Sometimes when I play avi's using a software player on my computer, the player is unable to render sound. The happens when I have foobar open and use KS (all other sound playing seems blocked), but also sometimes happens when foobar is not running.

The author of media player classic, a software player, suggested "If foobars audio renderer really shuts down everything else during its operation then I can imagine it stays stuck and DS cannot create its own renderer anymore."

Is this a known problem with KS? Or might my problem be somewhere else?

This is an intermittent problem, so I'm having problems tracking it down. A simple "stop using KS and see if the problem stops" is not very helpful for a once every few days problem I like KS because it uses less CPU than directsound or waveout, at least according to windows 2000 taskbar.

Stop using KS and see if the problem stops.

That's not very helpful

But does the CPU usage really matter? I mean, you've probably got plenty of idle CPU time, unless you're doing something like seti@home or running encoders in the background. Using this kind of logic, I should run my Pentium M at 1.6 GHz all the time so the % CPU usage is lower :B

Create some script/batch file that 1st shuts down fb2k and then calls mpc.
Assign all video file formats that you play back with mpc to this file and use links to it e.g. on desktop for drag'n'drop. Should do what you need

Firstly, there's this little disclaimer at the bottom of the KS Output dialog window in Foobar2000's Preferences.

Secondly, if you choose to ignore this disclaimer, then the only other factor in the problem is your sound card drivers.

Your sound card probably does not support hardware mixing.

Kernel streaming bypasses the windows software mixer, and as a result any other applications are unable to play sound.

However, if you're having this issue when foobar2000 is closed, it must be a problem with your drivers. You may want to try updating them to the last version or playing with "hardware acceleration" settings in control panel - sounds and audio devices.

If none of this helps, you should stop using kernel streaming.

I use foobar2000 and Media Player Classic at the same time all the time.

It has never given me a problem.