True Progressive DVD?
 

ADMIN NOTE: This thread was created from DVD spec posts from this original thread. Thanks, Tim Dashwood

Discussion here has been helpful. Have any conclusions been reached regarding 30p vs. 24p
towards the DVD end? I am still trying to ascertain whether source material shot at 24p and then converted for 30 fps viewing looks NOTICEABLY different than 30p source material viewed 30fps.
Would a 24fps DVD in a progressive scan machine be the true "filmlook" look. ( is this possible)?

It does look different, because the motion cadence is different. 30p is smoother (and by that I don't mean better or worse, just different).

A 24p DVD displayed progressively at 24 fps will have exactly film's MOTION, and also progressive frames (no interlacing, so higher resolution than interlaced video if done correctly). The "look," well, that's been debated exhaustively by many and means different things to different people.

Out of curiosity now, are there DVD players which can output a progressive video stream without converting it back to an interlaced signal, and progressive displays which can show that directly? In other words, can a home viewer using standard equipment get a true progressive image which hasn't been interlaced at some point in the process?

I think that the upcoming HD Disks will if using 720P, but currently DVD Players output a 3:2 cadence even when using an HDTV. I am not sure about this when using an upconversion player.

Have been for years. Any progressive-scan player will do this, and any progressive TV (generally HDTVs) will display it.

Every Hollywood DVD is 24p, except for some very early ones (which have no doubt all been reissued anyway).

Not so. Progressive-scan players do not (see my above post).

That only works for 24p right? It wouldn't really work for 30p because as far as I know 30p isn't in the DVD specs. You can encode a 30p DVD but a DVD player may not recognize it. I'm talking a true 30p DVD with the proper progressive flag set not a 30p source encoded as a regular 60i mpeg2 file. Even if a DVD was made with a 30p source when it sends it out the DVD player it would just think it was interlaced and therefore a digital display would end up pulling a bob. I thought I read somewhere that only 24p flags were recognized by players. I have been meaning to do a test and compare the results but I have not had a chance since I never shoot 30p.

30p isn't in the DVD spec. If you put a 30p file into an authoring program, it would be re-encoded as 60i -- whereas 24p files remain actual 24p files. There's no "progressive flag"; what there ARE are flags which allow for pulldown insertion by the player to make a progressive file interlaced for display on a standard TV.

Friends is at 24 fps!
 

Hi Laurence,

Unfortunately, you can't believe everything you read on the Internet! I just checked the DVDs myself (season 3 and season 10), and these guys are totally wrong. "Friends" is at 24 frames per second. The show has a 3:2 pulldown to make 60 fields per second. That, in turn, is encoded in a 29.97 Hz frame-rate MPEG sequence with 29.97 frame pictures per second (no use of the "repeat flags"). To add insult to injury, the show is not cut on film-frame boundaries -- meaning that the 3:2 pulldown "cadence" is not consistent throughout an episode or even within a scene.

But in short: these guys are wrong. "Friends" (at least seasons 3 and 10) is at 24 fps like almost every other prime-time narrative show and virtually every motion picture.

-Keith

Hi David,

Respectfully, I think this is not the case at all. Probably nobody here has read the actual confidential DVD specification, and certainly I haven't, but the widespread amateur understanding is that an "NTSC" DVD must consist of an MPEG interlaced sequence with a frame rate of 29.97. The formal result of the MPEG decoding process is therefore always 59.94 fields per second.

This still gives you several options for how to make those 59.94 fields. You can use 23.98 progressive frame pictures per second (like a DVD from a big Hollywood studio), using the "repeat flags" to produce the proper 59.94 fields. We could informally call this a "24p" DVD. You can have 29.97 progressive frame pictures per second (for "30p" source material), to produce those same 59.94 fields. Or you can have 29.97 interlaced frame pictures per second, again producing 59.94 fields (a "60i" DVD).

