[MEncoder-users] 3-pass encoding with x264

[Grozdan]

On Wed, Apr 21, 2010 at 4:12 PM, Olivier Rolland
<billl at users.sourceforge.net> wrote:
> On Wed, Apr 21, 2010 at 4:03 PM, Grozdan <neutrino8 at gmail.com> wrote:
>> On Wed, Apr 21, 2010 at 3:54 PM, Olivier Rolland
>> <billl at users.sourceforge.net> wrote:
>>> On Wed, Apr 21, 2010 at 3:45 PM, Grozdan <neutrino8 at gmail.com> wrote:
>>>> On Wed, Apr 21, 2010 at 3:33 PM, Olivier Rolland
>>>> <billl at users.sourceforge.net> wrote:
>>>>> Hi,
>>>>>
>>>>> In 3-pass encoding, should I use
>>>>> pass=1 for the 1st pass, pass=3 for the 2nd pass and pass=3 for the 3rd pass
>>>>> or
>>>>> pass=1 for the 1st pass, pass=3 for the 2nd pass and pass=2 for the 3rd pass ?
>>>>>
>>>>> The man page of mplayer says that I should use the former but mewiki
>>>>> (http://mewiki.project357.com/wiki/X264_Settings#pass) says that I
>>>>> should use the later.
>>>>
>>>> pass=1 for 1st pass
>>>> pass=3 for any subsequent pass if you're doing 3 or more passes
>>>
>>> So mewiki is wrong ? Or does mplayer modify the pass number before
>>> sending it to the codec ?
>>
>> I don't know much about mewiki, but it's always been like that in
>> mencoder. And not just for x264, but also for encoding with lavc
>> codecs (eg, mpeg4, etc)
>
> I've just checked the --help of x264 and it says the same as mewiki:
>
>  -p, --pass <1|2|3>          Enable multipass ratecontrol
>                                  - 1: First pass, creates stats file
>                                  - 2: Last pass, does not overwrite stats file
>                                  - 3: Nth pass, overwrites stats file
>
> I then checked mplayer's code and saw that the pass number is passed
> as is. I then suspect that the man page of mplayer is wrong and that
> what is true for lavc is not true for x264.

Then the encoding guide on mplayer's page must be wrong as well....

Three pass encoding? x264 offers the ability to make an arbitrary
number of consecutive passes. If you specify pass=1 on the first pass,
then use pass=3 on a subsequent pass, the subsequent pass will both
read the statistics from the previous pass, and write its own
statistics. An additional pass following this one will have a very
good base from which to make highly accurate predictions of frame
sizes at a chosen quantizer. In practice, the overall quality gain
from this is usually close to zero, and quite possibly a third pass
will result in slightly worse global PSNR than the pass before it. In
typical usage, three passes help if you get either bad bitrate
prediction or bad looking scene transitions when using only two
passes. This is somewhat likely to happen on extremely short clips.
There are also a few special cases in which three (or more) passes are
handy for advanced users, but for brevity, this guide omits discussing
those special cases.

http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-x264.html

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