interlacing

[Statick]

i have a divx file which im converting to dvd using tmpeg mainly.

the source is 23.976 interlace, which i've sped up slightly so that its dvd compliant (i think i went to 29.976 but i cant remember)

anyway, the source is interlaced, which is quite clear if i watch the file on my PC. however, after converting with tmpeg, the resulting DVD shows the same traits watching on TV - slashed horizontal lines across areas of high movement.

but my understanding was that its best to leave interlaced files as interlaced, as i'll be watching them on an interlaced screen.

when i load the file into tmpeg, it tells me its judging the field order, and then the settings come up as 'interlace' and 'bottom field first'

i dont want to go playing with settings without knowing more, as its a 10 hour conversion on my computer, and ive trashed 4 dvd discs already...

[junkmalle]

i have a divx file which im converting to dvd using tmpeg mainly.

the source is 23.976 interlace, which i've sped up slightly so that its dvd compliant (i think i went to 29.976 but i cant remember)

anyway, the source is interlaced, which is quite clear if i watch the file on my PC. however, after converting with tmpeg, the resulting DVD shows the same traits watching on TV - slashed horizontal lines across areas of high movement.

but my understanding was that its best to leave interlaced files as interlaced, as i'll be watching them on an interlaced screen.

when i load the file into tmpeg, it tells me its judging the field order, and then the settings come up as 'interlace' and 'bottom field first'

Normally it is best to leave interlaced sources interlaced -- but there are some very unusual features in your source. First, it's not often you see interlaced Divx files. Second, there is no device that produces or uses 23.976 fps interlaced video. In all likelihood the file has been encoded improperly and you won't be able to convert it as interlaced. If you are lucky it might have been a 25 fps interlaced PAL video that someone slowed down to 23.976 fps thinking it would work that way for NTSC TV (it won't).

What are the frame dimensions? 720x480? That will give a clue about how to handle it.

Some practical considerations: Use a RW disk for testing -- you'll be doing a lot of it. Use TMPGEnc's Source Range option to mark off a small section. No sense in waiting 10 hours for each test!

[manono]

Hi-

I agree with junkmalle (I think). It was almost certainly encoded by an idiot, and you may as well trash it.

I think that the chances of it having been of PAL origin are remote. 23.976fps is progressive film, and it shouldn't be interlaced at that framerate. In order to use it for NTSC DVD, you'd have to make it progressive by deinterlacing, as you can't perform pulldown successfully on an interlaced source (and speeding it up to 29.97fps isn't the answer). It's probably been resized (no longer 480 pixels high), the fields are probably destroyed already, and it can't be deinterlaced successfully anyway. It seems to me that the original encoder probably used Force FILM in DGIndex (DVD2AVI) when he should have either IVTC'd it, or left it at 29.97fps (depending on if it was originally film or video), and my guess is that in addition to being interlaced, it also plays jerky.

[jimmalenko]

however, after converting with tmpeg, the resulting DVD shows the same traits watching on TV - slashed horizontal lines across areas of high movement.

If it's only on areas of the frames with high movement (and not around still objects in the same frames) then it sounds like the field order might be incorrect. Use the Source Range function to just encode a small section, or alternatively, use virtualdub to cut out a 1 min sample (using Direct Stream Copy for both audio and video) for you to play around with until you get the settings as best as you can.

[junkmalle]

I think that the chances of it having been of PAL origin are remote. 23.976fps is progressive film, and it shouldn't be interlaced at that framerate.

I was guessing that somebody thought they could take an interlaced PAL source and convert it to 23.976 NTSC simply by slowing it down -- ie, what you do for progressive PAL sources when you're making a DVD. Of course, as you pointed out, that doesn't work with interlaced material.

It's probably been resized (no longer 480 pixels high), the fields are probably destroyed already, and it can't be deinterlaced successfully anyway.

I was thinking that too -- that's why I asked about the frame size. But it might have simply been cropped, in which case there is some (but not much) hope of fixing it.

If Statick is till watching: post a frame from the video here (recommend you use VirtualDubMod to save a frame). Then we can tell you how to handle it...

[jimmalenko]

If Statick is till watching: post a frame from the video here (recommend you use VirtualDubMod to save a frame). Then we can tell you how to handle it...

https://www.videohelp.com/forum/viewtopic.php?t=271697 might assist with uploading a screenshot.

[manono]

I was guessing that somebody thought they could take an interlaced PAL source and convert it to 23.976 NTSC simply by slowing it down -- ie, what you do for progressive PAL sources when you're making a DVD.

Sure, I wasn't disagreeing with you. I was thinking that if the encoder knew enough to slow it down, and slow the audio as well, that he probably also knew enough to know that it doesn't work with interlaced PAL sources (for DVD anyway), and you'd have to use one of those convoluted scripts like the ones xesdeeni has on his site. For that reason I think the source was originally NTSC. I'd bet dollars to donuts that the original encoder was a total incompetent.

As you say, Statick didn't really give us enough information yet to be sure.

[Statick]

ok guys, thanks for all the help so far

AVIcodec tells me it is 720x480, 23.976 divx 3

so at least its not been re-sized... how would i go about de-interlacing it then?

oh, and i can say fairly confidently that the original source would have been NTSC

[junkmalle]

The easiest thing for you to do is use TMPGEnc's Deinterlace filter. It has about a dozen modes you can try out. But they break down into two basic methods: throw away one field, blend the two fields together. The former results in jagged edges, the latter looks like a double exposure when there are fast motions. Both result in reduced temporal resolution although that's probably the least noticable problem.

Since deinterlacing is always degrades the picture you want to avoid it if possible. What else you might do will depend on exactly how this file became 23.976 fps interlaced.

I recommend you try this: open the file in VirtualDubMod. Add the Deinterlace filter with the "Unfold Fields Side-by-side" option (Video -> Filters... -> Add -> Deinterlace). This will split the two fields apart and place them side by side. You will have a video that's half as tall but twice as wide. Examine the output pane (you can use Options -> Swap input/output panes if you can't see enough of the output pane) if both halves of the image have no comb lines the two fields are intact enough that you might be able to avoid deinterlacing.

Is there any possibility this was originally 29.97 fps and it was slowed down by changing the frame rate with AVIFrate? This would make it play back 20 percent slower than the original but left the actual video intact. If this is the case you can use AVIFrate to change the frame rate back to 29.97 fps. (In case you don't know this: AVI files have a frame rate encoded in the header. This value tell a player how long to display each frame. It's possible to just change that value and have the video play faster or slower.) You'll have to adjust the audio (if any) since the video will now be playing 20 percent faster.

If the two fields are intact, and the video has just been slowed down to 23.976 fps, and you can restore it to 29.97 fps with AVIFrate, it may be possible to inverse telecine back to 23.976 progressive. This can get complicated but you can take a look at the pattern of interlace comb lines to see if it's at all possible. Step through a motion scene one frame at a time in VirtualDubMod (use the left/right arrow keys). If you see a pattern of 3 clear frames followed by 2 interlaced frames you might be able to inverse telecine.

I don't think Divx 3 supported interlaced encoding. That probably means that the chroma (color) channels in the two fields (per frame) have been comingled. This means you will always have slightly blurry colors. In any case, there's nothing you can do about this, the damage has already been done.