Video but no sound; sound but no video (Debian, KDE)

[headisdead]

Distro : Knoppix 3.4 HD install.
Soundcard : SB Live
Graphics: NVidia GeForce2

I have my soundcard working perfectly with every audio program I use (xmms, kaffeine, xine, etc). Also, I have video working fine in every video program i [wish to] use (particularly MPlayer, but also kaffeine, xine, xmms).

Problem is, when I open a video in any of these apps I get absolutely no sound. If I then open an mp3, sound is fine again. This is the case with every codec I've tried (avi, real, mpeg).

Anyone had a similar problem? Is there something I'm doing wrong, maybe a module I'm missing or something?

[variant]

useing an aplication such as aumix/gamix/kmix/amixer or something make sure _all_ the sound levels are turned up to full. also are you useing ALSA or OSS and what soundcad do you have. Which kernel and distro you are useing would also be of assistance. How competant are you with linux? (so i can properly word my reply).

[headisdead]

Thanks variant, although I did begin my post with both distro and soundcard. Knoppix=Debian 3r2. Exact same problem occurs when I boot into either Kernel 2.4 or 2.6. The sound levels are all turned up to full on the mixer.

Otherwise, I'd say I'm fairly linux-competent i.e. a fair few years of experience across several distros. Be as technical as you wish