The situation: You’re trying to watch a Flash movie in Firefox and you can see video just fine, but the audio is stuttering like a broken record, making it impossible to hear the sound. Audio does not stutter in non-Flash applications. You have the latest version of Flash from the Ubuntu repositories.
What’s going on? This appears to be a bug that many Ubuntu/Kubuntu users are experiencing. It looks like it’s a glitch with Flash. Messing around with your sound architecture is unlikely to help matters, so don’t do that.
Solution: There is a fairly simple workaround. Go to Tools > Add-ons. Select “Plugins”. Disable your Flash plugin. Restart Firefox. Then, go back to Add-ons and enable the plugin. Try playing a Flash video again and see if the audio works. Repeat this workaround if the problem occurs again.
In some (but not all) other browsers, this problem can be alleviated by simply restarting the browser.
Comment: If you’ve found this post, I hope the above troubleshooting advice helps. I can’t wait for the day when proprietary software is no longer required to view video on the Web. Flash sucks. The advent of HTML5 will hopefully make Flash problems irrelevant and a thing of the past.