Doubts about script to convert divx 29.97 to divx 23.97

[Talayero]

Hello,

I'd like to convert a film divx 29.97 I have into a divx 23.97 for some ghost effect I can appreciate in my TVpal dissappears, if possible.

At first I intended to use an IVTC, because I thougt the persone who created the divx had forgotten to select forcefilm or apply ivtc, but I put the film in a bobber, in order to analyze it, and I saw 2 identical frames in a row, followed by 2 identical frames in a row. ¿That means a 2:2 pulldown?

Another thing: I also saw 2 identicals + 2 identicals + 2 identicals that are clear and then 2 identicals + 2 identicals that are combed (or blended I don't know the word), that's to say 6 clear and 4 no clear. But that’s 3 progressive Frames, and 2 Interlaced Frames. So, 3:2 pulldown

I’m confused. How can I interpret that?

My question is: Could I write an avisynth script for virtualdubmod to create a new divx without that disgusting ghost effect?

Before analyzing my divx I had managed to create this script, wrong, because the ghost effect has been replaced by an even worse jagged effect:
LoadPlugin("C:\SmoothDeinterlacer.dll")
AVISource("Q:\my movie.avi")
ConvertToYUY2 (interlaced=true)
SmoothDeinterlace(doublerate=true)
ConvertFPS(50)
SeparateFields()
SelectEvery(4,1,2)
Weave()
ConvertToRGB(interlaced=true)

Could anyone please help me to write the right script? Or is this something impossible and I’d better give up?
I could try with SelectEvery(4,0,3), I’m not sure that’s a goog idea.

May be I’m naïve for believing that if you know the frame structure of an avi (that pattern I described above) it must be a way to recreate it.

Thanks in advance.

[junkmalle]

Your source file has been encoded improperly. Someone took a telecined NTSC movie and encoded with a blend deinterlace filter. You will not be able to extract the original 23.976 fps film frames.

The first of the two blended frames contains one field from the previous frame and one field from the "missing" frame. The second blended frame contains the second field from the missing frame and a field from the following frame. Since they were blended together you can no longer reconstruct the missing frame.

[junkmalle]

That said, in theory it's possible to reconstruct the missing frame by "subtracting" the neighboring fields out of the blended frames. Essentially this would be reversing the blend-fields deinterlace. It wouldn't work perfectly but might be acceptable. I've never heard of any software that can do it though.

[Talayero]

Thank you for answering.

So, if I understood right there's no way to separate these two fields from the missing frame and put it together to recreate that missing frame.

Does that applies to every avi that follows that pattern "2 identical frames followed by 2 identical frames"?

I say that because I have another 29.97 divx with that same structure. Amazing that different people made the same mistake!
In this second divx I can't see a clear pattern of blended not blended, I don't know why, but anyway I think It must be also impossible to be fixed.

Now I'm wondering if that ghost effect I can see is only a result of using the blend deinterlace filter, and I'm curious to know if with another 29,97 divx, that only had the "defect" of not having been through an inverse telecine or force film, I would see it clearly or also with some kind of distorting effect.

Thanks again.

[junkmalle]

Thank you for answering.

So, if I understood right there's no way to separate these two fields from the missing frame and put it together to recreate that missing frame.

Does that applies to every avi that follows that pattern "2 identical frames followed by 2 identical frames"?

I say that because I have another 29.97 divx with that same structure. Amazing that different people made the same mistake!
In this second divx I can't see a clear pattern of blended not blended, I don't know why, but anyway I think It must be also impossible to be fixed.

Now I'm wondering if that ghost effect I can see is only a result of using the blend deinterlace filter, and I'm curious to know if with another 29,97 divx, that only had the "defect" of not having been through an inverse telecine or force film, I would see it clearly or also with some kind of distorting effect.

Thanks again.

Yes, since the frames are blurred you cannot extract the two clear fields needed to reconstruct the the missing film frame.

If you step through the video frame by frame you'll see a pattern of 3 clear frames followed by 2 blurry frames. Since you were using a bob deinterlace to view the fields you were seeing each field stretched out to a full frame.

The ghosting you were seeing probably was a result of the blend deinterlace. It's not unusual for people to do that. Especially if the source was captured with dropped frames, or if the source was edited as video.

[junkmalle]

Talayero, I made some sample images that demonstrate what I think is going on with your divx file:



These are 4x enlarged crops from files that I created. They were enlarged with the nearest neighbor algorithm so you can clearly see each pixel. The original film frames were created with a paint program. They were telecined with Tmpgenc. The telecined video was blend deinterlaced with VirtualDub. The final inverse telecined video (from the blend deinterlaced file) was created with VirtualDub.

The first line consists of consecutive frame from the original 23.976 film frames. You can clearly see the three numbers "1", "2" and "3".

The second line is what happens when the film frames are telecined to 29.97 frames per second. You can see that the second video frame contains a field from the first film frame ("1") and a field from the second film frame ("2"). The third video frame contains the other field from the second film frame ("2") and a field from the third film frame ("3"). This video could be inverse telecined to restore the original film frames. You could take a field from frames 2 and 3 to recreate the original "2".

The third line shows what happens when you use a blend deinterlace. All this really does is blur the pairs of fields together. This shows the ghosting you see when you watch the video.

The last line shows what happens when you inverse telecine the video with the blend deinterlace. Since the source no longer contains clear fields from the telecined video, you get parts of all three frames in the IVTC'd result. You see a mixture of "1", "2" and "3".

[Talayero]

I've just seen your explanation. Amazing. Thanks a lot. Now I understand.

I hope that this blend deinterlace will have some positive effect when used correctly, but here It must have been a mistake, I suppose, because the source was clearly a feature film from the nineties edited in dvd, and then I don't think that kind of sources, if well edited, need to be deinterlaced.

I'm not an expert but probably the blend deinterlace is used to disguise, or to soft the interlacing effect, I don't know.