24fps and 30fps issues

[fmctm1sw]

I figured out that a movie I was test recording was converted from 24fps to 30fps. I converted to SVCD a 1 minute hunk of the movie with TMPG and converted from 30 fps to 24 (inverse telecine). It looked great when I burned it to a CD-RW and played it on my DVD player. My question is WHY? Why convert to 30fps in the first place? It looked real good playing at 24fps. Am I missing something?

[tonyp12]

What type of source was it?

If it was a NTSC DVD, it was probably in
23.9 frames all along.

DVD2AVI acts like a DVD player when it finds the 3:2 flag
and add an extra frame(s) (e.g interlaced frames) after every 4 one.

Select "force film", to keep it at 23.9 frames/second.


more about that here:
http://www.vcdhelp.com/forum/viewtopic.php?t=116367&highlight=

[fmctm1sw]

Oh sorry, it was a cap from satellite tv. Some old movie off of AMC....

[snowmoon]

There are several factors that apply.

Most movies originate at 24 ( 23.976 ) and are converted to 30 ( 29.97 ) for diplay on US TV's. This is why it is done this way.

TMPGenc is, for the most part, a progressive encoder. It does not handle telecine materal as well as other encoders. It just does not seem to handle the interlacing as well. Most people think that telecine materal is 20% harder to encoder, but that is untrue. For an encoder that can understand interlacing properly, it's only about a 5% hit ( since the fields don't change their is little or nothing to encoder ).

IVTC allows the encoder to work with progressive frames.

So TMPGenc does better with IVTC'ed materal rather than the original telecined source.

[Nelson37]

Telecining adds 1 new frame every four, by duplicating one field from each of two frames and interlacing them seperately, creating not only 2 out of 5 frames as interlaced but also one Entirely New frame. As it is not a simple duplication there is significant frame-to-frame change which uses valuable bitrate. There are different types of Telecining, but the above is most common.

The point of IVTC is to recover that wasted bitrate by removing the duplicate frame. As a side benefit it removes the interlacing, depending on the nature of the source. The 20% gain is not because of difficulty encoding the interlacing, it's because there is 20% less frames to encode.

You can use the same bitrate and fit 20% more movie on disk OR you can raise the bitrate 20% and get better quality for the same time on disk as before IVTC.

For a DVDrip you can use DVD2AVI to remove the flag but for a capture you have to filter out the extra frames.

[fmctm1sw]

Great reading guys, thanks. I didn't notice if it played any faster or not. And what is that ITVC thing?

[snowmoon]

You can use the same bitrate and fit 20% more movie on disk OR you can raise the bitrate 20% and get better quality for the same time on disk as before IVTC.

Since the 20% extra is just duplication and mpeg-2 is based on field differences the actual quality improvement though IVTC is more like 5% or less for encoders that understand interlacing. Also rember that bitrate is per second, not per frame so raising the bitrate 20% will result in a 20% larger file unless you are talking CQ in TMPGenc.

I will say that IVTC will result in a general improvement in quality for most encodes if done properly and on 100% telecine sources.

[turbodood]

I've always found the forced film method in dvd2avi to be well, imperfect. Firstly when you use it, the video in parts will look choppy. As if frames are missing, just taken out. Secondly, it has the same issue with eventual loss of audio sync you get with other programs. It seems to me anyway vidomi and its IVTC are just about the only way to always maintain audio sync, and keep all frames. Xmpeg allows you to keep 29.97 fps, but still loses sync. Its kind of a shame really, using the ivtc with vidomi requires full-rgb encoding and not YUV, making the encoding take much longer than it would otherwise. Course I could be wrong, these are just my observations.

[adam]

I'm not so convinced Snowman. I don't think I could see a %5 difference, but ntscfilm compared to ntsc looks dramatically better to my eyes. Its not even close. Also this is with numerous encoders, not just TMPGenc.

Even if the added fields are basically the same as the previous one, you are still dividing your bitrate up over more parts. If you have 2500kbits to divide up over one second, you are dividing it up between 30 frames instead of 24, thats a pretty significant margin. Maybe on a dvd the difference isn't as noticable because your bitrate is so much higher, but with svcds you have so few bits per pixel, even with the lower resolution. And with vcds it makes a huge difference since it doesn't support interlacing and you have 30 progressive frames rather than 24 to encode.

I think that was just a typo in Nelson's post, I'm sure he knows what he's talking about. He meant to say that by encoding in ntscfilm you can use the same bitrate and get %20 better quality, or you can get a %20 smaller file at the same relative quality.

