x264 is an open source h.264 encoder. Since r1177 it includes a preset system. The give an easy way to balance quality vs encoding speed, ranging from placebo (highest quality) to ultrafast (lowest quality).
I wanted to get an idea what kind of quality/time gains could be archived with these settings. Usually the first steps of extra quality are barely noticeable in encoding time, while the last bits of quality cost significantly more. To verify this statement and to quantify it, I encoded 2 video sequences at 2 resolutions using all 9 available presets. I used PSNR as metric. I’d be the first to admit that PSNR does not correspond to quality, but it correlates reasonably well.