[MEncoder-users] interlaced/non-interlaced

[Andrew Berg]

 On 10/9/2010 12:24 AM, Toerless Eckert wrote:
> On Thu, Oct 07, 2010 at 11:13:20PM -0500, Andrew Berg wrote:
> > Most stations in the US (this includes network, cable and premium
> > channels) broadcast 1080i60, the rest do 720p60. 
>
> Well. My comcast cable has way too many channels but only < 100 of them
> are HD, eg: 1080i or 720p. The rest is all 480i.
I meant as far as HD channels go.
> Which standard ? DVD does support 24p and 30p, right ? And converts
> it to 50/60i...
AFAIK, NTSC DVDs can have only 60i (24p is telecined to 60i) and PAL can
have 50i.
> 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.
> 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. 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.
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.