Comment 37 for bug 385344

In my case these symptoms were caused by a sound issue. Specifically I was using a USB webcam with built in microphone. When recording, cheese was fighting the sound system for access to the device. That is why preview was no problem (no sound involved), but the instant I tried to record the framerate dropped to something like one frame every two seconds. The workaround was simply to tell the sound system not to use the microphone built into the USB webcam but to use an external mike. That fixed the problem completely for me.

I reported all this in one of the many other bugs that got marked duplicates of this one. That comment seems to have been ignored. I am not sure that all those duplicates really deserve to be duplicates as others seem to be reporting the problem on laptops and in situations with very different hardware setups to mine. However my experience makes me suspect that while the details probably differ, this is most likely a sound issue in all cases. That would explain why preview is just fine but recording is unusable, since only when recording is sound used.

If you have this problem try playing with your sound recording settings in pulseaudio. For example try plugging in an external microphone and telling pulseaudio to use that as default audio source.