[MEncoder-users] interlaced/non-interlaced

[Toerless Eckert]

On Sat, Oct 09, 2010 at 06:41:08AM -0500, Andrew Berg wrote:
> AFAIK, NTSC DVDs can have only 60i (24p is telecined to 60i) and PAL can
> have 50i.

http://en.wikipedia.org/wiki/24p#24p_on_DVD

> > No, i totally do not understand that. Assume i have 25p material and
> > want to broadcat it as 50i. What i do then is that i just split
> > up every frame into even and odd lines and broadcast first the odd
> > lines as one field and then the even lines as the second field. Of course
> > i shuold be able to recombine these two fields to a full frame without any
> > loss.
> No. That kind of interlacing would double the resolution and halve the
> frame rate. To maintain frame rate and resolution, all fields have to
> represent a different point in time. This is done with interpolation.

All fields "should"represent a different point in time, but when
TV stations or DVD players convert 24/25/30p to 50/60i, then this
usually does not happen. 

> > Well, let's just assume original 25p -> 50i -> 25p and 30p -> 60i -> 30p.
> > Those cases should be lossless.
> Not if you maintain a constant resolution.
> > Even 24p -> 60i -> 24p should be lossless.
> I think so, but I'm not 100% sure.
> > Thanks, but why would you use a high CRF == low bitrate for material
> > with heavy artifacting ? SHhouldn't that lower bitrate just aggravate
> > artifacts ?
> The idea is that the original artifacts are going to be more obvious and
> distracting than any introduced by raising the CRF value. You'll have a
> lower bitrate and not notice the additional artifacting.

Hmm.. then the additional artefacting shuold be 'nicer'than the
usual mpeg blocking i know ;-)

> It's also
> important to remember that heavily artifacted material with little
> detail is not nearly as compressible as very clean material, even if it
> has a lot of genuine detail.

Right. Which is why i had always considered to require more bits
in encoding the older the material (old == usually more noisy).

> No encoder is smart enough, nor should it even try, to detect what is
> artifacting and what is genuine detail. That is for a human to decide.
> The encoder will preserve video quality, but it won't know whether it's
> preserving wanted details or nasty blocks.

Yeah, well, but the human (me) wants to outsource all the ongoing work
to the DVR/software and not bother about the encoding for clips 
individually ;-) 

Cheers
    Toerless