In short, "30p", "24p", and "60i" are all nominally supported by DVD, in that you can make a sequence encoded with the right number of interlaced or progressive frame pictures per second. If the question is about the formal output of the MPEG decoding process itself, than 60i is the only kind of MPEG sequence that is permissible.

Check out http://www.mpeg.org/MPEG/DVD/Book_B/Video.html for more information.

-Keith

Yeah, I'm sorry to pick on you, David, but this is just wrong. A normal DVD player outputs 59.94 interlaced fields per second. A progressive-scan DVD player outputs 59.94 progressive frames per second. For 24p source material, this will still generally result in a 3:2 cadence.

I'm not aware of any consumer-electronics DVD player (that one can buy) that will let you escape the 3:2 cadence. To do this, the player would have to extract the underlying MPEG frame pictures and output a 24PsF (48i) or 72Hz DVI signal, and then you would need a monitor that can refresh at 72Hz. I would love to be proved wrong, but I don't think you can actually get this setup without getting a PC and running a software DVD player on it, out to a 72Hz monitor.

I did once do a test on some HDTV "Law and Order" 24p material, where I played it back on a progressive-scan CRT monitor both at 60 Hz (with 3:2 pulldown) and then at 72 Hz (with a 3:3 pulldown, aka no 3:2 cadence at all). I went back and forth and back and forth between 60-with-pulldown and 72-no-pulldown, and to be honest it was extremely difficult for me to even tell the difference and identify which one was playing in a blind test. So my own opinion is that the 3:2 cadence, by itself, is not that big of a deal. But it is very hard to escape! :-)

-Keith

Hi, Keith --

In some ways, we're saying the same thing, in others, not so much.

When I say "60i," I of course mean 59.94i, so we don't disagree there.

However, if you were to go into a 24p DVD and pull the VOB files directly off the disc, you'll find that they are indeed 23.976p.

But you can't encode a 29.976p file to DVD; it will be re-encoded to 59.94i.

Think about it -- if everything had to be encoded ON DISC at 59.94, there would be no reason for a player to insert 3:2 pulldown on 24p files, because it would already be there.

Please note that the page you linked to makes reference to "the 2nd generation DVD MPEG-2 decoders WILL . . . " This page is really old.

As I mentioned above, Keith, this is a bit contradictory; if the video must be encoded at 59.94 no matter what, there would be no need for the player to insert a pulldown cadence of any kind.

In any case, I've been encoding and burning 24p DVDs in a professional capacity long enough to be quite confident in what I'm saying.

The easiest way to prove it, of course, is to step through frames and count them until a second ticks over. You get 24.

Also, if the player were outputting at 59.94p from a 59.94i file, you would see interlacing artifacts on 24p material where the B and C frames are mixed in a 3:2 (or 2:3) pulldown scheme. Again, you don't see this.

Has anybody here actually ever created a true 30p DVD and knows for sure they are getting a true progressive output from a DVD player?

On the DVD question:

DVD players are wonderful devices capable of reading MPEG streams that are true 24P or 60i. Some Chinese made DVD players also have PAL to NTSC and NTSC to PAL converters built in. You just need to know the secret code to configure the machine to your liking and then you can play DVDs from around the world on your own TV standard.

The point is that it is possible to encode a straight 24P Mpeg2 file for DVD. I do it all the time. A DVD player hooked up to a NTSC television will automatically add the 3:2 pulldown.
A progressive DVD player connected to a progressive display (or a computer DVD-ROM) will present the file progressively without adding pulldown.

I do not know if 30P or 25P can be flagged the same way, or if you just create a 60i or 50i (respectively) file with progressively scanned frames.

Yes, all the time, however the mpeg is always 29.97 even though the frames are progressive. 30p is in the spec (as well as 24p 60p and 60i).

Smet, try for yourself on your Liquid system. Create a DVD profile that is progressive and burn a DVD. Now pull the VOB back off the DVD you created and import it into the system. The file properties will ready 29.97 non interlaced. Component connected DVD players will push it out as progressive to flat panel TV's. No DVD authoring program will allow you to create a non standard DVD.

