Question Re IVTC, DGIndex & NTSC Source

[onesikgypo]

Hi,

From what i gathered - when using an NTSC Source - to determine whther IVTC is needed, when playing it in DGIndex for a few minutes, i was meant to look at the Frame Type, and if its FILM 95% or more then i should force film.

However when i play this clip, the framerate is 29.97 and the Video type just shows as "NTSC" - not film, nor any percentage.

So what does this mean?

Thanks.

[manono]

It means, among other things, that DGIndex is set for the default "Honor Pulldown Flags". That's why it says 29.97. If you were to change the Field Operation to "Forced Film", it'll say 23.976fps.

When it says NTSC/Interlaced with no percentage given it means there's no pure film at all - no progressive 23.976fps with pulldown. Therefore it could be pure interlaced video, hard telecined video (film already telecined and encoded as interlaced), or something else such as field-blended video from a PAL source. Only further inspection of the raw frames and fields will tell you what it is and how to treat it.

Sources needing an IVTC show as you described, but that's only one kind of video that might be NTSC/Interlaced. Make the D2V using "Honor Pulldown Flags" and make a basic AviSynth script with no filtering at all. If it shows the telltale 3 progressive frames and 2 interlaced frames in every 5 frame cycle, then it can be IVTC'd.

If that doesn't help, upload a small 10 second piece of the source somewhere, a piece with motion, and we can have a look.

[onesikgypo]

Hi,

Thanks for replying. After some further research i did find some that said it might be hard telecined (so i then proceeded to continue - i made the d2v file with honouring pulldown option set - i then used decomb in gknot to ivtc with the following options in the avs:

#  IVTC
#Telecide(order=1,guide=1).Decimate()
#  or use
#IVTC(44,11,95)
#GreedyHMA(1,0,4,0,0,0,0,0)
Telecide(order=0)
Decimate(cycle=5)

#  DEINTERLACING (1)
#FieldDeinterlace()
FieldDeinterlace(blend=false)
#TomsMoComp(1,5,1)

However, with the above i just assumed, i didnt look at the frames and such as you mentioned.

Ive uploaded a 20 second clip here: http://rapidshare.com/files/268642011/sample.mpg.html

Also, by basic avisynth script do u mean something like:

LoadPlugin("C:\PROGRA~1\GORDIA~1\DGMPGDec\DGDecode.dll")
LoadPlugin("C:\PROGRA~1\GORDIA~1\AviSynthPlugins\UnDot.dll")

mpeg2source("C:\sample.d2v")

LanczosResize(624,352)

#  DENOISING: choose one combination (or none)
Undot()

ive always mostly dealt with PAL sources, so this has never been an issue for me. I'm not sure how to look at the raw frame fields, but I'd like to be able to figure this all out myself, so if your able to guide me through it all rather then give me an end result, that'd be greatly appreciated.

[manono]

No, I meant:

LoadPlugin("C:\PROGRA~1\GORDIA~1\DGMPGDec\DGDecode.dll")
LoadPlugin("C:\PROGRA~1\GORDIA~1\AviSynthPlugins\U nDot.dll")

mpeg2source("C:\sample.d2v")

I'm getting the sample now...

If you do IVTC, do not also turn on FieldDeinterlace afterwards. Telecide has a conditional deinterlacer built in. It deinterlaces any frames still interlaced after being field matched, although it usually needs to be tweaked for best performance. By adding another deinterlacer afterwards, one that deinterlaces everything, you'll be degrading the already IVTC'd image.

[onesikgypo]

ah right,

well i think i see what you mean now, i looking at the clip it does appear to be 3 progressive frames then 2 interlaced (3 frames that are smooth, then 2 frames that have lines across

So im assuming then that means it is hard telecined and interlaced - which means using the above script with ivtc with decomb was correct?

[manono]

Yep, it's a prime candidate for an IVTC:

# IVTC
#Telecide(order=1,guide=1).Decimate()
# or use
#IVTC(44,11,95)
#GreedyHMA(1,0,4,0,0,0,0,0)
Telecide(order=0)
Decimate(cycle=5)

# DEINTERLACING (1)
#FieldDeinterlace()
#FieldDeinterlace(blend=false)#do not also use this
#TomsMoComp(1,5,1)

[onesikgypo]

Is the Field Deinterlace not required to deinterlace the clip?

Edit: - ok just read more - so i guess since the extra frame is being removed, the frames go back to normal - so then there wont be any interlace left after ivtc has occurred. Question then is, does having the fielddeinterlace as i had it above have any effect at all - i.e during the encoding process would it do anything - or because theres no interlace its equivelant to it being commented?

Also, if this happened to be a case where it werent 3Progressinve 2Interlaced - would this mean that no IVTC was needed at all?

[manono]

Is the Field Deinterlace not required to deinterlace the clip?

If you understood what an IVTC does, you wouldn't ask that question. Read the docs included in the DGMPGDec package. You'll find them in the DGMPGDec folder whereever you installed Gordian Knot. First it field matches the frames and then removes the duplicates. The field matching itself returns all the frames to their progressive origin. Just test that by commenting out (putting a '#' in front) the Decimate line, and then opening the script in VDub(Mod) to have a look.

Also, if this happened to be a case where it werent 3Progressinve 2Interlaced - would this mean that no IVTC was needed at all?

Since you're making AVIs, you have to get rid of the interlacing one way or another. Here you can IVTC. With a poor standards converted DVD (PAL2NTSC or vice-versa) it might mean using an unblender. For pure interlaced video shot with interlaced 29.97fps video cameras, you would apply a real deinterlacer.

Question then is, does having the fielddeinterlace as i had it above have any effect at all l

Read my edited comment about that a couple of posts up. Yes, it has a detrimental effect on the video, and also slows the encoding a little bit.