[adam]

turbodood perhaps you are using a non-stable version of dvd2avi? Only use 1.76 or if you are feeling daring try the very latest release, but all others in between are highly unstable. Other than that you must be doing something wrong because I can assure you that forced film in dvd2avi IS perfect, and the reason is because what it does is very simple. All it does is disable the pulldown flags, so that the film is sent to the encoder exactly as it is stored, rather than undergoing the telecining process first. So if your film is stored at 23.976fps progressive, like most ntsc dvds are, then that is what you will get in the encoder. But if your film has been hard telecined or is hybrid material than dvd2avi must step in and essentially omit frames to make the output 23.976fps, which is when desync and choppiness occur. Forced film should only be used on a pure film soure, (up to %5 ntsc can be allowed because this is just for the logo and credits,) and if you do so then it will work perfectly every time. However, dvd2avi problems with sync in general and this can occur regardless of whether you use forced film or not. The solution is to set dvd2avi to demux instead of decode, or to demux your audio during ripping. Use a different program such as headache or BeSweet to process your audio and you will have no sync problems.

I have used forced film on every applicable ntsc dvd that I have ever ripped, and have yet to have a single problem and I'm talking about close to 350 dvds.

[Nelson37]

Thanks for the correction, ADAM, I was typing too late at night.

DVD2AVI Forced Film does NOT work for a capture file as this is essentially hard Telecined, as Adam stated. I'm sure he just missed the original posters statement about capping from satellite.

Now if the original feed could be captured, then it could be treated more like a DVD rip! Apparently there are some folks doing this for Satellite.

[fmctm1sw]

Ok, sometimes it takes me a while to catch on
My sat tv source (an old movie off AMC) was telecined from 24fps to 30 fps. Reason being that movies are recorded at 24 fps since the idea is not necessarily watch them on tv. It must be at 30fps to play on my tv though. So, when I inverse telecined (IVTC), to 24 fps and burned to CD-RW and played on my tv, I would never see a change becase my DVD player had to change it back to 30fps to play on my tv. Right? 24fps would work (and look better) on my computer though since the "made up" frames were removed. Right?

[adam]

Wrong. No matter what your intended playback device you still have x number of frames to encode and x amount of bitrate to use. The whole point of doing an IVTC is to encode a lower number of frames and have it play back at the higher, standard framerate.

By encoding in ntscfilm you free up alot of bitrate, %20 more actually. The benefit we are talking about occurs during encoding and thus will increase quality regardless of what you play it back on.

[Nelson37]

Well, he's almost got it. The IVTC's clip will look better on any playback device, they all treat it the same way. Most DVD players and Software players will re-do the Telecine back to 30fps, some will require the pulldown flag to be added, some won't, so adding the flag all the time is the best procedure.

As Adam stated, the gain comes from not encoding the "extra" frames, it is not necessary as they will be recreated in hardware.

[Treebeard]

Am I Correct? Need Verification;

1) If forced film is used then it will tell TMGENC to encode at 23.97 fps and therefore you should select (S)VCDfilm template?

2) If forced film is not used then it will tell TMPGENC to encode at 29.97 fps and you can select (S)VCD template? Does Doing it this way remove the need for a 3:2 pulldown.

The reason i ask is b/c I have one dvd player that supports 3:2 pulldown and the other one doesnt.

[Treebeard]

Anybody know if im correct in my assumptions?

[SingSing]

[quote="adam"]I don't think I could see a %5 difference, but ntscfilm compared to ntsc looks dramatically better to my eyes. [quote]

On large projection TV, flim rate SVCD look btter then NTSC's.

[fmctm1sw]

some will require the pulldown flag to be added, some won't, so adding the flag all the time is the best procedure.

As Adam stated, the gain comes from not encoding the "extra" frames, it is not necessary as they will be recreated in hardware.

Ok, so the deal is that you only have to encode 24 frames vice 30. The pulldown flag you mention though? Is that the 3:2 pulldown flag in TMPG (and others probably)? So I can inverse telecine, and select the 3:2 pulldown and I'll have a 20% potential gain in bitrate. I've been fooling around with this for a few days now and I have trouble with audio being TOTALLY jacked up after I IVTC. If I IVTC (been usin Vdub) with TMPG, will it handle my audio problem too?

[adam]

SLBOSS926

dvd2avi doesn't "tell" TMPGenc anything. Dvd2avi is a frameserver. It takes the source and sends it to the encoder exactly as it is, frame by frame. Of course you can modify the way it sends the signal.

By enabling forced film it disables, or possibly just ignores the RFF/TFF flag on the dvd which instructs the playback device to perform the real time telecine. So if you use forced film it will send the source to TMPGEnc as it is stored on the disk, which for most ntsc dvds will be 23.976fps progressive. And of course you should treat it accordingly and encode at 23.976fps. If you do not use forced film then dvd2avi will process the flags and you will get 29.97fps which you should also treat accordingly in your encoder.

Any svcd compatible dvd player accepts 23.976fps SVCDS with the 3:2 pulldown, at least I have never heard of any dvd player that can't. If you have problems with ntscfilm svcds then you have probably done something wrong. Vcds are another question, they do not support any pulldown flag but instead are supposed to be autotelecined by the player. Most vcd compatible dvd players have no problem doing this but some do it poorly or not at all.

