Hi everyone,

Some of you probably remember me. I was involved with trying to get audio/sound implemented in ReactOS a few years ago.

To be honest, my progress was rather poor, I managed to write a few bits of code but never really had a proper understanding of kernel/OS development or CPU/system architectures. Additionally, whilst I could grasp how the multimedia APIs (MME) in NT4 worked, and how they interacted with the drivers (audio device X opens device Y and writes buffered data to it) for Windows 2000 and later, Kernel Streaming was used which partly built on top of the older implementation but added a load of new stuff.

This complicated matters as firstly, KS uses COM (which I still struggle to wrap my head around) in kernel-mode, secondly there were multiple components involved between the application and the hardware (wdmaud.drv -> wdmaud.sys -> ks.sys -> portcls.sys -> driver as far as I remember), and finally I really struggled to find example code and thorough documentation describing how it all worked.

Ultimately I gave up with that and intended to move to another platform to develop multimedia applications. Not much happened with that.

I remember there were complaints from application developers over Kernel Streaming offering poor latency – instead developers would turn to other technologies such as ASIO or DirectSound. So for recent versions of Windows (Vista onwards?) Microsoft implemented a new, user-mode sound system (WASAPI) which again uses COM but is pretty nicely documented, with code samples.

Having done a little reading about this, it renewed my interest. It still uses COM, and KS.SYS is still present (I assume for compatibility?) but as a lot of this is implemented in user-space I suspect it’d be easier to develop/test.

Aside from this, over the past few years I’ve also gained a better understanding of topics I didn’t know much about previously and I feel more confident at being able to write lower-level stuff that works properly. I’ve also developed more of a keen interest in how Windows works.

So basically I’m considering implementing the current Windows audio system in ReactOS. I’d imagine we don’t need to be too concerned about audio drivers themselves (at least, initially) as vendors tend to offer these and it’s not like we need sound immediately post-install!

The only thing I really lack now is knowledge of how to implement COM classes – at least, outside of using Visual Studio… Anyone got recommended reading or example code for this?

Andrew