I have a Sony Vaio laptop which is running Ubuntu 10.10. I have switched the sound settings so that the output is to HDMI stereo, but I'm still getting no sound when playing YouTube. I have a Samsung TV. Why isn't there any sound coming from the HDMI connector?
In order to get sound over hdmi in linux, you need to insure the driver your using has support for it. In my case my desktop is running an AMD card that in order for me to get audio I had to switch to the driver from AMD instead of the opensource one. Do you know what video card is in the laptop? If it is INTEL, it should work, if it is AMD I suggest using their driver, same with NVIDIA.