Comment 9 for bug 910654

It might be the case that gstreamer is simply too slow for this. Are you recording with audio enabled? Try disabling it and let me know what are the results.

The problem with ffmpeg is that default installation on Ubuntu doesn't include x264 or vp8 support. If you want it, you have to build ffmpeg from source. If you do that, by following the guide on Ubuntu forums, you will get the nightly build of ffmpeg and x264 and they tend to differ from one build to another. For example, in current build ffmpeg comes with completely different presets for x264. Also libx264 changed few parameters.

I will add ffmpeg support back in the future (before the Precise release), but it will be 'use at your own risk' kind of a thing.