Out of sync audio during video playback can be caused by many different issues.
The first thing you should try is restarting your computer. This should clear things up if your sync issues are caused by a bogged down computer or having your web browser for a long period of time.
Next make sure that your computer and web browser are updated to their latest versions.
If the issue persists, check if you have a sync issue with all of the videos that you play or just particular Storyline Online videos. If the issue is with all videos, the likely culprit is something specific to your local device or audio/video setup. For example, the use of an external speaker or projector introducing a delay in playback, which can usually be corrected by configuring an “Audio Sync,” “Audio Delay,” or “Lip Sync” setting.
If the problem only occurs on some Storyline Videos but not all of them, note that some of the older videos may have a small sync issue of only a couple frames. If you experience a more than a few frames of delay, the issue still could be with your web browser. Assuming it is already updated to its newest version, try switching to a different web browser.
If you still continue to have issues, try switching your “Compatibility Mode” to an older version Windows. You can do this right clicking on the shortcut for your browser and selecting “Properties.” On the settings page that opens, click on the “Compatibility” tab and then select the check box for “Run this program in compatibility mode for:” and use “Windows 7” in the drop down menu and then click “Apply”.