[DJRumpy]

Snowmoon, or Adam hooked me up with PULLDOWN.EXE. Since I'm using CCE, I don't have the conveniance of a quick click solution in TMPGenc. Find it in the TOOLS section Wwwaaaay at the bottom, or just install DVD2SVCD. It's installed in that subfolder for you. I would also suggest you get the GUI for it. I don't know how many times I've screwed up and set the wrong aspect ratio, or forget to do pulldown. It's a time saver.

Speaking from my experience encoding VHS tapes. They look like crap in the telecined 29.97 fps. I used VirtualDub to IVTC back to 23.976 fps while capturing. The capture is much smaller, and allows higher bitrate do to the decrease in filesize. (Thanks again Snowmoon...I can now spot a telecined source, and determine the field order)

(Snowmoon, btw, I did finally find a newer version of that IVTC filter, and a high quality noise filter on the same sight that absolutely ROCKS! Very slow, but it doesn't introduce the blurriness/distortion that the other noise filters do).

[snowmoon]

What noise filter...

kRNC? or another

[DJRumpy]

I'm at work right now. I'll pull it up when I get home. The filter had a dll for AVSynth, and a plugin for VirtualDub. A quick search on Google once I get you the name should find it. It does impressive work on macroblocks, and general color distortions. I may still have the original zip, with URL info. I'll get back to you.

[DJRumpy]

The filter is from Donald Graft on mordor.net

http://sauron.mordor.net/dgraft/

The filter name is: smart smoother HiQuality (2.11)

I didn't realize it came from mordor.net. You probably already have it.

[fmctm1sw]

Not to beat this dead horse into glue, BUT: The 3:2 pulldown selection in TMPG. What exactly does that do? Does it convert from 24fps to 30fps (in which case I just wasted time converting to 24fps in Vdub) OR does it just add some kind of flag to tell my DVD player to perform the 3:2 pulldown itself (thus saving coverting 6 frames and speeding up the process, which is what I'm trying to do)?

[DJRumpy]

It converts your film to FILM (23.976 frames per second). It then adds a flag to the stream to tell you dvd player to convert the film back to 29.97 frames per second. Your player does this on the fly.

[snowmoon]

The Smart Smoother HQ was replaced by the much faster 2d optimized cleaner. It's like 4x the speed.

[nandi_nokuri]

I haven't seen anybody mention avs scripts for ITVC. If the framerate in DVD2AVI is 29.... and it says FILM, I have been ITVC'ing with an avs script. Should I be using Force Film ? I think I definitely need the script if I capture using my ATI AIW and DVD2AVI shows 29...NTSC Progressive. But I simply select the deinterlace filter in Tmpgenc when it shows NTSC Interlaced. I wish somebody will make an accurate chart showing what to do in certian situations when DVD2AVI says certain things. This link http://www.doom9.org/ivtc-tut.htm explains a little bit but you have to have a million hours on your hands to read it and then figure out what the heck to do. No offense to anyone, bit I personally don't care about the definitions I just want to know what to do in certian scenarios.

[DJRumpy]

Snow, the docs for the HQ cleaner tell you about the 2d cleaner, but they also warn you that you will lose quality to gain speed. The HQ filter is worth it if your going for the best Q you can get.

[adam]

I haven't seen anybody mention avs scripts for ITVC. If the framerate in DVD2AVI is 29.... and it says FILM, I have been ITVC'ing with an avs script. Should I be using Force Film ? I think I definitely need the script if I capture using my ATI AIW and DVD2AVI shows 29...NTSC Progressive. But I simply select the deinterlace filter in Tmpgenc when it shows NTSC Interlaced. I wish somebody will make an accurate chart showing what to do in certian situations when DVD2AVI says certain things. This link http://www.doom9.org/ivtc-tut.htm explains a little bit but you have to have a million hours on your hands to read it and then figure out what the heck to do. No offense to anyone, bit I personally don't care about the definitions I just want to know what to do in certian scenarios.

I think this has been explained numerous times on this forum. Preview the vobs and let it get past the opening credits. If it says FILM or %95 or higher film than use forced film....period. If it says ANYTHING else then do not use forced film. You will then have to either encode at 29.97fps or do an IVTC if applicable. That's all there is to it.

By doing an IVTC on your FILM sources you are essentially getting the same result as if you had used forced film, only it is taking you probably close to twice as long.

As for your captured sources, you cannot use forced film at all. Forced film disables the pulldown flags so obviously a captured source will not have these. If your source is 29.97fps progressive than you cannot do an IVTC. All you can do is encode at 29.97fps. If your source is 29.97fps interlaced than you may be able to perform an IVTC.

[nandi_nokuri]

Thanks Adam