Need clarification on DVD fps

[windsor]

Hi all. First time posting. :) I've searched several forums and went through the FAQs here but was unable to find a definitive answer to my question. I apologize for my ignorance if this has been asked many times.

I'm a DVD2SVCD newbie and wondering how I can determine the fps of my DVD. My understanding is that if the DVD is pure 30 fps, DVD2AVI will easily strip out markers to reduce the video to 24 fps. If it fluctuates between 24 and 30, DVD2AVI will do IVTC. If it's already at 24 fps, then DVD2AVI does no conversion. Is this correct? Are most DVD's at 24 fps?

Thanks for reading my post. :) Any input appreciated.

[Slogra]

I had this same problem some time ago.

PowerDVD will always show 29,97 fps, so it's useless when you want to check fps.

Most movies are 24fps. TV shows are often 29,97 interlaced. Animes can be anything.
Normally you can set " NTSC Field Operation (Force film)" to "Automatic" at the DVD2AVI tab. But i noticed this doesn't work like it should all the time (it didn't work on a anime i encoded although it was 24fps afterall).
So the best thing that you can do is to do a test on only one chapter of the movie. So go to the Conversion tab and click Movie length and deselect all chapters and select only the shortest chapter.
Encode this with Automatic force film and check the outputted mpeg for interlaced lines in PowerDVD. If it has lines you have to use IVTC (Slow as hell). And if that doesn't work your DVD might be truely 29,97interlaced, in that case you have to select a deinterlace method at the Conversion tab.

You can also check if the movie is 24fps with Gordian Knot, which is explained in this thread by manono: http://forum.doom9.org/showthread.php?s=&threadid=54924

He says:
I haven't worked with .Hack, but most anime can be IVTC'd. Nowadays a lot of them have 29.97fps passages, but I usually ignore it. In any event, you can find out easily enough if it's really 23.976fps. Take the .d2v that DVD2SVCD made for you (with no Force Film) and open it in GKnot (you have that installed?). Then find a place where there's movement and start advancing frame by frame. If you see 2 out of every 5 frames interlaced (as Wilbert said), it has been telecined and can be IVTC'd. But if all the frames are interlaced, it can only be deinterlaced. You want to bring it back to 23.976fps if possible, because of the better quality you'll get from encoding 20% fewer frames.

How do i know the output SVCD is 23,97 fps or 29,97fps? WinDVD always indicates 29,97fps with all my experiments.

The only sure way to tell what the source is, is to look at the frames. But all NTSC DVDs and SVCDs put out 29.97fps because of the flags that get set during pulldown telling the player how to output 29.97fps.

[windsor]

Hi Slogra,

Thanks very much for your reply. It really cleared things up. :) I see determining the fps of a DVD is not straightforward, especially when dealing with anime. Unfortunately the concepts of interlacing, aspect ratios and fps are still confusing to me. I wish there was some tool that could just output this information neatly in one window (if it's possible).

So far, my understanding of these topics are outlined as follows:

- If the source is 24 fps, it has progressive frames. If the source is 30 fps, it has interlaced frames and DVD2SVCD should automatically do a 3:2 pulldown (as opposed to 2:3) before encoding with TMPGEnc/CCE.

- Some videos fluctuate between 24 and 30 fps and therefore you may have to manually determine if it's better to IVTC or not.

- Encoding an SVCD as anamorphic (no black borders) even if the source is not anamorphic will allow more bits for moving video as long as you resize it correctly. However, many players do not support anamorphic SVCD's and will not letterbox the output accordingly.

- If the SVCD is encoded correctly at 24 fps, the player will output at 30 fps (60 Hz) to a standard NTSC TV.

- The benefits of progressive frames are only evident on digital widescreen TV's.

Are the above points valid?

Also, I found this page on the web that says it's never worth it to deinterlace for SVCD's, no matter if the source is progressive or interlaced.

http://www.inwards.com/~dbb/interlace_myths.html

[Slogra]

- If the source is 24 fps, it has progressive frames. If the source is 30 fps, it has interlaced frames and DVD2SVCD should automatically do a 3:2 pulldown (as opposed to 2:3) before encoding with TMPGEnc/CCE.

When a player plays a 24fps movie, it must add a few frames so it will be NTSC compatible (29,97fps, 60hz). This is called 3:2 pulldown or Telecide. IVTC means inverse telecine which is used if you want to go from 29,97 back to 24fps.

Yes, most 29,97fps DVDs are interlaced, so you can deinterlace so you'll get 29,97 progressive frames. Or keep it interlaced so it'll be 29,97 interlaced (60hz).

- Some videos fluctuate between 24 and 30 fps and therefore you may have to manually determine if it's better to IVTC or not.

