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Originally Posted by DeathTheSheep
---Bitrate Variability---
The bitrate variability feature controls how much your datarate can fluxuate at any given time. That is, if you plan on encoding at 500kbps and set this value to 40, the maximum amount of bitrate given to more complex scenes is 700kbps. In a nutshell, the lower you set this value, the better still/non-complex scenes look, but high-motion/complex scenes will look more shabby and garbled. The higher you set this value, the more equal the overall quality will become: still scenes would look worse than with a low value, and high-motion/complex scenes would look a lot better.
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DTS,
I may have misunderstood two of the x264 parameters (ratetol and qcomp) but I believe qcomp is responsible for deciding how much more high motion scenes are compressed (aka lower bitrate) than static scenes. I think ratetol is an additional constraint on how much you allow qcomp to do its job.
I believe that ratetol is the appropriate parameter to set/modify if you have streaming or hardware playback concerns. However, the low/high motion compensation that you are describing in the above quoted text would, I believe, be more appropriately handled by adjustments to qcomp in conjunction with a sufficiently permissive ratetol.
I am a little confused why ratetol defaults so low. I would think you would want to default it as high as possible, and then adjust qcomp for motion compensation issues.
Anyway, just my perhaps misguided thoughts.