[MPlayer-users] lavc vs. xvid (and improving lavc quality)

[D Richard Felker III]

On Sat, May 29, 2004 at 02:49:16PM -0400, Jason Tackaberry wrote:
> I am primarily interested in high bitrate encoding.  I have ripped most
> of my DVD collection with lavc vqscale=3.  I find this quality isn't
> quite up to my level of expectation, but due to limitations in mplayer
> needed to keep files under 2G.

This is idiotic. You should use 2pass with a specified bitrate.

> My biggest beef with lavc is the blockiness in muddy areas and areas of
> solid colors.  This is an oft observed phenomenon with lavc.  Consider,
> for example, a grey wall in the background that is slightly out of
> focus.  Even at vqscale=2, the blockiness is noticeable and annoying.
> At that quality/bitrate, where areas of high detail are preserved
> excellently, a background of "dancing blocks" is terribly jarring.

Do you perhaps have your monitor brightness turned up insanely high,
and/or messed up gamma "correction"? With proper settings blocks are
not visible even at q=3 or 4.

> I had originally thought this to simply be a limitation of mpeg4 and
> lived with it.  I did try a number of lavc options suggested on this
> list and others, including H263 quantizers, but nothing really improved
> the situation suitably.

Eh? Maybe you mean mpeg quantizers?

> After reading an article on doom9 that stacked up a number of codecs, I

Very bad idea, doom9 is incompetent at codec testing.

> decided to compile xvid into mplayer and give that a try.  I was
> immediately able to see a difference: xvid's artifacting is much more
> pleasant to my eye.

Xvid saves bits by creating mud rather than blocks, which is actually
harded to repair with postprocessing, less accurate, and thus lower
psnr.

> Unfortunately, xvid is also nearly an order of magnitude slower than
> lavc.  I wonder if I've messed something up.  Encoding at 3fps is
> terribly frustrating when lavc gives me 25fps. :)  But I'm willing to
> live with that, as you only encode once, but you watch a lot more.

Hmm, if the difference is this much I expect you're using broken lavc
options, or even a broken version of lavc (perhaps compiled with a
buggy compiler?).

> Wanting to make sure that wishful thinking wasn't interfering with my
> opinion, I crafted a blind comparison between the two.  I picked 5 20-40
> second scenes from my Paycheck DVD and ripped them with each codec.  I
> picked quite high quantizer values, but tried to balance them so that
> the average bitrate of all 5 clips were roughly the same for both
> codecs.  Ultimately I picked vqscale=1.7 for lavc, and fixed_quant=2.5
> for xvid.  (The average bitrate across the 5 clips was about 3100kbit.)

Why don't you just use bitrate settings rather than constant q if you
want to compare?????

Anyway this is interesting if it's correct. At same quant, the two
should give comparable bitrates.

Rich