Eh, this is a hard one... i guess you can say that. It will probably be 24fps, but SVCD doesn't always detect it the right way. So that's why there are a lot of options at the DVD2AVI tab at NTSC Field Operation to fix it.
Automatic: this should automaticly detect if it's 24fps or 29,97 intelaced. Try On if this didn't work.
On: This will give you a 24fps movie. But the ITVC process can be screwed up. Try ITVC is this didn't work.
ITVC: It will check the frames in the movie more thoroughly, so you get a perfect 24fps, but the encoding process will slow down.
Off: This might be usefull if you want to keep 29,97 interlaced and On didn't detect it the right way, or something...

- Encoding an SVCD as anamorphic (no black borders) even if the source is not anamorphic will allow more bits for moving video as long as you resize it correctly. However, many players do not support anamorphic SVCD's and will not letterbox the output accordingly.

I would never make a SVCD anamorphic as it uses more pixels and it will be harder to encode properly. It's smarter to use "16:9 (borders added, encoded as 4:3)" when you want to convert an anamorphic widescreen DVD.
I'm sure there is a good explenation of anamorphic on this site so i'm not going furter into that.

- If the SVCD is encoded correctly at 24 fps, the player will output at 30 fps (60 Hz) to a standard NTSC TV.

Software players like PowerDVD on your pc will show the content at 24fps progressive (which simply means not interlaced). A pc monitor is progressive while a tv is interlaced.

But almost all standalone players will always output 30fps interlaced, because a TV needs 30fps NTSC. This looks much uglier than 24 progressive.
However some new players can show 24fps progressive (not interlaced). If you also have a tv that can handle progressive input, then the picture will just as sharp as on your pc. This will cost you a lot of money. K'ching!

- The benefits of progressive frames are only evident on digital widescreen TV's.

I kinda explained at the previous question. You'll need a progressive TV and progressive player or a PC to really enjoy 24 encoded stuff.

Besides great visual quality, there is the benefit that the DVD or SVCD will only need to store 24fps instead of 30. So less space is wasted.


Also, I found this page on the web that says it's never worth it to deinterlace for SVCD's, no matter if the source is progressive or interlaced.

Yes and no.
With 29,97 interlaced videos there is not much to be gained by deinterlacing it. So you can keep it interlaced.
But you should ALWAYS use IVTC (some might call it deinterlace, which is not the right word) on 24fps progressive DVDs. You will gain a lot of quality in your SVCD.

[mic]

Using DVD2AVI I've always followed advice (from orig. docs I think) of doing a preview with forced frames set to none. The info dialog will show it's guess re: if the video is film (24 fps prog.). Newer versions of DVD2AVI though show up in V/Dub thru vfapi as 23.97 fps, so be careful when setting frame rates in other software or audio sync etc. can suffer.

As Slogra posted, the player determines the correct playback fps and does it's job accordingly.

IF it helps, the higher frame rate you have, the smoother the video will look, but the encoded file size gets bigger to match. I only mention this because I've read of a LOT of folks who are disatisfied after doing ivt, wondering why going from 29.97 down to 24 can make motion and/or panning scenes less smooth.

Regarding the debate whether to go anamorphic or not, one additional point to consider... Every time you alter a video, you loose some quality - one reason frame-serving and such are popular. If your player can handle it, going direct from DVD2AVI to encoding without altering anything might preserve a bit more quality then taking the added step of resizing. Now whether the slight quality hit is enough to worry about is a matter of personal preference.

Interlacing is best explained IMO here: http://www.100fps.com/

As a set top DVD player will interlace your SVCD for your tv anyway, removing it only adds the benefit of smaller file sizes whilst adding some blurring from combining fields. The same could be said for IVT more or less, as it's not always perfect. Playback on a PC or progressive TV monitor is another story, as often the telecining artifacts can be noticed.

I think Slogra had a typo at the end of the last post, as certainly everything else was right on - HBO for example might take a 24 fps prog. film and have it run through a telecine process to add additional frames and fields to make it compatible with standard TVs. A DVD having the original 24 fps prog. movie has not had any telecining done to it, so there's nothing to remove. For a more complete explanation: http://www.zerocut.com/tech/pulldown.html

[adam]

Originally posted by mic
IF it helps, the higher frame rate you have, the smoother the video will look, but the encoded file size gets bigger to match. I only mention this because I've read of a LOT of folks who are disatisfied after doing ivt, wondering why going from 29.97 down to 24 can make motion and/or panning scenes less smooth.


But assuming the IVTC was done properly, ie: proper source and proper fields removed, there is literally no difference at all in the smoothness of motion. Either way its still being played at 29.97fps, one has just undergone a hard telecine and the other a soft telecine.

Unless you are referring to pc playback?

[mic]

You've said it all: "...assuming the ivt was done properly"

Some prog work better then others, some movies are done with 2 or 3 telecine methods, and some broadcast programs never were progressive 24 fps. In the complaints I've read, Usually someone just checks IVT in whatever prog dialog box, goes on with the project without ever checking anything, then gets upset because it doesn't look as wonderful as they expected, sometimes on a TV, sometimes on a PC.

I guess I was just trying to temper the expectations of anyone trying it for the first time.

