MacOS 10.14 Safari & Amazon Prime

There is something unique about your system as I have no issue

streaming Prime videos with Mojave and Safari 12.

A couple questions:

-Was this an upgrade install over an earlier macOS?

-Do you have Adobe Flash installed?

If you have Adobe Flash installed, you may want to try uninstalling or

otherwise disable it for Amazon as it should not be needed. I do not

have Flash installed and videos play quite well.

I mention the first one since you might be carrying ver some "baggage"

that may be causing the issue.

It may also be worthwhile to download Etrecheck from the App Store

run it and post the results here. There could be some third party app

or plugin that is causing an incompatibility issue.

I'm having trouble with Amazon Prime video as well. I'm using a new Mac mini with Mojave and Safari 12. I can play video, but the audio is out of sync. I am able to play the same videos in Firefox with no issues. And I can play other videos, from other websites, just fine. My old MacBook Air running High Sierra and Safari 12 has no issues with the same videos. It is just something with Amazon and Mojave.

The Amazon help section said to remove and reinstall a Silverlight plugin. I didn't have one, so I installed it. There was no change. Though the plugin doesn't show in the Extensions tab of the Safari Preferences. It does show in Library\Internet Plug-Ins.

FWIW, Safari 12.0.1 in Mojave does not work correctly with Amazon Prime Videos. Firefox and Chrome work fine. Opera may works as well. I have no idea why Amazon tells people to use Silverlight since it's not needed nor is it supported on Macs.

Works here. Check Safari > Preferences > Websites > Auto-Play and make sure Amazon.com is allowed.

If you have an ad blocker try disabling it.

Sorry. I don't read German but there shouldn't be a plugin needed.