True Progressive DVD?

[Hayes Roberts]

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)?

[David Jimerson]

Originally Posted by Hayes Roberts

Jaadgy, nicely expressed.
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.

[Kevin Shaw]

Originally Posted by David Jimerson

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).

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?

[Steve Benner]

Originally Posted by Kevin Shaw

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.

[David Jimerson]

Originally Posted by Kevin Shaw

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?

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).

[David Jimerson]

Originally Posted by Steve Benner

but currently DVD Players output a 3:2 cadence even when using an HDTV.

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

[Thomas Smet]

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.

[David Jimerson]

Originally Posted by Thomas Smet

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.

[Keith Winstein]

Originally Posted by Laurence Kingston

I just did a google search and found that "Friends" is shot on film at 30p and released on DVD as 30p video that is flagged as 60i.

http://www.hometheaterhifi.com/volum...e-10-2000.html

"Several TV shows, including Friends, are shot on 30 fps cameras and transferred to video using 2-2 pulldown. Unfortunately, the Friends DVDs are not marked progressive, which just reinforces our point – you can’t trust the flags."

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

[Keith Winstein]

Originally Posted by David Jimerson

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.

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

[Keith Winstein]

Originally Posted by Steve Benner

currently DVD Players output a 3:2 cadence even when using an HDTV.

Originally Posted by David Jimerson

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

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

[David Jimerson]

Originally Posted by Keith Winstein

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

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.

[David Jimerson]

Originally Posted by Keith Winstein

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

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.

[Thomas Smet]

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?

[Tim Dashwood]

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.