I sent a mail a while back about the issues i was having with Sip Communicator - high CPU usage if PulseAudio was used as default output.
The OS is Debian Squeeze 32-bit. I had the issue on 2 computers consistently.
I tried different settings and i came to one interesting conclusion: The issue is somehow related to the webcam. Or something related in the media code.
Now i used build 2814 to test so if there were changes in the media code might be influencing the outcome.
It happened consistently (~80 % of the cases) only if the default output (in ~/.asoundrc) was set to the pulse plug.
Now if i start a call, the CPU usage sometimes (60% or so) goes up to 100%, but if i press the "Send Video" button, it goes back down to ~20% (toggling that button more doesnt have any effect anymore). Quite interesting given that the same happens regardless if i have the webcam activated or not in the settings. But the CPU usage goes down every time (the call continues without problems or interruption).
There is though another issue that is bugging me still - most of the time (90% or so) the calls have poor quality (the sound stutters/crackles) and if i start pavucontrol the Sip Communicators stream is flickering very fast and i cant interact with it.
It seems that there is are ~3 seconds when the stream flickers fast, then for a fraction of a second it becomes stable then flickers again. When it is stable i can interact with it if i move fast.
Sometimes if i pause/unpause the call the sound quality goes back to normal the audio stream in pavucontrol becomes stable. But this doesnt work every time.
The sound quality too is lower than in older builds (pre-2772), there is sometimes a noise if i blow in the mic, maybe the sound levels are clipped - this did not happen in the older builds, the sound was perfect.
I use (always did) only the PCMU codec for SIP because all our equipments use this (and seemingly it has the lowest CPU usage).