Have fun reading this Page

S.Noe

Thanks for that bit of info Stephen. You are the first person to ever give me a straight answer who has actually done it and tried it. I have been meaning to fake some true 30p footage but I didn't have the time. So you can really make a 60p DVD and it will play as 60i interlaced on a NTSC TV and 60p on a progressive display?

according to that link 60p is not supported.

Quite true. My bad. Anyway try the 30p. You should be able to get enough m2t's from the internet that are ProHD 30p to create the timeline.

I may just post an ISO so people can dissect it. Anyway, all DVD's are interlaced and it's the DVD player that reinterlaces the image to provide progressive if the TV will accept it.

OK, folks . . .

With enough people on here saying that all DVDs are interlaced and that all material on DVD is 59.94i, I pulled a VOB file directly from a DVD and screen-capped the file properties:

http://img93.imageshack.us/img93/9031/propsuf0.jpg

This is the data file taken directly from the DVD. It's a 24p file.

Hi David,

First, MPEG audio can't be the only audio on an NTSC DVD, so this doesn't look like a compliant NTSC DVD in the first place. See http://dvddemystified.com/dvdfaq.html#3.6 . Also, progressive_sequence isn't allowed either (http://dvddemystified.com/dvdfaq.html#3.4), so I think you maybe are getting misled by your authoring or analysis tools.

Could you please send me a slice of the VOB file (2 megabytes is fine) so I can take a look at the sequence header? keithw@mit.edu. I would appreciate it. Is this from a major studio or something you made?

As I said before, it's not that all material on a DVD is interlaced. It's that the MPEG sequence header indicates an interlaced sequence with a frame rate of 29.97 Hz. If you don't know what this means, then we probably are not disagreeing. As I said in my post, those 60 fields can be coded with 24 progressive frames (and the "repeat flags"), 30 progressive frames, 30 interlaced frames, etc. The DVD FAQ link (section 3.4) explains this pretty well, I think.

None of this should be foreign, though -- it is exactly what the JVC HD100 does. That is, when you have the JVC in 24p mode or 30p mode, it produces an MPEG-2 progressive sequence at a frame-rate of 59.94 Hz, with the "repeat flags" set to tell the decoder how to perform the pulldown. The subject of how a "24p" recording from the HD100 can be stored within a 60p MPEG-2 file has been discussed to death on this forum! :-)

Also, just to be clear, the single-step feature on a DVD is not indicative of the output of the MPEG decoding process. It probably just steps ahead by one coded MPEG picture. But in MPEG, by use of the "repeat flags," a coded picture can last for 1 field, 2 fields, 3 fields, etc. This is how the 3:2 pulldown is indicated by the encoder without having to code redundant information. Just because you don't see that when single-stepping doesn't mean it isn't there!

-Keith

If it wasn't compliant . . . it wouldn't play.

Or, alternatively, if it's not compliant, yet it still plays (which it does), then you can do what I say you can do, right?

But that's not the case. It's compliant. I think you're getting so caught up in the technical minutiae that you've completely lost the forest for the trees in what I'm saying.

(I mean, seriously -- my software's LYING to me? Would Occam's Razor really lead you to that conclusion?)

...In the red corner, wearing red trunks with white trim...

David,

I think this subject (of "repeat flags" and how 24 coded progressive frames can be stored inside a 29.97 Hz interlaced MPEG-2 sequence) has already been talked to death on this forum, and I'm sorry we didn't successfully communicate. It's not that your software is lying to you; it's that "24p" can mean two different things, as I struggled to explain above and repeatedly.

The links I gave to the DVD FAQ explain, far better than I can, the questions of compliance (and whether you can have only MPEG audio on an NTSC DVD) with a confidential specification neither of us has read.

