[MEncoder-users] crf, qp, pass params (was - how do u set H264 video ID?)

[Grozdan]

On Tue, Jun 29, 2010 at 5:59 AM, Goga777 <goga777 at bk.ru> wrote:
>> > =================================================================
>> > mencoder -v -v ?-msglevel all=9
>> > /home/gat/DIESEL/TEST_FP24/PF24_10Seconds.MTS -mc 0 -noskip -fps 30000/1001
>> > -delay -0.222 -oac copy -vf pullup,softskip,harddup,scale=1920:1080 -ofps
>> > 24000/1001 -vid 4113 -ovc x264 -x264encopts
>> > bitrate=24000:qp=5:pass=2:nointerlaced:log=3:frameref=2 -o a.avi
>> > =================================================================
>>
>> Your options are kinda silly. why do you use two different encoding
>> modes together? You use qp=5 with pass=2. Those are two different
>> modes - either choose the one or the other. Also, qp should never be
>> used. Use crf instead or pass=2
>
>
> as far as I understand the crf and bitrate options is not compatible.
> Good discussion about of crf, qp, pass, bitrate you can find in MPlayer list here is
>
> http://lists.mplayerhq.hu/pipermail/mplayer-users/2007-January/065203.html
>
> =======================================================================================
> Here's what _I_ think:
> - crf provides very good quality and allows to make do without 2 pass,
> which is cool.
> However, you can't control how big the encode will end up.

This is "normal" and native to quality-based modes like crf and qp.
You can't know in advance how much bitrate the encoder will allocate
because you allow it to do it for you within the constrains of the
value you give it. Also, it uses a different algo to calculate
compared to multipass modes

> - two pass both allow you to control the target bitrate, and allows to
> make a smarter use of the bits you throw at it. Each now pass somewhat
> improves quality over the previous one.

Somewhat correct. Not every pass will improve the quality. It's been
seen that a 3rd pass in x264 is virtually useless and sometimes even
degraded quality compared to 2-pass. Also, multipass is tricky to find
the right bitrates and you'll have to find it for each content you
want to encode as each content is different (one may require more bits
than the other, so you'll have to calculate somehow each time how much
bitrate to give for the specific content). Some people use crf firs to
get an average bitrate, then use that bitrate in 2-pass mode

> - qp is really meant to be used if you know what you do, if you need
> to us lossless mode, or if you really want to _force_ low quants.

crf=0 is also lossless, so qp is virtually useless for regular users ;)

>
> My ranking (in decreasing order of quality):
> 2-pass>crf>qp

My ranking, crf -> 2-pass -> qp

>
> In terms of speed:
> crf,qp>2-pass.
>
>
> Guillaume
>
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