Purely interlaced source - what should final framerate be?

[magicalpig]

I have a source that is NTSC 29.97fps interlaced. I stepped through each frame and I see that every frame in each series of 5 is interlaced.
Sounds like I've got your standard pure interlaced source here.

Now, if I understand correctly, I shouldn't even consider an inverse telecline operation in this case: duplicate frames were never created i
n order to bring some 24fps source up to 29.97 fps; it was never teleclined to begin with and so every frame in this source is unique.

What needs to be done is just some form of deinterlacing. I plan to use smart deinterlace of Gknot unless someone has a better suggestion.

After deinterlacing, I'm going to have a 29.97fps movie without the combing effect. Great. but isn't that a lot of frames per second? Am I s
upposed to get it down to 23.976fps?


Thanks for taking the time to read this and I appreciate any help you could offer.

[manono]

Hi-

Yes, everything you said was correct. The only thing people could have opinions on would be the choice of deinterlacer. If it's pure interlace, then it has to be kept at 29.97fps. If you take it down to 23.976fps, you'll be cutting out non-duplicate frames, as you said, and it becomes jerky when played. And as you implied, it'll have 25% more frames than a 23.976 movie, and you'll need a larger file size to keep the same quality.

[magicalpig]

Cool! I guess I really have worked out a pretty good understanding of the big telecline/interlace issue. (patting myself on the back)

I'm willing to be adventurous and learn how to use the DeComb filters if it means I may get a better de-interlace. Is there a favorite deinterlacer?

Thanks!:cool:

[jggimi]

Give yourself a second pat on the back -- interlace and telecine are confusing subjects. You deserve it.

I happen to like decomb; one reason is that as an avs filter, it's easy to set up some parameters, open the avs file in vdub, and then check a few seconds of movement, frame by frame, to see what it looks like.

Why? The results depend on the content. So you'll probably want to test several different options before picking the one that looks best to you to encode with.

For example, I've run two decodings recently that were from telecined, but hybrid content, where there was constant switching between interlaced and progressive frames. Even though both were Telecined, one eliminated interlaced frames during Force FILM; for the other, Force FILM didn't work -- it created duplicate frames, so I ran different sets of decomb filters, with different parameters 3 or 4 times before settling on a filter solution. The nice thing was each test only took a minute or two, as I wasn't encoding, just frameserving vdub.

[magicalpig]

jggimi,

I put FieldDeinterlace into my avs file and I'm steping through it in virtual dub. It definitely doesnt look interlaced anymore, but Ican't see any difference between the input video and the output video -- should I?

[jggimi]

No, you won't see a difference in Vdub between those windows if all of your filters are in AviSynth. Those windows are for use with Vdub filters.

[JazzMC]

Hello !

This topic was rather informative .

I have a related question :

I wanted to encode content from a NTSC DVD, the content being interlaced .
Now I though that I had to make the 29.97 --> 23.97 downsize EVERY TIME when having a NTSC DVD .

But : the resulting file WAS jerky ...
So there are some interlaced NTSC DVD's where I have to get down to 23.97 and some where I don't ?

Or can I circumvent 23.97 completely ?

Or can the jerkiness be caused by sometjign else entirely ?

Any suggestions welcome .

Cheers,

Jan .

[jggimi]

So there are some interlaced NTSC DVD's where I have to get down to 23.97 and some where I don't ? Bingo!

Short answer: Interlacing is not the same as Telecine, and has little to do with frame rate.

Films designed to be projected in a theater at 24fps that were transfered to NTSC DVD have 6 extra frames added every second. Videos shot with NTSC video cameras stay at 30fps.

Yes, I know, it's 23.976 and 29.97, but you're looking for the short answer.

Video camera content is often interlaced. There are also many DVDs that are hybrid -- some interlaced, some progressive content, all intermixed.

For more -- much more -- info, do a little searching for the words "Telecine" or "Interlace" and you'll find a great many threads on the subject.

[aleph]

it is implied (i think) from what you all said that in Gknot you manually change the FPS from 29.97 to 23.9 in the box detected from the dvd2avi file (if you ivtc)... is that necessary? i never did that as it isnt in the guides... i just checked "IVTC in avs -> correct Frame Count" before encoding.

thanks

[balbrain]

Hi I was just reading through this thread. Gained a lot of knowledge thanx. I wuz just wondering. To start of how do I step thru every frame to check to see if its a pure interlace? (I am a noob)

--Thanx

--balbrain

[jggimi]

open the file in something that can go back and forth a frame at a time. eg: dvd2avi for vobs, vdub or nandub for avi/avs.

[balbrain]

Thats what I tried. I opened the vobs with DVD2AVI 1.76
When i hit preview(F5) it shows
Film Type - "NTSC"
Frame Type - "Interlaced" (This remains the same throughout the preview. Does that mean every frame is interlaced?)

But when I Move frame by frame using the "<" ad ">" buttons then both Film Type and Frame Type are blank.

Can anyone help me identify the source pertaining to the questions raised in this thread?

Thanx

--balbrain

[jggimi]

First, I always start by sliding into the content somewhere and using the [ button before previewing, to avoid getting mislead by interlaced leaders on the content.

Second, the metadata only appears during a preview. You have to actually look at the frames. :o

Turn off Force FILM, find a scene with motion, and go through it frame by frame. If you see interlaced artifacts through more than 2 out of 5 frames, you have content that needs de-interlacing, and should remain at 29.97. If you see interlaced artifacts in 2 out of 5, you have Telecined film content and can IVTC -- see www.doom9.org/synch.htm for more info.

Force FILM can be used only when the metadata allows it.