Progressive Scan DVD Players - Why necc?

[surreal120]

I know I'm probably missing something really obvious, so I apologize for asking a dumb question but here goes:

If I have a DVD - which is non-interlaced and 29.97 fps - and am watching it on an HDTV, why do I need a progressive scan DVD player? In other words, if the DVD isn't interlaced and has already been pulled down, shouldn't the dvd player just feed the frames right to the TV? Why would I need a special progressive scanning dvd player and what exactly would it be doing?

[manono]

Hi-

You might not need a Progressive Scan DVD Player if your HDTV has good 3:2 pulldown detection. In that case your regular DVD Player will feed 480i to the TV set for conversion to progressive. For example, my Samsung has the Faroudja chip for doing that. If yours doesn't do 3:2 pulldown detection, or if it's inferior to the one in your Progressive Scan DVD Player, then having such a DVD player will mean a definite step up in picture quality.

All DVDs are encoded to send 29.97fps interlaced to the TV set. But if it's encoded as Progressive, then either a Progressive Scan DVD Player, or the HDTV with 3:2 pulldown detection can return the video to its original 24fps Progressive, which is what you want. If it's not encoded as progressive, then, depending on the quality of the chip that the Progressive Scan DVD Player uses, you'll get better or worse results. That is, not all Progressive Scan DVD Players are created equal.

In other words, if the DVD isn't interlaced and has already been pulled down, shouldn't the dvd player just feed the frames right to the TV?

Nope, for the reasons I explained above. DVDs were developed for standard interlaced TV sets, and because of that, feed them 59.94 fields per second, rather than 24 frames per second.

If you make your way through this link (it's very long, but chocked full of information):

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

then among other things, you'll come across this paragraph:
Progressive displays, such as high-performance CRT/LCD/DLP/LCOS projectors and the new HDTV-ready TVs, can show progressive scanned images as opposed to interlaced. We learned above that an interlaced display shows 60 fields per second. But with progressive, each scan of the CRT face is a complete picture including all scan lines, top to bottom, now called a frame, and we are showing 60 of those per second. The benefits of a progressive display are no flicker, scan lines are much less visible (permitting closer seating to the display), and they have none of the artifacts we described for the interlaced display (as long as they are fed a real progressive signal).
and this one:
A common question we get asked is, "Why can't the DVD player just take the progressive frames off the disc and send them out without ever converting them to interlaced in the first place?" The reason, in a nutshell, is that there are too many examples of discs where some or all of the frames are not stored progressively. Even if the original material was sourced from film, there is no requirement at all that the frames be stored like Example 1, above. It's relatively common for films to be dumped onto the disc using an encoding similar to Example 3. As mentioned before, most major Hollywood releases look more like the first example, but it's just that they have better encoding software, which recognizes the 3-2 pattern and removes the extra repeated fields for compression efficiency. It's not done to improve progressive playback; that just happens to be a useful side-effect.
But that link should answer all of your questions, except maybe which Progressive Scan Player to buy. For that, you might be interested in this comparison:

http://www.hometheaterhifi.com/cgi-bin/shootout.cgi?function=search&articles=all

And if your display has DVI in, then you'll definitely want to take advantage of that by buying a DVD player with DVI out. It means another step up in picture quality, because you can then avoid the digital to analog conversion(s). There aren't to many yet, but more are on the way.

[surreal120]

Okay, I'm still a little confused though. First, THANKS for that article! - I had completely misundertood telecining before.

Allright, so if DVDs that you buy in a store are really stored as interlaced fields, then what does DVD2AVI mean when it says the video is Progressive but also 29.97fps?

[jggimi]

AFAIK, DVD2AVI uses the MPEG-2 flags to determine frame status, which are part of the DVD's encoding process. That's why you can use Force FILM with some Telecined DVDs, but not others -- the video streams may be equivalent, but the flags do not report the same status.

[manono]

Hi-

so if DVDs that you buy in a store are really stored as interlaced fields...

They may be or they may not be, or it may be a combination of the two. But they are all output as 29.97fps. If the film or part of it is stored as 24fps progressive, then as jggimi implied, the flags tell the player to output 29.97fps (really 59.94 fields per second, since standard TV sets can display only fields). There's no way around that step. But a Progressive Scan DVD Player, or the display if it has 3:2 pulldown detection, can undo that step and convert it back to 24fps for display on a Progressive HDTV. Even the cheapest flag reading Progressive Scan DVD players can output progressive frames which have been encoded as Progressive (shown as FILM in DVD2AVI). The better ones can output progressive frames that have been encoded by other methods.

Here's another article, available on this site, that explains a bit about how they're encoded:

http://www.doom9.org/synch.htm,

and in there you'll find this paragraph:

A good thing about Mpeg-2 Video is that it can contain some FLAGS or PROGRAMMING, that would tell a SOFTWARE or HARDWARE to perform a TELECINE when playing the Video. Since the INTERLACED FRAMES that made-up the 29.97fps is a REPEATED field(s), it is REDUNDANT, and TRASHABLE. Just let the FLAGS tells the player to perform the TELECINE. Really, it CAN do that ;). The benefit of this that the movie CAN be stored in its original 24 FRAME per second, and thus SAVE 20% of total filesize!.
And there's always the article that jggimi and I had a hand in writing (shameless plug):

http://www.doom9.org/ivtc-tut.htm

This is tough stuff to get a handle on. Don't be discouraged that you haven't mastered it after an hour of reading.

[surreal120]

Thanks for the help guys! I think I have a much better handle on this already, but I will definitely read the DVD2AVI guide you mentioned (I actually find this stuff pretty fascinating!).

Again, thanks.