This could be caused by a browser plugin with a bug. Hopefully, it gets patched in the next version of Adobe Flash.

I was able to have normal playback with version 11.5 r31. Version 11.5 r502 resulted in stuttering sound and video.

This was only happening to me in Chrome 23.0.1271.64

To fix it just disable all Shockwave plugins in Chrome and then enable and test one at a time. To see a list of plugins type the following in the Chrome address field

chrome://plugins

Please post the version of Shockwave that was causing the problem for you here.