Submitted 1 day ago by VoxAliorum@lemmy.ml to fediverse@lemmy.world
Hey, I am currently trying to understand a bit better what the Activity Pub allows and what it doesn’t as I am preparing a presentation on that topic.
On Lemmy I can join other servers without having to recreate an account. Does that also work for across Activity Pub supporting software? Could I join a PeerTube page and then post there? Could I upload videos? Could I join Mastodon or Pixelfed and post images?
Quick clarification, because I can’t tell from your words if you’re confused about the concept of federation or not 😅
If by “join” other servers you mean use their site as if logged in, or like you have an account there, then that is not federation. That’s single-sign-on (SSO) and is not a feature of the fediverse (Mastodon, Lemmy, Peertube, etc). That would be like the “login with Facebook” or Google buttons around, where by having this account on site A, you can instantly signup on site B without making a new password or anything. That’s not how federation works.
Federation is like email. I can have an email with GMail, you can have one with Proton, and someone else can have Yahoo, and I can send an email to you anyway. It doesn’t mean I can “join” Proton with my GMail account, it doesn’t mean I have.a Yahoo account, it means I don’t need a Yahoo account to communicate with Yahoo users.
But, if by “join” you meant “join a community” as in subscribe to updates from a group on another server, then most other people’s answers apply. I wouldn’t call that “joining a server”, though, because servers host many communities and you’re not joining all of them.
Joining a community works like joining a mailing list. Activity Pub allows accounts on different servers to communicate without an account on their own server, so my account would send a message to your account saying “I’d like to subscribe to this community, send me a message whenever something happens on it”, and then the other server says “okay, will do”, and the after that will periodically send my server messages saying “hey, here’s that update you asked for”. And when I comment, like right now, it’s like an email being sent from my server to yours, and then your server puts it into the history.
This allows my server to present the community from your server to me, without me having account on your server. Without me having to “join” your server, I’d say.
And so I’d say this also answers your broader questions. Since Activity Pub doesn’t allow me to join other servers, it also doesn’t allow me to join other sites.
So a Lemmy post may be compatible with a Mastodon message sent to a group or something, that’s only because the messages Activity Pub sends are similar. But PeerTube is different software with different buttons, and the existence of those buttons on PeerTube doesn’t change anything about what buttons Lemmy has, and I can’t “login” to a PeerTube server with my Lemmy account, so I don’t gain any special abilities outside of what Lemmy can do.
The only way it would be possible is if Lemmy added a feature for uploading videos that sent the same kinds of messages to other servers that PeerTube sends. Then, if they did that, someone on a PeerTube instance could see these messages coming from Lemmy and interpret them on their server as a PeerTube video or something.
But all that Activity Pub allows is exchanging of information between sites. For them to interoperate in a way that makes sense, they need to exchange the same kind of information.
Good response! You were right. I thought that it would work similarly to SSO i.e. your instance works as an identity provider and your content is then generated on the other page, not send there.
Alright, so following the mail metaphor: lemmy is unable to send a video attachment so it can’t allow you to upload videos to peertube; however, activity pub could allow for that.
I think I have to read up on the exact definition of “group”.
With lemmy account you can only join “groups”, so other Lemmy communities, or equivalent piefed or nodebb.
With a Mastodon account you can also join groups (Lemmy etc), but you can also follow single accounts from any mastodon, pixelfed, peertube etc instance.
Why then having a Lemmy account? The interface, how you see the posts, depends on the software. Lemmy is reddit-like, mastodon is twitter-like etc
If you want to upload your video to a peertube instance, then you need an account on that instance
Also, mbin allows you to follow individual users as well as groups.
Like others have said, you can follow accounts from those servers. If they present themselves as group actors, as Lemmy (unlike Mbin for example) doesn't allow following non-group actors.
You can't however just go to their website and log in with your Lemmy account. ActivityPub doesn't have a built-in mechanism for this, but some platforms like Mastodon iirc have a solution and there have been efforts made to standardize something. But there's nothing supported by the Lemmy side of the fediverse yet afaik.
