Odd deinterlacing question

[iantri]

Hello,

I want to capture and encode a TV show in Xvid format. The problem is this:

The show is filmed 30p. This is good; no nasty quality-losing deinterlacing. However, certain parts (the credits, and occasionally bits of the show) are 60i. This is bad.

Without going through every episode by hand, how can I deinterlace the 60i parts without affecting the 30p parts?

I thought a motion-based deinterlacer would do it (since there is no motion between the "fields" in the 30p parts), but there is a fair bit of noise since it is an analog TV broadcast and I think it would trip it up a fair bit. Is this what the FieldDeinterlace AviSynth plugin in the Decomb package does? It seems to selectively deinterlaced based on a threshold of combing.

To make matters worse, there are occasionally hybrid 30p/60i bits (e.g. while a TV on the show is displaying another fictitious program, there is a credits squeeze where the credits roll by at 60i in the corner but the person introducing the next program is 30p). Also, when I capture it from VHS the signal seems to shift very slightly (1 or 2 pixels) in between fields and it ends up with minor combing around edges at all times, which I think might confuse a motion-based deinterlacer or FieldDeinterlace.

Any advice?

[lordsmurf]

I have no idea. Good luck.

[iantri]

Trying out FieldDeinterlace(full=false), I seem to get exactly what I want -- progressive frames aren't deinterlaced, but interlaced and progressive/interlaced frames frames are area-based deinterlaced.

I tested it on my first-season DVD though -- as I said before, the VHS tapes I have seem to shift slightly between fields (a few pixels). It doesn't look signifigant, but I don't know if it is enough to trip up the filter..

Is it normal for VHS tapes to exhibit that flaw, or is it just mine? Is there a Vdub or Avisynth filter to correct this?

[FulciLives]

Is it normal for VHS tapes to exhibit that flaw, or is it just mine? Is there a Vdub or Avisynth filter to correct this?

It is not normal for VHS tapes to shift or change field order when you capture them BUT it is something that some people experience.

From what I've read it seems mostly to be related to the quality of the tape and possibly using a different VCR and/or using a Full Frame TBC (such as the DataVideo TBC-1000) might ... stress might ... correct the problem.

Although I've read other people having this problem I've never encountered it myself and from what I've read I'm not sure there is an "easy" fix for it other than maybe a Full Frame TBC.

- John "FulciLives" Coleman

[iantri]

I'm not getting phase shifts (I can see this happening with bad tapes, as you say, but luckily I've never had this problem with my card), I just getting a slight bit of jitter between fields with the progressive image -- even though the image is progressive when I capture it there are very slight combing artifacts (like 1-2 pixels worth) on everything, at all time, like the image is not 100% stable and "shifts" slightly from side to side when output by the VCR. It isn't even visible when watched on a TV, and not really noticable except when freeze-frame, but I just tested it and that (plus the analogue noise) seems to confuse it into thinking that a lot of progressive frames are interlaced.

I guess I'll just have to crank the detection threshold and hope it doens't miss interlaced frames (they are few and far between, anyway.. just the credits in most episodes).