I've been testing Vista (Ultimate RTM) for a little while, specifically with one of our apps under development.

The video side of things is greatly improved (i.e., rendering video to a window or full screen) but...

...Vista's audio leaves a lot to be desired.

Playing back DV AVI files (or a live DV feed) leads to very choppy audio - on the same PC under XP, the audio is perfect.

After digging, I found out why: Vista uses a completely new audio subsystem. DirectSound is now emulated with software and no longers provides direct access to the audio hardware as it does in pre-Vista Windows.

The fundamental problem with this is that any video processing applications that rely on DirectShow will, by default, use a DirectSound-based audio renderer. Such applications have to be rewritten to get around this.

I have done this with our app and can confirm that, when a non-DirectSound renderer is used, the audio problems go away (same audio hardware, different driver model).

Many modern motherboards have integrated audio, such as SigmaTel High Definition Audio Codec. This is available to applications via DirectSound, WaveOut and the new Vista audio layer.

And there seems to be a bug, too. Using DirectSound, multiple applications can use the same piece of audio hardware - the OS mixes the different audio streams. Using the non-DirectSound way with a DirectShow application removes this mixing problem and, instead of just rendering a single audio stream, the apps lock up/misbehave. (Something else to 'program around'.)

Though Microsoft have their reasons for changing the audio layer with Vista (mainly too many badly-written third party audio drivers causing BSODs), doing away with the hardware-accelerated DirectSound capability is, IMHO, a major oversight.

Many existing applications may not perform as well on Vista, creating a bad user experience. Also, many legacy sound cards won't work - the manufacturers must provide new Vista drivers.

My advice - be cautious about switching to Vista if you have apps that use DirectSound for audio (which includes DirectShow-based multimedia apps).

Consider 64-bit XP Pro if you need a boost. Our 32-bit app definitely benefits from running on the 64-bit OS (since it is so DirectShow intensive).