WARNING I needed a place to take notes while debugging sound issues after upgrading my desktop from Gutsy to Hardy, so here they are. This is probably a pretty boring read, so continue at your own risk.
Upgraded to Hardy today. Got some indistinct error message at the end, so I made sure and ran aptitude update && aptitude -y full-upgrade && dpkg --configure -a a few times before and after rebooting. Then, when I fired up Firefox (fired up... Firefox... get it...?) and went to youtube I realized I didn't have flash anymore. I aptitude installed flashplugin-nonfree, restarted Firefox, and videos worked. Yay!
Then I went away for a while. When I came back youtube videos had no sound. This is actually a problem that I was having before the upgrade. Not even a reboot helped. I fired up Amarok to see if mp3s still played. Nope, it froze. I googled a bit and found some pulse audio help which led me to believe that maybe I needed to add myself to the pulse audio groups. I did so, tried Amarok again, and the whole system froze. No magic keys or anything could save me. I hit the reset button on my case, and when it came back up, still no youtube sound. I started Amarok and it took forever to start, and then I made sure it was configured to use pulseaudio for its output plugin (I'm using the xine engine), and it didn't freeze, but it didn't play music either. Frustrating. First I had sound problems with Gutsy, and now seemingly worse problems with Hardy. Ubuntu, you've been so good to me in the past. What gives?
Pressing on, I tried changing the output plugin for Amarok and the whole app froze again. I tried watching video with totem, no sound. It froze after a bit too and I had to kill it. This is getting quite scary.
Due to various bugs in the Flash 9 plugin sound output of Flash 9 through the pulseaudio soundserver doesn't work properly. This library adds a clutch to make Flash 9 sound output in pulseaudio possible.
After installing this I shut off my computer completely (I'm in full belt-and-suspenders paranoia mode now), waited a few seconds and then turned it back on.
Taking a more conservative route this time, I started Totem first. No KDE or flash weirdness there. It worked, sound and video played without any problems. Next I tried Amarok with the xine engine output plugin set to autodetect. It worked, no hang. Next, youtube. No sound. Totem and Amarok still worked even after trying flash. I don't know if this result is any different from before, unfortunately. Maybe everything works better as long as you don't do flash first. I don't know.
I'm not sure what to try next. Apparently there might be a newer version of libflashsupport that I could try. This advice is not well explained, but it might be worth a try as well. Overall, I'm getting the impression that this is more the fault of flash than anyone else. Cursed closed-source crap!
I decided to try compiling libflashsupport from source as suggested on the pulse audio wiki. I aptitude removed libflashsupport first. After compiling and installing and restarting firefox there was still no youtube sound. Amarok and Totem were still good though. I rebooted. Still no youtube sound.
And then I saw it. There is a volume control on the little video controls under the youtube video. And it was turned all the way down. Oh. my. gosh. Sure enough, when I turned it up, sound played. How long has that been the problem!?!?!?
I decided to undo what I'd done a bit. I uninstalled libflashsupport as compiled from source and re-installed the ubuntu package. After restarting Firefox youtube and totem both worked, at the same time even. I think I'll leave things like that for now. Don't you love Linux? I do. I really do.