[MEncoder-users] lavc or xvid

[RC]

On Sun, 26 Aug 2007 11:22:03 -0700
Corey Hickey <bugfood-ml at fatooh.org> wrote:

> > *cmp=2 makes for quite a bit of blockiness, and is usually a bad
> > idea.
> 
> Under what circumstances? I have not observed this, though I admit I 
> haven't done any testing of the *cmp options in a long time. 

Under all I've seen.  The only thing helped by *cmp=2 is animation
(and it helps there a lot).  Live action suffers horribly, getting very
blocky.  If you search the list archives, you'll find dozens of
instances of people asking why their encoded video is so blocky (often
with 7000kbps DVD-video encodes), being told by me or others they
should use cmp=0/3 instead of cmp=2 (unfortunately suggested in the HTML
docs), and it never fails that they respond and say how much better that
looks...

And don't bother to suggesting deblocking...  I have yet to see any
deblocking filter that is strong enough to mask blocking artifacts,
without seriously blurring the rest of the video...  That might not be
noticable with Xvid, which blurs everything when encoding, anyway; but I
care about detail, at least enough to put up with a bit of blockiness.

> A long time  ago, *cmp=2 helped my tests' PSNR significantly and made
> the encodes  look a little better.

It certainly does increase PSNR.  I have a simple fix for
that, though...  I completely ignore PSNR.

> ...and in encodes where the bitrate is somewhat low. qns reduces 
> blockiness around sharp edges, 

I've tried it many times, and have never seen such a benefit on live
action.  Again, animation benefits, but cmp=2 has even more effect,
and isn't nearly as slow as qns.

> I disagree. In my experience, 2 B-frames is optimal. The only place 
> B-frames should hurt quality is in high-motion scenes, and an 
> appropriate vb_strategy will avoid that. On that subject, I should
> note:

B-frames can help a lot at low bitrates, but at high bitrates it
usually does nothing, sometimes hurts, and at best it occasionally helps
but very, very little.  The speed-hit is significant, however.