Why interlace problems?

[jefcoop]

I have a probably basic question:

When I play video from an interlaced camera to an interlaced TV, there is no problem. When I first transfer the video to my computer in AVI format, then use Premiere to compile and encode multiple video segments. Then when I make a DVD and play on the TV, any motion in the scene is accompanied by jagged edges that look horrible. I find I need to delinterlace first before using Premiere (using Main Concept standalong encoder).

My question is if the source and final playback device are in fact interlaced, why does this happen? Do the odd/even (or bottom/top) get reversed somehow? Nowadays I have a progressive DLP, but this happened with my older analog TV as well on playback, so it's not just the DVD player playing back on progressive.

I've found some tutorial on this, but usually it's either so technically involved it's hard to follow, or just says to deinterlace it and be done with it. Any simple explanation?

Thanks-
Jeff

[edDV]

You should not deinterlace. Premiere's Mainconcept defaults should get you a properly intelaced DVD. And the DVD player will produce progressive from that.

What is your source video? Is it DV, TV captures, Film source, other?

I think your problems may be upstream of Premiere.

[junkmalle]

An NTSC video signal consists of 59.94 fields per second. You never see a full frame on TV. By the time one field is displayed the previous field has faded away.

When a computer captures an NTSC signal it combines pairs of fields together to fill up full frames. Unfortunately, there is no global agreement on which field to capture first. Some systems capture the top field first then the bottom, some the other way around.

When displaying the video it's important to know which field to display first because the two pictures can come from different points in time. If you play them in the wrong order you will video that jerks back and forth 30 times a second.

NEVER vertically resize interlaced video unless you know exactly what you ar doing. Doing so will likely mess up the two fields and result in terrible artifacts. Even if you know what you are doing avoid vertical resizing whenever possible because there is no perfect way of doing it.

Be sure any conversion software properly detects the source field order. And make sure it creates it's output with the proper field order for the output device. For example DV AVI is usually bottom field first. DVD MPEG2 is top field first. Don't rely on the software to be able to detect the source field order.

Also be aware that the TV output from many graphics cards doesn't handle interlaced video very well.

[jefcoop]

Nowadays I've switched to DV, but the problem is happening if I capture from my older VHS-C tapes.

The first time I made a DVD from them, the SW I was using captured to MPEG (albeit at not the best quality). The resulting video looked fine.

The next time I did it was with ATI's All-in-Wonder card, which dumped to AVI. I used Window's Movie Maker to extract AVI clips from that, and then loaded those clips into Premiere.

Using Preimere's Export function, I selected a decent quality MPEG, but didn't select any sub options, so they were set to their defaults. That is where the problem showed up.

Last week I did change Premiere's settings on export to deinterlace on one clip, but Encore barfed on that clip when generating the DVD saying something useless like "one of your MPEGs is invalid". Process of elimination was the one I did differently. (An aside- nice as Encore can be, it's error messages are frequently next-to-worthless).

Why, though, if source and playback devices are interlaced, is it a problem in between when taking an intermediate step? I see this on both my progressive DLP/DVD playback mode as well as non-progressive 15-year-old analog TV.

Thanks,
Jeff

[jefcoop]

I was writing my last post when junkmalle posted, so I hadn't read that one yet. I had been selecting Bottom Field First for my deinterlacing.

I guess if you select random clips and change the start point in Premiere, you can run into the start point starting on a top field instead of a bottom field (50/50 chance?).

So the jerkiness I see in faster pans or motion in the video is likely from the fields getting reversed? That is what I was thinking it could be. Is it a matter of the 50/50 chance, or is something just consistently reversing the fields?

Thanks,
Jeff

[BLX]

I have a similar problem. I have an Advermedia PCI capture card and i know standard cable is interlaced, but when i hook my xbox to it with the SVIDEO connection it still is interlaced. I tried turning off the de-interlacing features and then also using them to see what happened...

How do you stop it from interlacing from a "digital" signal ( i know svideo isn't a great signal, but i didn't think it was interlaced)

Any ideas??????

Blayze

[junkmalle]

i know standard cable is interlaced, but when i hook my xbox to it with the SVIDEO connection it still is interlaced.

S-video is interlaced just like composite.

[edDV]

I have a similar problem. I have an Advermedia PCI capture card and i know standard cable is interlaced, but when i hook my xbox to it with the SVIDEO connection it still is interlaced. I tried turning off the de-interlacing features and then also using them to see what happened...

How do you stop it from interlacing from a "digital" signal ( i know svideo isn't a great signal, but i didn't think it was interlaced)

Any ideas??????

Blayze

XBox is outputting in interlace on the video out. If not their support line costs will drag the stock to zero.

[edDV]

jefcoop,

Your VHS-C problem is complex due to multiple steps.
If DV works for Premiere, then it looks like Premiere is OK.

[junkmalle]

I guess if you select random clips and change the start point in Premiere, you can run into the start point starting on a top field instead of a bottom field (50/50 chance?).

I don't know premiere but I doubt it lets you cut on fields rather than frames.

You can also reverse field order by cropping an odd number of scanlines off the top of a frame.