Quarter pixel Me (qpel)

[macunkie]

I've been using ffmpegX 0.0.9v to convert avi Xvid mencoder.
I notice that a couple of options arre "Use B-frames" and "Quarter pixel Me".

Can someone help me understand why and when these options should be used? Any articles that disscuss these issues?

Thanks,

[Case]

B-frames
Using Bi-directional Predicted Frames is an option to create smaller files. By looking at both the previous and next frame, the current frame is described by comparing to either one, and the comparision that uses the least number of bits is used.

QPEL
Motion Estimation is a way to encode by looking where a block of pixels moves to, from frame to frame. If you would do this very precise, then you could calculate steps of 1/4 of a pixel, thus Quarter Pixel Motion Estimation. Some (most?) standalone DivX-DVD players do not handle this feature.