Embedded Stream videos generate an error in Safari:
"It looks like there’s a problem
A setting in your browser is blocking cookies. Please disable this setting or open in a new window."
The only workaround is to go to Preferences > Privacy and uncheck the Prevent cross-site tracking setting.
More details here:
Requesting this to be fixed in order to allow Stream videos to play in Safari without needing to turn off "Prevent cross-site tracking".