DVDs: Progressive or Interlaced?

[atreya2011]

First of all, I would like to say that I have read the following FAQs before posting this novice question.

http://www.doom9.org/ivtc-tut.htm
http://www.dvddemystified.com/dvdfaq.html
http://nickyguides.digital-digest.com/interlace.htm

I would also like to quote this line from the DVD-Demystified DVD FAQ.


There's enormous confusion about whether DVD video is progressive or interlaced. Here's the one true answer: Progressive-source video (such as from film) is usually encoded on DVD as interlaced field pairs that can be reinterleaved by a progressive player to recreate the original progressive video.


The question is:

Why are some DVDs shown as interlaced in DVD2AVI? and Why are some DVDs shown as progressive?

(Since progressive video is always encoded on DVD as interlaced field pairs.)

[talkingjunky]

DVD2AVI is reading the MPEG2 flags to determine if the source material was interlaced video or progressive film. Non-standard encoded film material may show up in DVD2AVI as interlaced or mixed. That is why there is a Force Film option in DVD2AVI, which more-or-less ignores the MPEG2 flags and determines frames through 3:2 cadence.

This link has some good info how deinterlacers work and how various sources get transfered to DVD.

http://www.hometheaterhifi.com/volume_7_4/dvd-benchmark-part-5-progressive-10-2000.html

[neuron2]

Originally posted by talkingjunky
DVD2AVI is reading the MPEG2 flags to determine if the source material was interlaced video or progressive film. Non-standard encoded film material may show up in DVD2AVI as interlaced or mixed. That is why there is a Force Film option in DVD2AVI, which more-or-less ignores the MPEG2 flags and determines frames through 3:2 cadence. Actually, FF mode is useful only when the clip *is* standard encoded 3:2, not when it is 3:2 source encoded as interlaced (what you are calling non-standard). And FF does not use the 3:2 cadence at all. FF simply ignores the RFF flags and delivers just the MPEG encoded frames, skipping or duplicating them as required to maintain film frame rate (24fps).

DVD2AVI uses the presence and absence of RFF flags to distinguish film from video. It's not always correct because progressive content can be encoded as pure interlaced (no RFF flags).

[atreya2011]

Thanks for the reply neuron2, although I was able to understand what talkingjunky was talking about, I am not able to comprehend your explanation on the subject. Can you put it in layman terms. Thanks :)

By the way, what are RFF Flags?

[manono]

Hi-

If it's done properly, it's encoded as Progressive, the flags are set to output 29.97fps, and it's stored on the DVD at 24fps. That kind will show in DVD2AVI as Progressive/Film, and can be Force Filmed. This is neuron2's "standard encoded 3:2".

The inferior but still common enough way is to Telecine it to 29.97fps prior to encoding for DVD, encode it as Interlaced, and store it on the DVD at 29.97fps with no flag setting necessary. That kind will show as Interlaced/NTSC in DVD2AVI, cannot be Force Filmed, but can still be IVTC'd back to its Progressive source. This is neuron2's "3:2 source encoded as interlaced".

And there are also many different combinations and permutations of the 2 which can make life difficult for us encoders. Much of the anime out there is a prime example. Another is the huge number of bad PAL to NTSC conversion DVDs.

And, of course, this leaves aside truly interlaced material which is also encoded as Interlaced, cannot be Force Filmed, and can't be IVTC'd either.

The flags are programming or software put onto the DVD which tell the player how to output each frame, on a field-by-field basis. For more information on that and your RFF (Repeat First Field) question, please see Q8 of the DVD2AVI FAQ. (http://forum.doom9.org/showthread.php?s=&threadid=59272) And there's also more information on the subject right here on this site in Robshot's article. (http://www.doom9.org/synch.htm)

And I also highly recommend talkingjunky's link. It's a goldmine of information.

And neuron2, if I've put words in your mouth, or said anything incorrect, please set me straight. There's still much I have to learn about the subject, and no one knows this subject better than you. Much of what I've learned came from you to begin with, but anything stupid I may have said came from somewhere else (like from the depths of my fertile imagination).

[neuron2]

manono is my respected newbie-speak filter. :)

Looks good to me.

[atreya2011]

Thanks a lot, for the info manono. That makes a lot of sense now.

[Kika]

To make it complete: In PAL-World things are often different.
Her you can find interlaced Encoded progressive Frames on DVDs.
The normal way is to do a PAL-SpeedUp and to encode the Video in progressive Mode. But often interlaced Mode is used to encode such Videos. It does not really make sense, but that's the reality. :rolleyes:

[atreya2011]

"Interlaced encoded progressive frames?".

I thought "Telecide order=2" will be enough for a PAL Interlaced DVD since it will encoded as "1t 1b 2t 2b". Just when I thought I understood the explanation, it gets even more confusing. :confused:

[neuron2]

The order parameter can be only 0 or 1.

[Trahald]

@neuron2
since the topic is brought up.. ive always wondered what dvd2avi does when you have FF on but you dont have true 23.976 fps film source. it still spits out 23.976 fps (and 20 fps for pal), how does it decide what to remove? i figured since youve seen the guts you may have some insight.

[atreya2011]

The order parameter can be only 0 or 1.

Oops, my bad. I meant "Telecide order=1,guide=2"

Since PAL DVDs are encoded as "1t 1b 2t 2b", "Telecide order=1,guide=2" will be enough right?

[Kika]

@atreya2011

I talked about PAL-DVDs with progressive Video. Some of them are encodet in interlaced Mode, but that does not affect the progressive structure of the Pictures. So there's no need to use Telecide or something else.
What you are talking about are DVDs with PhaseShifts. On such DVDs, you have a (pseudo) interlaced Structure of the Frames.

[neuron2]

Originally posted by Trahald
[...] ive always wondered what dvd2avi does when you have FF on but you dont have true 23.976 fps film source. it still spits out 23.976 fps (and 20 fps for pal), how does it decide what to remove? i figured since youve seen the guts you may have some insight. IIRC, it keeps a running tally of how many frames it has emitted versus how many it needs to emit to maintain the film frame rate, and skips or duplicates frames as needed. Kind of like Bresenham's algorithm for line rendering.

[neuron2]

Originally posted by Kika
[...] Some of them are encoded in interlaced mode, but that does not affect the progressive structure of the pictures. True, but it does affect how any upsampling of the chroma should be done.

[atreya2011]

Originally posted by atreya2011
Oops, my bad. I meant "Telecide order=1,guide=2"

Since PAL DVDs are encoded as "1t 1b 2t 2b", "Telecide order=1,guide=2" will be enough right?

I am sorry for quoting myself but is the above argument correct?

[Kika]

@atreya2011

Since PAL DVDs are encoded as "1t 1b 2t 2b", "Telecide order=1,guide=2" will be enough right?

No, PAL-DVDs stored this way are progressive or true interlaced. In both cases you cant/should not use Telecide.

If you have one of those crappy DVDs with FieldShifts, Telecide should help.

@neuron2

True, but it does affect how any upsampling of the chroma should be done.

Yes, that's the point i forgot to post.