[MPlayer-users] RFC: docs update for "how to create a high quality DVD rip"

[Jason Tackaberry]

On Sun, 2004-06-06 at 17:48 -0400, D Richard Felker III wrote:
> 3pass mode should NEVER be used, don't even mention that it exists.

The only reason for this I can think of is that VBR audio causes sync
troubles.  You sort of imply that "3-pass is bad" should be common
wisdom, but I don't really know.

> Leaving audio as AC3 is often a very stupid idea, especially if it's
> only stereo or if you want to rip a long movie. You won't hear the
> difference between 96 kbit vorbis and 448 kbit ac3 unless there's lots
> of music.

I have an A/V receiver and do AC3 pass-through.  I assure you that I
will hear the difference between a 96kbit vorbis and a 448bit 5.1 AC3
stream every single time.  And I'll do a blind test to prove it. :)

Now, an AC3 2.0 audio track, yes, I probably won't hear the difference.
But that's 192kbit.  I'm not saving _that_ many bits by compressing that
to vorbis.  Not to make it worth the effort, IMHO.

> Scaling is good, not bad, when used properly. Your attempt to remain
> "as close to the original dvd as possible" is misguided. As long as
> you're using a fixed bitrate, scaling down a bit will lose MUCH less
> quality than the higher mpeg quantizers will lose.

You're assuming that the goal is to have a file size that fits on a CD
or two.  That's not the intent of this encoding guide.  I admit that
wasn't exactly clearly stated and it should be, because when you have a
700MB goal then suddenly things like finding just the right balance
between quantizer and scale is important.

> Your hqdn3d settings are way too light. The defauls seem about
> optimal.

I think it's better to err on the side of caution.  On some rare
occasions, I've seen the default settings for hqdn3d remove some detail
that I'd prefer to be preserved.  Again, when your angle is lowering the
bitrate to achieve a file size goal, then maybe that's a good thing.

The very light hqdn3d settings do make an appreciable difference in
bitrate without losing detail that I can see (or that I care about).  I
might be able to bring those values up a bit, true, but again for my
purposes, I don't want to over do it.

Still, it might be worth mentioning that those parameters can be
adjusted and experimented with until you find the right values for the
given movie.

> If you only care about constant quantizer and/or insane bitrates, I
> guess your guide is ok, but IMO it sucks to switch discs 4 times while
> watching a movie. And what sucks even more is the bad discontinuities

Yeah, that was the point, sorry that it wasn't very clear.  I don't
think 2200kbit is an insane bitrate.  It's definitely quite high, but
insane?  I have a few hundred gig of space and am happy to use that for
high quality video, rather than picking through a library of burned CDs
and getting lesser quality.

To each his own.

> where a bit of audio or video gets lost or duplicated between the
> multiple parts!

That's always so annoying.  Glad I never have to deal with multi-part
movies, or fumbling with CDs.  Everything's on my harddisk, in one
place, viewable with a click or two on my remote. :)

> Because artifacts and higher quantizers are worse than losing a few
> irrelevant (probably noisy anyway) pixels at the image edges.

That assumes that you'll actually see artifacts and higher quantizers if
you don't crop at multiples of 16.  If that's true, then I definitely
accept the explanation.  I guess it'd be straight forward enough to
check that out for myself. :)

> It's a mix or the information-theoretic problem (wasting space
> encoding a whole macroblock for partial data), a mathematical problem
> (poor convergence of fourier series near a discontinuity), and
> probably also motion estimation issues.

Sounds vague, but also reasonable.  Probably getting a better
explanation than that means I'd be getting in way over my head. ;)

> Correct. After deinterlace or pullup you don't have interlaced viceo
> anymore, do you? Nope. So rules for interlaced video don't apply.

That follows my intuition, but then I've made statements based on my
intuition in the past that have ended up being flat wrong.  So better to
be humble and say "I think" all the time ...

... especially when you're lurking on the list. :)

Cheers,
Jason.