IVTC, ForceFILM and de-interlace

[apakhira]

Hi, first off, is IVTC and Force FILM the same thing?
I was using SimpleDivX for encoding 2 DivX(yeah i'm a newbie) and with IVTC, the video was perfect. But DGIndex reports the source file 2 be NTSC 29.97 (not FILM) Interlaced. Then why is IVTC working? Also if i use "de-interlace" in SimpleDivX it causes stuttering. Why's that? I thought that was supposed 2 happen 4 IVTCing DVDs that were not FILM. Wierd. Pls solve my problem. And another thing, what does SimpleDivX actually do when i"de-interlace" is used?

Thanx

[manono]

Hi-

is IVTC and Force FILM the same thing?

No. You only Force Film when the movie was encoded Progressive. DGIndex will say Progressive Film when the Preview is run.

If it's not Progressive, then you make the D2V with "Honor Pulldown Flags", and the Preview will say NTSC Interlaced. That tells you how it was encoded, and says nothing about the source. It may be one of 2 things. It may be true interlaced 29.97fps video, in which case neither Force Film nor IVTC will work. In that case, for AVI, you deinterlace.

The other case is the more interesting. In many DVDs, the movie will have been "hard telecined". Film, already telecined to 29.97fps, will have been encoded interlaced 29.97fps. Unlike Progressive Film where 23.976fps is stored on the DVD, when you have hard telecine, 29.97fps is stored on the DVD. In those cases you IVTC. How do you tell the difference between true Interlace and hard telecined Film? The only way is to examine the frames. Interlaced video will have every frame interlaced. Hard telecine will have a unique pattern of 3 progressive frames and 2 interlaced frames in every 5 frame cycle. Evidently yours was of this type. You just deinterlace it, and you get a blurry stuttery mess. On the other hand, if you Force Film or IVTC interlaced video, you wind up with a jerky playing, often interlaced mess. You have to figure out what you have before you can figure out how to treat it.

I don't know anything about SimpleDivX. Sorry.

[apakhira]

Thanx. So cud u pls tell me what IVTC and Force FILM do, individually. I know thias may have been askeda hundred times..but even then

[manono]

Force Film reads the flags in the MPEG-2 stream to remove the duplicate frames (open the D2V in Notepad and note the 0 1 2 3 0 1 2 3 sequence of flags, evidence of progressive encoding with progressive flagging applied afterwards). Hard telecined DVDs lack those progressive flags (open the D2V and note either 0 0 0 0 or 2 2 2 2), and IVTC reassembles the fields into progressive frames, then removing the duplicates. Both will convert 29.97fps DVD output back to the original 23.976fps source. Read these 2 documents for more detail:

http://forum.doom9.org/showthread.php?t=87809
http://www.doom9.org/ivtc-tut.htm

[apakhira]

So, basically, Hard Telecine means sheer waste of DVD space. So now that i make a progressive DivX file, if i want 2 view it on a TV which doesn't have progressive input, would there be any kinda problem. And if i encode my DivX as a Hard-Telecined, any way 2 ignore the RFF and BFF flags while viewing on my pc?

Thanx

[manono]

So you've learned a few things since we last spoke, eh?

So, basically, Hard Telecine means sheer waste of DVD space.

Yes, particularly so when you're backing up a DVD9 to a DVDR, and every bit is valuable.

So now that i make a progressive DivX file, if i want 2 view it on a TV which doesn't have progressive input, would there be any kinda problem.

No, none at all, as long as it's made progressive by IVTCing and not by deinterlacing, just as there are no problems when viewing a progressively encoded DVD on an interlaced TV set.

And if i encode my DivX as a Hard-Telecined, any way 2 ignore the RFF and BFF flags while viewing on my pc?

I don't quite follow, since AVIs aren't flagged the way that DVDs are. AVIs are almost always progressive, so in your case, with that kind of a source, you perform IVTC. I think you saw what happens when you make it progressive by deinterlacing.

There are big problems viewing hard telecined DVDs on a PC, or through an HTPC to an HDTV, or through a flag reading Progressive Scan DVD player to an HDTV. All software players, such as PowerDVD, and most Progressive Scan DVD players are flag readers, and if the DVD isn't flagged as progressive, then they will just deinterlace it. Try and play your DVD on the computer using PowerDVD. Pause it and step through it frame by frame. You'll see that 2 of every 5 frames are blurry/blended. When played full speed, it kind of "strobes", or in your words in the first post, it stutters.

But since you're in India (right?), then I expect that you see quite a few of these lousy DVDs. They'll look fine on an interlaced TV set, but as you mentioned, you waste a lot of bits encoding 29.97fps interlaced, when they could have been encoded 23.976fps progressive, with the flags set to output 29.97fps for NTSC television sets.

