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== Create H.264 Single File Output ==== Create H.264 Single File Output With FairUse Wizard == == Constant Quantizer versus 2-Pass == When dealing with H.264 video, 2 pass is recommended when targeting an output size. It is also believed to produce a superior quality output stream. Some argue the output is nominally better or the same. The [http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-dvd-mpeg4.html MEncoder documentation] saysThe problem with constant quantizing is that it uses the given quantizer whether the macroblock needs it or not. That is, it might be possible to use a higher quantizer on a macroblock without sacrificing visual quality. Why waste the bits on an unnecessarily low quantizer? Your CPU has as many cycles as there is time, but there is only so many bits on your hard disk. akupenguin, the x264 author:"CRF and 2pass are at the same point on the CBR-to-CPSNR continuum, because they have the same target bitrate distribution. 2pass just ends up slightly closer to that target.)" "benchmarking the existing implementations of crf vs 2pass on several movies. Result: 2pass was better by anywhere from .01 to .12 dB (equivalently, up to 2.5% bitrate at the same psnr). This includes both the effects of ratecontrol (smarter I-frame qp decision) and the fact that direct=auto only really works in 2pass." "x264 keeps track of the "complexity" of each frame, and then determines quantizer from that using the ratecontrol equation (rc_eq) and a quantity called "rate_factor". Assuming an ideal rc_eq, then constant rate_factor would be optimal perceptual RD (not constant quality, but allocating a little more quality in places where it doesn't cost much).ABR and 2pass use the same rc_eq, the primary difference is in how they determine rate_factor. In ABR, we only have statistics about the past frames, so we continually update the estimate of the rate_factor needed to meet the target bitrate. In 2pass, we have all the stats, so we pick the right rate_factor to begin with.To make a 1pass encode that is nearly identical to a 2pass, you'd need to specify rate_factor instead of bitrate or QP. (There will still be some differences: 1pass uses SATD for complexity, 2pass uses 1st pass's bitsize; I-frame quants are selected differently.)" For a full discussion, see [http://forum.doom9.org/archive/index.php/t-151938.html xvid: constant quantizer or 2 pass?] on doom9, where xvid and h.264 are both discussed. Recommendation: For H.264 it is recommended that you use 2-pass as described in the encoding process of this guide.