The mediaSession coordinator explanation seems to be incorrect.

[MarkLyck]

Hi.

I've been trying to implement SharePlay (Group Activities) on web using the mediaSession.coordinator feature. But the documentation here seems to be incorrect and I have had no success being able to implement it with the current documentation.

There's very little documentation out there on this feature in Safari. In fact I could only find 2 pieces of documentation and they both have errors.

1. This explainer: https://github.com/WebKit/explainers/tree/main/MediaSessionCoordinator
2. The WWDC from Apple on how to implement it: https://developer.apple.com/videos/play/wwdc2021/10189/ (contains coding errors and the solution didn't work at least for me)

Issues in the explainer:

---

1. mediaSession only exists on navigator

the explainer has examples accessing mediaSession on window or just on the "global" object like these:

window.mediaSession.coordinator.addEventListener('coordinatorstatechange', checkForCoordinatorState);
&
mediaSession.coordinator.state

But those are not valid ways to access the mediaSession in Safari? In Safari you have to do navigator.mediaSession to get the mediaSession.

---

2. There's no such thing as mediaSession.addActionHandler

the function navigator.mediaSession.addActionHandler does not exist on any browser.

I'm not sure if this is just a typo? But the real function is called mediaSession.setActionHandler

---

3. There's no settrack event?

This one I'm not sure about, but as far as I can tell from any of the admittedly extremely lackluster documentation, I have not seen anyone besides this repo mention a settrack event? and if I try to set it up, TypeScript complains it's not a valid event, and so far I have not been able to get it to fire anything.

Please elaborate on this.

TypeScript error:
Argument of type '"settrack"' is not assignable to parameter of type 'MediaSessionAction'

---

4. There's no explanation for getURLForTrackIdentifier ?

The documentation mentions: video.src = getURLForTrackIdentifier(getNextTrackItem()) twice.

But this function isn't explained, and of course it doesn't exist on either window. (window.getURLForTrackIdentifier) is not a thing.

---

It would also be really really appreciated providing an example repository of this feature actually working. Given the severe lack of documentation and that supporting SharePlay on web hasn't exactly been a popular feature to implement yet. It would be so helpful for many developers to have just a single working example to go from.

To back up my frustration with documentation, the only other piece of information I can find on mediaSession.coordinator online is this post on the Apple Developer Forums asking if anyone else got it to work, as of writing no one has responded with a success story.

https://developer.apple.com/forums/thread/699531

🙏 please improve the documentation for this. I'd really like to implement this feature.

[smfr]

@jernoble