IVTC question

[angelleye]

I recently did a capture and I as I was moving through frames I noticed that it has the patter of 2 interlaced frames and 3 progressive frames as if it had been telecined.

I captured at 29.971 frames per second NTSC. Since I noticed the pattern I went ahead and tried an IVTC with VDubMod. I selected the reconstruct from fields - adaptive from the IVTC section in VDubMod and went ahead and encoded as normal...Divx 5.1 resized and cropped.

The output is a little strange. The beginning of the video seems fine...like the IVTC worked. However a couple minutes into it I notice that there are sections that are still interlaced...but very badly...it doesn't simply look like an interlaced frame. Also...the pattern isn't consistent. In one section there might be 2 interlaced frames...then go about 15 frames with progressive...then have just 1 frame that is interlaced again...then a few more progressive...etc.

Any ideas on what might have gone wrong here? Do i just need to deinterlace or what? I'd like to save the space for a higher bitrate if possible. Any info would be great.

[chilledinsanity]

Sounds like you might have a hybrid DVD, those are annoying. You can check my post (http://forum.doom9.org/showthread.php?s=&threadid=63891) on a similar problem. So far it seems to be a juggle between visual quality and smoothness and how far you want to go in a given direction. Also, what DVD is it?

[angelleye]

actually it's not a DVD. It's a capture off of HBO. Very rarely do I see it happen this way...but now that I've been paying attention it does happen at times.

I capture at 640x480 NTSC HuffyYUV. Almost always the source ends up completely interlaced. It's only on these very few HBO captures that I've noticed the pattern of 2 interlaced and 3 progressive frames per every 5. It's a very distinct pattern...looks exactly like any DVD I've done when I use IVTC in GKnot.

I ended up just deinterlacing the entire thing...it came out fine. However, if I could figure this out for future reference and be able to use higher bitrates instead of deinterlacing that would be awsome.

Any ideas would be great!

[angelleye]

wanted to also mention a couple of other things i had tried....

The first time I tried IVTC in VDubMod I went into the frame rate options and selected 'reconstruct from fields - adaptive'. That's what turned out seeming fine at the beginning but didn't workout through the entire thing.

I then started to think...my capture was 29.971 fps. When I use GKnot to do IVTC with DVDs it always sets the frame rate to 25. Which makes sense to me...it's dropping all the extra frames so the rate is now 25...back to original film speed.

So...I tried this in VDubMod. Under the same frame rate options window where I selected the IVTC method I told it to change the frame rate to 25. That time the audio was completely out of synch...not even close.

So...let's say it is a DVD that I'm encoding and I select to IVTC...do I need to enter anything in the frame rate? Or just leave it at 29.971?