If you really want to continue this, the best way would be for you to name ANY commercial NTSC DVD release that you believe to be a true 24p MPEG-2 video with no 3:2 cadence, and I will go out and buy it and look at the MPEG. Alternately, you're still welcome to e-mail me the VOB file ripped from the DVD you made, or post it on the Web and send us the URL.

-Keith

Keith, try Fight Club, or any other major Fox release professionally encoded by deluxe or dvcc.

I know where you are coming from and the DVD FAQ is a great resource (even though some of the stuff is a little out of date.)
However, when I export a NTSC-DV 23.98fps file from FCP (not a 24P project with 3:2 pulldown in a 29.97 file, but true 24P) and then encode it with compressor as 23.98fps, the file I get is a 23.98fps MPEG2. This is how I've authored my DVDs for the past three years and as far as I can tell 23.98 is a valid Mpeg2 frame rate.
When I play the DVDs I create in a non-progressive DVD player connected to a NTSC monitor, the DVD player adds the 3:2 pulldown for me.
Yes, most "progressive" DVD players have the ability to detect 24P within a 3:2 pulldown 29.97 mpeg2 and ignore the pulldown fields, but I'm quite certain that is not what's happening here. If it were, then in my scenario Compressor would have to add the pulldown frames. I don't think it does.

I really want to find the truth of the matter.

Attached is one chapter I ripped and checked "info" with Quicktime 7.1

Hi Tim,

I have great respect for your cinematography, and I very much appreciate your stewardship of the HD100 forum, so just wanted to say thank you.

In this case, it looks like Quicktime has been making things too "nice" and obscuring the details of the MPEG-2 files. I agree with you that 23.98 fps progressive sequences are legal in MPEG-2 (in fact, they're legal on ATSC broadcasts, even though nobody uses them). But everything we know about the confidential DVD specification suggests that they're not legal on DVDs.

I went and got "Fight Club" out from Blockbuster, and it, too, is a 29.97 Hz interlaced MPEG-2 movie. Fox/deluxe have economically only used 24 coded pictures per second to make those 59.94 fields, and they've used the "repeat flags" to signal to the MPEG decoder that some pictures should last for 3 fields, and some should last for 2 fields.

So a smart DVD player or editing tool can certainly extract the original 24 coded pictures, and in that sense it is a "24p" MPEG-2 file (just like the JVC HD100 makes). In another sense, a formal MPEG-2 decoder will produce 59.94 interlaced fields per second, and in that sense it's a "60i" MPEG-2 file. A consumer "progressive-scan" DVD player will produce 59.94 progressive frames per second, retaining the 3:2 cadence but not the interlacing.

Here's the output of running mpeg2dec -v on the beginning of chapter 32 of "Fight Club". The "SEQUENCE" line tells us the resolution of the luma and chroma (720x480 and 360x240, since it's 4:2:0) and the frame-rate (29.97). If this were a progressive sequence, it would say "PROG" in the sequence header. In the "PICTURE" lines, the number after "fields" tells us how many fields the picture is supposed to be repeated for. Remember that the pictures are sent out-of-order -- you can look at the "time_ref" field to see the position of the frame in display order. And, of course, the sequence is coded entirely with progressive pictures even though it's an interlaced sequence.

I'm curious what Quicktime has to say about this file. I posted the beginning (after decrypting it) at http://web.mit.edu/keithw/www/fight_club.mpeg2ps if you want to run it through your tools.