[apakhira]

Sorry 4 replying late. So now can u enlighten me on those B-frames ppl talk about. They say something like 1B or 2B encoded packed bitstreams r supported by 2day's DVD players but not more. And i also read DVD players don't support H.263. Does it mean the Quantization matrix "H.263/MPEG2" they're talking of?

[manono]

All DVD/MPEG-4 players will play AVIs encoded with the H.263 and MPEG matrices. It's the other custom matrices that will give some players problems, depending on the chipset used. My previous player with a Sigma Designs chipset would play about anything I threw at it, in terms of matrices. My current player, with a MediaTek chipset is a bit more picky. Those with the ESS chipsets play almost nothing except H.263/MPEG, as far as I know. Yes, those are Quantization Matrices.

I don't feel like explaining B-Frames. Here, read this:

http://www.iis.ee.ic.ac.uk/~frank/surp99/report/kht97/work.html

The I, P, and B-Frame explanation is at the bottom under Interframe Compression. Whether or not your player supports multiple B-Frames and packed bitstream in AVI is dependent on the chipset used (I think).

[apakhira]

Thanks 4 the link. Now, since u know about the "lousy" DVDs that come here in India, could u tell me just how they manage 2 put three movies in 1 DVD? The best part is they look good, every software reports 720x576 resoulution but their bitrate is quite low: 1.5-3 Mbps. How do they manage 2 keep such a high quality? Of course, theyre not as good as the "real" DVDs, but at 1.5Mbps they shu've started pixellating with 720x576.

[manono]

Back again?

Well, you have to understand that the Indian DVDs I've seen have been official releases here in the US. While they often have their problems, what you seem to be describing are bootlegs of what probably weren't very good quality official DVDs to begin with.

I might argue with your description of them looking good at bitrates of between 1500-3000. If they look good to you, perhaps you're watching them on a standard TV set which hides a lot of problems, rather than on a good quality HDTV or computer monitor.

In any event, if they really are 720x576 as you say, the encoder can take steps to make them as good as possible at those low bitrates. He can use a low bitrate matrix. He can use Adaptive Quantization to try and keep the video from blocking and pixelating during complex scenes. Athough I doubt they have hardware encoders with that capability, he can do it in software easily enough if these are burned DVDRs. He can apply filtering in the encoder, such as a Low-Pass or Vertical filter. He can apply spatial or temporal filters before feeding it to the encoder. If he's resizing from the source, he can use a smoothing resizer, such as Bilinear. There are some tricks that encoders use to keep up the quality, but I think that if you know what to look for, you can spot lots of problems at those low bitrates.

[apakhira]

U r always right . Now i noticed that there was a little amount of pixellation, if i viewed it thru my pc. Also, it had been smoothened and looked a little low-res than 720x576. There was another one, a little better, whose bitrate averaged out at 5Mbps. And all were DVD-Rs,that i'm sure of.

But when i convert any of them 2 DivX they lose some of their contrast and brightness. Why is that so? It happens even if encoded at the original resolution.

[manono]

Hi-

But when i convert any of them 2 DivX they lose some of their contrast and brightness.

Yes, I see that mentioned a lot. Although that's not a subject I know a whole lot about, I think it probably has more to do with either the overlay settings of your video card, or the settings in your DivX player. You can usually go into the overlay controls of your video card and adjust the brightness and contrast so that it matches as closely as possible what you see through your DVD player. It's different with different video cards, but you usually right-click the desktop and go Properties->Settings->Advanced. From there look around for a way into the overlay controls. Or you can usually do similar things with the player you like to use to play your AVIs. Most of the good ones have such settings.

[apakhira]

The thing is, i viewed both the dvd and the encoded avi thru the same pc and thru the same software. Of curse i cud use overlay controls, but that wud b a little artificial. So i asked why its happening.

[manono]

Sorry, but I guess I can't help on this one. If you have a standalone DivX player, I'd bet that the DivX wouldn't look any darker than the DVD. Mine don't anyway. For some reason, on the computer they can appear some what darker. I'm sure there's a reason. Maybe someone else can help.

You're only allowed to ask questions to which I know the answer.

[junkmalle]

Computer monitors have very different gamma curves than televisions. Video on a computer usually looks daker and lower in contrast. Because of this, DVD player software often brightens the picture while playing DVDs. But it may not do so with AVI files because it makes the assumption that the AVI has been designed for computer use.

Open both files in VirtualDubMod and compare the pictures there. VirtualDubMod shows the exact contents of the file without any enhancements.

[manono]

Gee, I didn't know that. Thank you junkmalle.

[apakhira]

Yeah thanks junkmalle. U r right-i checked it out.