For all users, we'd recommend using Chrome. Overall it is much safer for the playback of Flash on Windows and macOS since it is built into the browser itself, and does not to be installed locally on your machine!
If you are running into issues with video playback or video upload in Safari, you need to re-enable Flash for SnappyTV.
Click on the Safari name within the macOS menu bar (top-left of your screen), and then click on Preferences.
Then click on Security --> Plug-in Settings... to see your current rules for Flash whitelisting.
Select Adobe Flash Player from the left-hand bar. Then select the snappytv.com domain and make sure the setting is set to On.
Click Done, and refresh your tab with SnappyTV. All features should now work properly!