Regards,
Keith

a8 SEQUENCE MPEG2 MP@ML 720x480 chroma 360x240 fps 29.97 maxBps 1225000 vbv 229376 picture 720x480 display 720x480 pixel 32x27
113 GOP DROP CLOSED 2:56:34:27
127 PICTURE I PROG fields 3 TFF pts 013bcdd9 dts 013bc21e time_ref 0 offset 0/0 0/0 0/0
16127 SLICE
1613f PICTURE P PROG fields 2 TFF time_ref 3 offset 0/0 0/0
2225f SLICE
22277 PICTURE B PROG fields 2 time_ref 1 offset 0/0 0/0
273bf SLICE
273d7 PICTURE B PROG fields 3 time_ref 2 offset 0/0 0/0 0/0
2c25f SLICE
2c277 PICTURE P PROG fields 3 time_ref 6 offset 0/0 0/0 0/0
324db SLICE
324f3 PICTURE B PROG fields 3 TFF time_ref 4 offset 0/0 0/0 0/0
377d3 SLICE
377eb PICTURE B PROG fields 2 time_ref 5 offset 0/0 0/0
3caf7 SLICE
3cb0f PICTURE P PROG fields 2 time_ref 9 offset 0/0 0/0
43067 SLICE
4307f PICTURE B PROG fields 2 TFF time_ref 7 offset 0/0 0/0
48adf SLICE
48af7 PICTURE B PROG fields 3 TFF time_ref 8 offset 0/0 0/0 0/0
4e847 SLICE
4e85f PICTURE P PROG fields 3 time_ref 10 offset 0/0 0/0 0/0
5abfb SLICE
5ac13 PICTURE P PROG fields 2 TFF time_ref 11 offset 0/0 0/0
66123 SLICE

I checked the file you uploaded and both MpegStreamclip and Quicktime said 23.98fps.

So I'm still a little confused from your explanation.
My simple question is: Is the original file physically 23.98fps and your decoder is adding the 3:2 pulldown while it plays, or are all Mpeg2 files encoded for NTSC DVD always 29.97fps, regardless of flags?


Curiously, when I look at a 720P24 HD100 m2t in Mpegstreamclip it only displays the 24 flagged frames when stepping through frame-by-frame (you can tell by the TC readout,) but the frame rate still shows 59.94 when I look at the stream info. When I looked at your mpeg2 from Fight Club it didn't skip any frames and showed 23.98, which once again leads me to believe that the physical mpeg2 has 23.98 frames, and the decoder adds 3:2 pulldown when necessary.

Agree? Disagree?

I'm sorry not to have a clear answer -- those are both arguably correct. I would say that the MPEG-2 file on a Hollywood DVD "physically" consists of three things:

(1) An MPEG-2 sequence header telling the decoder that the output is 59.94 interlaced fields per second.

(2) A sequence of 24 progressive pictures per second (the same pictures that were recorded on the film and shown in theaters).

(3) For each picture in the file, a number ("2" or "3", aka the "repeat flags") instructing the MPEG decoder (the DVD player) for how many fields the picture should last. For example, "2" for the first picture, then "3" for the second picture, etc.

A normal DVD player will read the file, decode the 24 progressive pictures per second, and then obey the number in the MPEG-2 file that tells us how many fields to repeat each picture. So, the DVD player *is* the one adding in the pulldown, but it's not doing so "automatically" -- it's doing so because the MPEG-2 file instructs it on exactly how many fields it's supposed to repeat each picture, and it's just doing what the MPEG decoding process requires.

So, if you're asking how many separate pictures were actually included per second, the answer is 24. If you're asking what the MPEG-2 file produces when decoded, the answer is 60 interlaced fields per second. The "pulldown" and 3:2 cadence *are* physically on the DVD, but they're not in #2 (above), they're in #3 (the numbers that tell the DVD player how many times to repeat each picture).

I hope this clears it up... does it?

As for Mpegstreamclip, I agree that those results seem inconsistent. I don't know why it gives 23.98 for the Fight Club MPEG-2, but 59.94 for the JVC's MPEG-2. It seems like maybe Mpegstreamclip is too smart for its own good (trying to detect whether it's a "24-within-60" file) and ends up giving confusing results? Not sure, sorry.

HI David Jamerson
Have you worked out a work flow for starting wit 25iPal, and creating a 24p dvd in Vegas? Can US dvd players play a 24p pal dvd
Will you have to just take the 25i slow it down to 24p, and then standards convert? Are there any options to up convert the pal to a HD level using software ( so you don't loose the 100 extra lines of vert res)

Sharyn