Bad news discovered during the alpha: Safari on iPhone is not supported by this development 
This development uses the « MediaSource » API, which is not supported by iPhone Safari:
Safari on iPadOS 13 supports it, as does Safari on macOS, so we can hope it will come to iOS in upcoming releases 
iOS users will therefore see this message for now:
No trolling intended, this API has been available on Android since 2014 and on many other browsers for quite some time (I’m saying this even though I’m full Apple 
)
I don’t think it’s a technical blocker, but more of a « competitive » block to prevent competitors from creating custom video players on mobile. Let’s hope that changes!
Edit: My research on Twitter shows a reply from an Apple engineer who works on WebKit and who says that it is indeed a technical limitation; the implementation on macOS and iPadOS is not satisfactory according to them and they want to do better on iOS:
