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::* MTK NTSC and Twopass - 1st pass::* Unrestricted, Single Pass Encoding, Target Quantizer 6.00 == 1 Pass Quantizer vs Bitrate Mode, vs 2 Pass ==Target quantizer mode uses a fixed quality for each frame. The lower the quantizer the higher the quality. Think of the quantizer as how much data is being thrown out.In target quantizer mode you pick the quality but you don't know what size the file will turn out.In 2-pass VBR mode you pick the file size (file size = bitrate * running time) but you don't know what the quality will be.In general, they are flip sides of the same coin. You use bitrate mode when you want a file of a fixed size. Say, a 700 MB file to fit on one CD. You use quantizer mode when you want a file of known quality.There are a few advantages of VBR bitrate mode. The bitrate caps indicated by the Profile Level are respected. So if you have hardware with bitrate limitations you may want to use that mode, especially when working at high quality levels. And at low quality levels VBR can be a little better at distributing quality. For example, a camera flash going off might cause one frame to be much brighter than the others. Quantizer mode will use more bitrate for that frame because it blindly encodes all frames with the same quality. But in VBR mode the codec knows that you won't really notice if that one frame is encoded at a lower quality. The disadvantage or 2-pass VBR mode is that it takes twice as long to encode.2-pass has a very small advantage in perceived quality (at normal playback speed) when the two methods give the same file size. source: http://www.videohelp.com/forum/archive/xvid-setting-1pass-quantizer-vs-bitrate-mode-vs-2pass-gt-quality-t376841.html