[MPlayer-users] Re: Problem with mencoder

[Oliver Fromme]

D Richard Felker III wrote:
 > On Fri, Aug 15, 2003 at 07:46:30PM +0200, Oliver Fromme wrote:
 > > Please don't remove 3pss encoding.  Without it, it is difficult
 > > (though not impossible) to estimate the bitrate when using VBR
 > > mp3 audio, which I always do.
 > 
 > No it's not. VBR always comes out the same average (withing a +- 10
 > kbit margin) for movie-length encodings.

That's already too much.  For a 100 minutes movie, 10 kbps
difference means about 7 Mbyte in file size.  But I want to
calculate the file size as precisely as possible, so it
will fit on an CD-R and use all the space.

 > So just make a table of what
 > bitrates you get with each VBR setting, and then use those to estimate
 > video bitrate.

Those differ a lot.  The average seems to be around 145 kbps
with my settings, but for some DVDs it goes up to 160 and
beyond, in particular when the movie contains much music
(but not always).  On the other hand, I've also had DVDs
for which the VBR mp3 encoding ended up at 120 kbps.  With
the same mp3lame settings.

 > Or....since you have to encode audio in both passes when you don't
 > have 3pass mode, you could just look at the resulting audio bitrate
 > from the first pass, and then change vbitrate parameter slightly in
 > the second pass to compensate.

Hm, I'm not sure if that would work well with 2pass mode.
It is my understanding that the 2pass mode requires that
the parameters for video encoding are exactly the same in
both passes, otherwise the information from the divx2pass
log file would be inaccurate.

Of course, I could just do an additional pass to encode
the audio and throw it away, and then use the bitrate
information for the normal 2pass mode.  That would work,
and I will probably do that if 3pass support is really
dropped from mencoder.  In that case I would in fact encode
the same audio three times, but I don't care much how long
it takes.  Quality and efficient use of the bits is more
important to me.  :-)

Regards
   Oliver

-- 
Oliver Fromme, secnetix GmbH & Co KG, Oettingenstr. 2, 80538 München
Any opinions expressed in this message may be personal to the author
and may not necessarily reflect the opinions of secnetix in any way.

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