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03-23-2004, 07:24 AM
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As there have been so many questios in here what the hell is all about the interlaced and progressive state, ... here a little Guide:
(As this thread is locked, please open a new thread in case of questions, thanks )

Whats interlaced?

Interlaced means that you deal with a fieldbased stream shot on VIDEO material, where for example in PAL a fieldrate of 50 fields per second is given by half vertical size! (same logic in case of NTSC means 60 fields per second at half height).
Q: "Well but the movie informations says that my interlaced stream gots its full height and the 25 or 29.97 regular FPS???"
A: ok, thats right because these 50 fields per second (PAL) or 60 fields per second (NTSC) are "weaved" into 25 frames per second (PAL) or 29.97 frames per second (NTSC).


Interlaced1.jpg

So whats the advantage of interlaced streams? You have a smoother realistic movement cause of 50 PAL /60 NTSC uinique fields per second, but on the other hand half vertical resolution on each field!

ALWAYS keep in mind, to keep the full height in an interlaced state, otherwise you would destroy the interlaced architecture. This also means if capturing we everytime keep the full height (480 NTSC or 576 PAL) also if capturing be shure you did set fieldbased- or interlaced-encoding in your choosen capture codec..


What's progressive?

Progressive means that you deal with a framebased stream shot on 35mm FILM material (Hollywood-Blockbuster Movies), where for example in NTSC a framerate of 23.976 fps is given by full vertical size!

That means more details in height but on the other hand not that smooth movement cause of real 23.976fps (NTSC FILM) or 25fps (PAL). Also a reason why movies do appear diff. than Video material.


How to handle/treat interlaced PAL streams? (d2v or AVi)

It depends!
If you got for example a Music concert, means shot on video and therefore real interlaced ... you can deinterlace by choosing the avisynth command

Fielddeinterlace(full=false,blend=false)

... right after the source import Line mpeg2source() or avisource() !!!

But ... you will loose details and the orig. smooth state of the stream is lost. On the other hand, you can reencode using a lower bitrate as interlaced streams do need much more bitrate!

But there do also exist some rare movie DVDs where a PAL telecine is applied, means a Fieldshift! That can be recognised in fast moving scenes where a interlacing "look" does appear. Also in case of PAL Movie capturing via broadcasting stations this can be happen!

So in such a case of an interlaced "looking" MOVIE (not video) like a Hollywoodmovie, in case of PAL you first should try the following in avisynth right after the source import line:

Telecide(Guide=2,post=false)

If still combing does appear .. that could mean:

a) you assumed wrong and your source is NOT a Film but a Video

b) a bad TV station conversation from a 29.97 telecined NTSC Movie to 25 PAL interlaced where no Inverse Telecine was done on the 29.97 to restore the stream back to 23.976! Very bad!
(explained here in german http://home.arcor.de/scharfis_brain/...rlacing/#2.3.3 )

In case a) do the explained Fielddeinterlace() way as described above and in case b) I strongly recommend to encode that stream in mpeg2 interlaced! otherwise you will suffer from blendings which will be seen on Tv!


How to handle/treat interlaced NTSC streams?

Now there are more possibilities how a interlaced NTSC stream is based on:

- a real interlaced NTSC VIDEO stream (concerts, station trailers, etc) means originally shot on VIDEO material
- a telecined NTSC FILM stream where the 23.976 progressive material was pulldowned to 29.97 (common for broadcasting usage, means if you got movie captures)
- a hybrid NTSC 29.97 stream which contains telecined 29.97 NTSC FILM material and beside this also 29.97 real interlaced NTSC VIDEO material.

So how do you can see what you're dealing with?

... in case of DVD sources using DVD2avi:

First: DON'T trust only in DVD2AVIs report on the source in the right statistics window!
If the source is loaded, do move using the slider below to a fast moving scene and watch if "combing" appears, if yes, then you deal with a) a real NTSC VIDEO stream at REAL 29,97 FPS or b) you deal with a telecined NTSC FILM Stream which has been pulldowned usually for broadcasting use.
So in both cases IF YOU SEE combing, don't activate "force film" cause IF combing, your source is NOT progressive and will be 29.97 FPS!

If the source does not come with combing artifacts then you do deal with a truly progressive 23.976 Movie EVEN if DVD2AVI reports "interlaced 29.97"!!!. That means that you have to activate "force film" and a perfect progressive 23.976 d2v prject file will be safed to your HD.

Now if you got a progressive 23.976 d2v file on your HD you can treat it in the known way in Avisynth for example.

IF you got a 29.97 Interlaced d2v file on your hd then you have to watch out if its a telecined one or a really interlaced one.

To handle a telecined 29.97 NTSC stream, just put right after the mpeg2source() import line these commands which do perform a IVTC, means Inverse Telecine:

Telecide()
Decimate()

this restores the telecined 29.976 back to its orig 23.976 progressive state.

If that doesn't work and by this you got a real interlaced 29,97 NTSC VIDEO stream, you can encode that stream in mpeg2 interlaced 29.97fps mode OR using Sharfis_Brain's function to convert that Stream to 23.976 which means less fps and therefore less movieinformation to encode! and by this you will receive more CQ in other words this needs less bitrate!

Here's the function of Sharfis_brain:
(his page where the function is explained: http://home.arcor.de/scharfis_brain/60ito24p.html )

Code:
Mpeg2Source("D:\Your Real Interlaced 29.97 Movie.d2v") 

bob() # or even better "Smoothdeinterlace(doublerate=true, blend=false)"
convert60ito24p(2,0)

.... followed by the resizers, filters and addborders of avisynth



# 
############### the function ############# 
# 
function convert60ito24p (clip video, int mode, int offset) 
{ 
work = assumefieldbased(video) 
out = (mode==2) ? interleave( 
\selectevery( 
\layer(trim(work, 1, 0), 
\layer(work, trim(work, 2, 0), "fast"), 
\"fast"), 5, 0 + offset), 
\selectevery( 
\layer(work, trim(work, 1, 0), "fast"), 5, 3 + offset)) : 
\    (mode==1) ? interleave( 
\selectevery(trim(work, 1, 0), 5, 0 + offset), 
\selectevery(layer(work, trim(work, 1, 0), "fast"), 5, 3 + offset)) : 
\    (mode==0) ? selectevery(work, 5, 1 + offset, 4 + offset) : work 
assumeframebased(out) 
} 
#################################
... in case of NTSC AVI sources like captures:

Also the same thing. If combing does appear in case of captured Hollywood movies you do deal with a telecined NTSC FILM capture, which will be treated by

Avisyource("xxxxxxxx.avi")
Telecide()
Decimate()

If combing does appear in case of REAL interlaced VIDEO roots (concerts, station trailers, documentations etc.), then you can encode that in mpeg2 interlaced at still 29.97 or also here using Sharfis_Brains function as explained above to get to 23.976 fps which are more easy to compress.


I hope this "fast" guide will help

Inc.


A very good source where some explanations above also do come from is the "Exotisches Interlacing" Guide from Sharfis_Brain which can be found here:
http://home.arcor.de/scharfis_brain/...esInterlacing/
Its in german but you can translate it using online-translation tools.


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