[Slogra]

Originally posted by Slogra

Yes and no.
With 29,97 interlaced videos there is not much to be gained by deinterlacing it. So you can keep it interlaced.


Originally posted by mic

I think Slogra had a typo at the end of the last post, as certainly everything else was right on - HBO for example might take a 24 fps prog. film and have it run through a telecine process to add additional frames and fields to make it compatible with standard TVs. A DVD having the original 24 fps prog. movie has not had any telecining done to it, so there's nothing to remove.


That's not a typo. I was talking about real 29,97fps interlaced stuff with 60 different fields. While you are thinking of telecined stuff.
So we're both right :D

[windsor]

Thanks guys, very much appreciate all your informative posts. You've all been immensely helpful in filling the gaps in my head. Not wanting to trouble you any further, I only have three more questions before I have a basic understanding on how everything works.

Firstly, I was wondering what exactly does Force Film do to the video stream? On a 24 fps DVD, one guide says "3:2 pulldown markers are removed and frames are restored progressively" while another one says "pulldown flags are added so the DVD player will output the SVCD at 30 fps." Which one is correct or are they both correct?

Also, the inwards.com guide that I linked to in my second post says 16:9 anamorphic movies must be IVTC'd in order to resize properly. Why would that apply if the DVD is already at 24 fps? Wouldn't you just resize once and be done?

Slogra wrote, "When a player plays a 24fps movie, it must add a few frames so it will be NTSC compatible (29,97fps, 60hz). This is called 3:2 pulldown or Telecide." Did you mean telecine instead of telecide?

Anyway, I just wanted to add three notes about the guides I've come across as a newbie.

- when authors write 3:2 pulldown they always seem to mean 2:3 pulldown instead

- some guides lump Force Film as a form of IVTC. That makes the reading a lot more confusing. :(

- there's no easily accessible guide that explains what the applications of DVD2SVCD actually do. I think it'd be helpful to have such a guide in order to better understand the concepts behind rip/encoding and output better rips. All the guides I've seen (including ones directly linked from DVD2SVCD home page) focus more on the motions of making a rip. The DVD2AVI FAQ in the DVD2AVI forum doesn't even explain what DVD2AVI is nor what a d2v file contains.

Oh well. Thanks, you guys are :cool:.

[adam]

Originally posted by windsor
Firstly, I was wondering what exactly does Force Film do to the video stream? On a 24 fps DVD, one guide says "3:2 pulldown markers are removed and frames are restored progressively" while another one says "pulldown flags are added so the DVD player will output the SVCD at 30 fps." Which one is correct or are they both correct? The first little quote you listed is correct, the second seems to be referring to the 3:2 pulldown flag, not the forced film function. As already stated, the film is stored at 23.976fps on the DVD, and RFF/TFF (3:2 pulldown) flags are embedded in the stream which instruct the dvd player to telecine the movie as it plays. Forced film simply ignores this flag, giving you the 23.97fps progressive frames as they are stored.

Also, the inwards.com guide that I linked to in my second post says 16:9 anamorphic movies must be IVTC'd in order to resize properly. Why would that apply if the DVD is already at 24 fps? Wouldn't you just resize once and be done? I haven't read that guide, but it seems to me it is clearly talking about an actual IVTC, where the source has been telecined to 29.97fps, and not the forced film option in dvd2avi.

when authors write 3:2 pulldown they always seem to mean 2:3 pulldown insteadIt is my understanding that there is no difference. They are just two different names for the same thing. All these names refer to are the number of repeated fields relative to the number of fields left alone when film is telecined using this very common pattern. It just depends on where you start counting, but the effect is the same. TMPGEnc calls its flag 3:2 and pulldown.exe calls it 2:3, and most technical documents refer to it as 2:3, but ultimately it really doesn't matter.

- some guides lump Force Film as a form of IVTC. That makes the reading a lot more confusing. :(I agree entirely. In my mind something cannot be inverse telecined unless it has been telecined first. When a typical NTSC DVD is used as a source, it is never telecined at all. You skip this unneccessary step entirely, rather than undo it later. Just read guides with a grain of salt.

[Slogra]

Originally posted by windsor
Did you mean telecine instead of telecide?

Yes, i meant telecine

Originally posted by windsor

- there's no easily accessible guide that explains what the applications of DVD2SVCD actually do. I think it'd be helpful to have such a guide in order to better understand the concepts behind rip/encoding and output better rips. All the guides I've seen (including ones directly linked from DVD2SVCD home page) focus more on the motions of making a rip. The DVD2AVI FAQ in the DVD2AVI forum doesn't even explain what DVD2AVI is nor what a d2v file contains.

Agreed, we need a good DVD2SVCD guide. Maybe you should start a new topic about this and refer to this post, as this post is getting old and hard to find :p. Maybe you can write one as you figured most things out :D .
I'm not such a good help writer, cause i probably forget a lot of important stuff and not to mention my bad engrish and typing (telecine/telecide).