x264 encoding occurs too fast in pass 1

[codemaster]

I'm using MEncoder to encode a DVD to H.264 with 2-pass x264, but I don't understand why the first pass is going much faster than the second pass, I mean, in the first pass, x264 encodes about 45 fames in one second, and in the second pass it encodes 6 frames per second, wich is normal for the preset "slower" that I chose, and it should encode 6 fps in pass 1 as well.

[poisondeathray]

By default, 1st pass uses fast settings with 2pass encoding

If you want to enable slow first pass , use --slow-firstpass . I'm not sure what the syntax is in mencoder

http://mewiki.project357.com/wiki/X264_Settings#slow-firstpass

[codemaster]

@ poisondeathray: true

I found out from MEncoder's manual that, the parameter slow_firstpass

disables the following faster options with pass=1: no_8x8dct me=dia partitions=none ref=1 subq={2 if >2 else unchanged} trellis=0 fast_pskip. These settings significantly improve encoding speed while having little or no impact on the quality of the final pass.
This option is implied with preset=placebo.

But If I don't use slow_firstpass I think the bit allocation decisions will not be as accurate as possible in the second pass, or final pass, is this true ?

Syntax is specified in the same manual.

[poisondeathray]

Makes almost no difference

Compare it yourself. Do encodes with it and without it . IMO it's not worth the speed penalty. I've compared 100's

[jagabo]

Why even bother with bitrate based encoding? Just use a constant quality mode. The file will come out with exactly the right bitrate for the quality you ask for -- in a single pass. Try CRF 18. Bitrate based encoding is only useful when you need a file of a particular size. Like when putting a 2 hour movie on a 700 MB CD.

[codemaster]

@ jagabo: true; I didn't knew about CRF until now