If you want to subscribe to a group actor from Lemmy but can't find them, try searching for the full URL from its home instance. That should tell it to go and fetch the actor. If you want a Lemmy-like experinece but also the ability to follow non-group actors, switch to Mbin. Same applies there, if you can't find an actor on your instance, search for their full URL on the search page and it should fetch them from their home server.
On Lemmy I can join other servers without having to recreate an account.
Not sure what you mean by “join”. You can participate on other Peertube servers, just as you can participate on other Lemmy servers. If you sign up on another server, you will need another account. But currently Lemmy does not support this. PieFed does.
As for Mastodon, The threadiverse (Lemmy + Piefed, etc) is not intended to follow individuals so it does not have that capability. However if a microblog user replies to a threadiverse user, you will be able to see and interact with that as well.
Hope that helps. Happy to hop on a call or something with you to share what I’ve learned for your presentation.
Definitely helps! Regarding the call offer: I might come back to it once I have a pretty good outline for the presentation to double check/clarify the information I’ve found.
In my opinion this is the biggest shortcoming of the ActivityHub ecosystem. That’s not to say it should have been solved by now, since I don’t know how to decentralize authentication safely. And after using it for a while I’m not sure I want a single account.
But it is a challenge facing newcomers and those trying to recruit them. This group of services is already tough to explain sometimes, and telling them it all interconnects just muddies the waters when you have to explain that it’s not the way they expect.
No. For each Mastodon, Lemmy, or Peertube server you want to join, you need a separate account on the server.
Not true. You can follow Peertube from the other systems. You DO NOT need an account on each. Is it easier to use the platform natively? Yes. But you can follow threads on Lemmy from Mastodon and what not.
I think it’s reasonable to assume that when OP asked about “joining” each platform, they wanted to use each platform natively.
On piefed you can join :
- Peertube channel : https://tarte.nuage-libre.fr/topic/peertube/mondelibre and crosspost them.
- in late 2025 : follow mastodon account.
- follow Pixelfed : not supported.
- later in 2026, mobilizon : we can create event post. The base is ready for futur federation with mobilizon : https://codeberg.org/rimu/pyfedi/issues/291
On mbin, you can join :
- peertube channel
- mastodon account
- pixelfed (probably supported but i don't know well mbin)
Lemmy, i got bad result with peertube. Maybe over time they solved it, i haven't tried it. It was possible but you had to manually retrieve the video.
People from mastodon, pixelfed can post on lemmy, mbin, piefed
Peertube on Lemmy was AFAIK recently fixed.
Thank you! @VoxAliorum@lemmy.ml fyi
hendrik@palaver.p3x.de 1 day ago
I think you can follow Peertube channels and write comments but not post videos. And you can't access Mastodon nor Pixelfed.
Lemmy is centered on the concept of ActivityPub groups. While Mastodon etc are about individuals, they don't use that concept and since following accounts isn't implemented in Lemmy, there is no way to properly interact.
Though there are other software projects. MBin combines both. And Piefed wants to get there, eventually. They already hook into a few more things, but Mastodon or Pixelfed accounts currently aren't a thing either.
INeedMana@piefed.zip 1 day ago
Small nitpick. Lemmy communities are present on Mastodon and can be followed and replied to by Mastodon users. One can see a comment written by someone from Mastodon. We only can't follow a Mastodon user or Mastodon tags from Lemmy
gedaliyah@lemmy.world 1 day ago
Also a Mastodon user can follow a Lemmy user.
The replies will federate but not the threads. So for example, the Mastodon user will get notifications about replies to their comments and the Lemmy user will get notifications of the Mastodon user. However, the two users will see the conversion displayed quite differently, especially if there are more than two users in the conversion.
VoxAliorum@lemmy.ml 1 day ago
Is this a real follow or is this just a redirect? It redirects me to my profile.