from getting a new offer from Janus. Is there another (maybe undocumented) request that needs to be fired in order to perform ICE restarts for subscribers?

[tmatth]

There is an issue in the documentation here, as you point out watch is not a valid videoroom request. I believe the sequence you want is:

• join as subscriber you've already joined, so this step isn't needed
• configure with restart:true
• this responds with configured + the JSEP you need to process and send an answer for with a start request to complete the sequence

Hopefully someone more confident with the semantics here can submit a documentation fix PR :)

[remvst]

There is an issue in the documentation here, as you point out watch is not a valid videoroom request. I believe the sequence you want is:

* ~`join` as subscriber~ you've already joined, so this step isn't needed

* `configure` with `restart:true`

* this responds with `configured` + the JSEP you need to process and send an answer for with a `start` request to complete the sequence

Thank you for the quick reply, will try that and report back ;)

[remvst]

Can confirm I received a new offer with this solution (don't forget restart field in the configure request).

So I think there are two issues in the docs:

• the watch request part should be replaced with a configure request
• the restart field should be mentioned in the configure docs

I'd submit a PR but I'm also not super confident about the exact semantics (and also wouldn't want to take credit from you actually coming up with the solution)

[lminiero]

That's a copy/paste type, since watch is a Streaming plugin request, and that's indeed how you restart subscriptions there (you do a watch+start again). Tristan is right, you use configure with a restart:true in the VideoRoom to ask the plugin to send a new offer that originates an ICE restart. I'll update the docs.