Can an interlaced file appear not to be interlaced on the monitor?

[rcavanah]

Hey guys...

So I'm working with some VOB files, and they're from someone's homemade DVD... Not badly-made, but still unpredictable source material.

I'm trying to determine if the source is interlaced. In VLC, on screen, it doesn't appear to be. Not at all. However, I ran it through gspot, and it indicated that it was interlaced (2:3 pulldown). After editing, when I render from Vegas, the output file is very obviously interlaced. Why would this discrepancy occur? I checked VLC to make sure it's not deinterlacing for playback (and I know it's not, because I can view the interlaced output file and all its lines).

I'm rendering with DVD-9 bitrates in mind (2-pass VBR), so the quality shouldn't deteriorate too much at the re-encode, but with the interlacing discrepancy I really can't compare them.. But I need to, before OK'ing the final render. If indeed the source file is interlaced, but it simply doesn't show, do I need to do something to make sure Vegas is interlacing the output properly to look more like the original file? Or, if Gspot is wrong and I should trust my eye that it's not interlaced, should I maybe render progressive and burn it like that?



(another question, out of curiosity... I test some of the renders on the HDMI out to my TV, but this doesn't seem to deinterlace the newly-rendered file... Does deinterlacing occur on the DVD player, or on the TV?)

[manono]

If you don't see interlacing, then it's not interlaced (assuming your player isn't deinterlacing it). It's very possible it was encoded as progressive 23.976fps with 3:2 pulldown applied so that it outputs interlaced 29.97fps. Most players will ignore the pulldown and show only the progressive frames.

But to be sure, check the framerate GSpot reports for pics/sec, frames/sec, and fields/sec. Report what it says here if you can't figure it out. Or post a sample of a VOB section, ten seconds with steady movement.

As for the other question, both the player and the TV are capable of deinterlacing DVD video. This assumes the player is progressive scan and the display is a progressive one.

[themaster1]

You can try to open the vob with virtualdub mod and navigate frame by frame to see if it's interlaced or progressive

Deinterlacing occur on the Tv for regular dvd players, for models with upsclaers i don't know

[rcavanah]

Okeydokey... Gspot shows this for the source:

- Interlaced.
- 3:2 pulldown.
- 23.976 pics/s
- 29.970 frames/s

And this for the output:

- Interlaced.
- Bottom field first.
- 29.970 pics/s AND frames/s

So there's clearly a discrepancy... and I just ran one more test, playing the output footage on my TV (a couple years old, but nonetheless 720p/1080i), and I can still see a few of the interlacing lines, so there's clearly a problem. The original file looks great on it though.

This footage is most likely to be played on a laptop, or at least an upconverting DVD player on an HD display. When I rendered a sample clip progressive, it looked pretty great on the monitor. So now I suppose my question is this: Should I tweak it in Vegas so it renders with proper interlacing (3:2, 23.976pps, 29.970fps), or just render it progressive? I haven't been able to find 3:2-related stuff in Vegas' menus.

[rcavanah]

Bah! Found it.

I had to uncheck "allow pulldown removal" in the main options, and suddenly "29.970 + 2:3 pulldown" appeared in the framerate options in the render configuration. It looks pretty good (as good as the progressive render), so I assume this is what I should go with?

Thanks very much guys, it's a simple answer but I wouldn't have even known to look into this. This board is a huge help.

[rcavanah]

One question though... Should I use 23.970 as the framerate in the file properties? Or just set everything at output?