[MEncoder-users] RGB => YV12 conversion

[Vladimir Mosgalin]

Hi RC!

 On 2005.09.25 at 13:54:41 -0700, RC wrote next:

> >  I'm talking about high
> > bitrate (1.5-2 mbit/s) encoding that looks just like dvd where
> > postprocessing only destroys details.
> 
> I use bitrates of around 1000.

Maybe that's where the difference lies. IMHO 1 mbit/s isn't enough for
picture to be good enough, or it will require downscaling, which hurts
quality too. I downscale only to nearest divisible by 16 size -
downscaling by 2-14 pixels isn't noticeable at all.

If you don't downscale and don't use postprocessing, I don't really
understand why you don't see artifacts.

> > Maybe you used wrong options in xvid encoding, like forgot to use
> > b-frames (unlike lavc, they don't suck and decrease bitrate without
> > impact on quality), mpeg quantization or 2-pass encoding? 
> 
> B-frames are even enabled by default, and I use them with lavc as well
> much of the time (fade in/out looks terrible otherwise).  Same for
> mpeg_quant, and 2-pass.

fade in/out looks terrible? Heh, I get opposite results, at least
sometimes. If you've got enough bitrate, p-frames only sequence can
produce nice looking fade in, but b-frames almost always make it worse.
But really, it depends..

When I use lavc, I don't use b-frames, because without them lavc
produces good results. On xvid, you have to use them, they always help a
lot (bitrate-wise). However, on some material they just don't cut (no
matter what kind of encoder you use). This is the case where lavc
(without b-frames) can perform better than xvid (without b-frames).

> > Try again, if you watch without postprocessing, there is a great
> > chance that you'll like it.
> 
> Believe me, I've tried.  I'd really love to find a video codec that
> compresses/looks better than lavc, even if encoding does take 10x
> longer. Unfortunately, every source I've tested (mostly NTSC DVDs) shows
> the opposite.

Out of curiosity, have you tried some of this new stuff, like snow, x264
or something else h264-based? I haven't really, but I've seen a few
really good wmv3 samples. 

They all promise a lot, however their promises mostly lie in land "more
quality at very low/low/middle bitrate". While I need "the least
possible bitrate for encode that my eye can't distinguish from dvd". So
far, xvid + no pp is the champion (though for low and middle bitrate
encodes I prefer lavc + pp)

> > Also, in my opinion xvid is always better for real life video, but it
> > performs worse on animation. Lavc can catch up with xvid here
> > sometimes.
> 
> lavc is absolutely incredible on animation.  *cmp=2 qns=3 2bframes,
> etc., and you can get great quality animation at very, very low
> bitrates. 

I haven't tried qns=3, and turning on b-frames never (at least I don't
remember) helped me on animation when encoding with lavc, but I wouldn't
say that it is that much better than xvid.. It is better in some cases,
but not in the most of them.

-- 

Vladimir