24P or 30P for DVD?

[Alex Humphrey]

Originally Posted by Jarrod Whaley

Spatial resolution is the same either way, because no one is looking at the screen for only 1/60 of a second. :) 60i's only spatial resolution disadvantage is that you lose a lot of res when deinterlacing (if desired and/or necessary). 60i's temporal resolution is actually twice that of 30p.

Well, nothing is truly progressive on an NTSC monitor, because NTSC is interlaced by definition; in order for anything to play in NTSC, some kind of interlacing is necessary--either directly applied to the footage (as with 30p), or in a "meta" sense in the form of pulldown (as with 24p).

DVD players insert pulldown (or "pullup") in order to play a 24p disc, because it is necessary to do so in order to fit 24 frames into 60 interlaced fields. But 30 progressive frames fits evenly into 60i, so no pulldown is necessary. Because of that, cameras record 30p to tape in a 60i stream, and there's no easy way to extract those frames and work in a 30p timeline, whereas you can do just that when editing 24p. Furthermore, DVD authoring software typically offers no project templates for 30p, because the standard 30p workflow is built around 30p being embedded in a 60i stream. While it is theoretically possible to author a 30p DVD, of course, the usual post-production software routes do not offer the option to export 30p in any way other than as a 60i stream. As far as I know, at least. I am not 100% sure, but I suspect that a true 30p disc would not play back on an NTSC DVD player. The players are designed to add pulldown to 24p, because that's the way Hollywood does it. But as far as I know, interlaced players are not equipped to play 30p back as NTSC-compatible video.

For the most part, the difference is purely academic anyway, because the results look pretty much exactly the same either way. The main difference is that 30p pretty much has to be encoded to MPEG-2 as 60i, and thus requires more encoding bandwidth than honest-to-god 30p would.

At the end of the day, none of this is as important as what looks best to you, or what works best for the project. But it's helpful to understand how all of these frame rate things work, because it allows you to make more informed decisions.

well, this thread is a year old, but what the hell. I just went through tons of experiments, and I can say 30p exported to dvd looks much better than a sd dv camcorder, however, it looks nothing like a store bought movie from Universal. I tried 24p (HDV from a JVC HD110) edited 24p in FCP, out to compressor to mpg2 at 23.97. BAM. big difference! Looked 90% as good as most HD broadcast. It looked like a pretty good universal/Sony pictured store bougth DVD. So honestly, I'm going to try to shoot everything at 24p for a while and see how it holds up. Of course I have 20 hours of footage to edit and encode at 30p, and now I don't want to. So if you don't want the interlacing and artifacts of taking 30p and making a 59.97i DVD or a 23.97i (progressive like with DVD pulldown) then take your 30p footage, drop it into FCP in a 60p DVCPRO50 timeline, then export from there to mpg2 23.97 file. This method gave the encoder a wider choice to take 60p and turn it into 24p than to take 30p into 24p. not as good as shooting 24p to begin with, and huge rendering times, but significantly better than 30p to 59.97i or 23.97i were the interlaced frames don't line up together correctly when output from the DVD player in progressive mode. Odd wavy lines and compression artifacts durring movment.

[Michael Jouravlev]

Originally Posted by Jarrod Whaley

Well, nothing is truly progressive on an NTSC monitor, because NTSC is interlaced by definition; in order for anything to play in NTSC, some kind of interlacing is necessary--either directly applied to the footage (as with 30p), or in a "meta" sense in the form of pulldown (as with 24p).

This depends on your definition of NTSC. Technically, NTSC is the way of encoding color into analog television signal. As such, only analog TV sets are true NTSC TVs. Digital plasma/LCD/projection/whatever TVs are NOT NTSC devices. With this definition of NTSC you are correct.

On the other hand, if by NTSC you mean the whole shebang of North-American television standards, either analog or digital, with 525 (full, analog) or 480 (digital) scan lines, than you are wrong. Flat-panel digital TVs are all progressive except Hitachi/Fujitsu which are sort of interlaced, they packed more lines in their panels, but could not control them in truly progressive manner. The signal itself can be progressive too, be it 480p. 720p or 1080p with 24, 30 or 60 fps. Well, ok, the new digital standard is called ATSC not NTSC, so your statement that NTSC cannot be progressive still holds true technically, but for most people this would sound like a fallacy ;-)

Anyway, most members of this board deal with digital video, including acquisition, editing, distribution and demonstration, so I think that no one cares that analog NTSC is interlaced by definition.

One can master a progressive-scan DVD with 24 fps, 30 fps, not sure about 60 fps. One can master a high-def DVD with 24, 30 or 60 fps. So, we have progressive disk and progressive TV, now the only issue is transmission. Cheaper and older digital TVs do not accept 1080p, though they accept 1080i, 720p and 480p. They usually accept either 60i or 60p, but not 24p or 30p. Older analog TVs do not even accept 480p. Therefore intelaced signal was (and still is) the least common denominator, and DVD players know how to interlace progressive signal.

Now back to original question. 30p will work if a player can output 30p and a TV can accept it, or if the player can telecine it in 2:2 cadence and the TV can decode 2:2 cadence. Not many TVs and DVD players are capable of proper dealing with 2:2 cadence. AFAIK, many TV shows are shot and mastered in 30p.

If video is encoded in 24p, then the player can output it as it is, provided that the TV can accept 24p (Pioneers, some Hitachis, other hi-end TVs). Also, some Pioneers are capable of 72Hz refresh rate, so you will have 3:3 frame sequence with less judder. Another choice is to telecine 24p into 60i, DVD players know how to do that. If a TV is capable of reverse telecine as many modern TVs do, than you get proper 24p back on your TV with no loss of resolution.

Also, you can encode a DVD as 24p-in-60i (telecined), this way the player would not have to telecine it, and the TV would have to decode 3:2 cadence. An analog TV would not have to decode anything.

All in all, 3:2 cadence support among players and TV sets is better than 2:2 cadence support, and many older TVs do not accept 24p. Therefore 24p-telecined-into-60i is the most compatible format for today. Considering that DVD players can telecine in runtime, why not distribute in real 24p?

[Alex Humphrey]

Well two months later: numerous tests that even bored myself. I can't see any reason to use 30p for anything other than HD broadcast. Since I do SD DVD's from 720p HDV and going to go i-tunes HD.. (720p at 24fps max) the 30p is academic. I wanted to rationalize shooting SD widescreen at 60i, and while the results were very good (better than I had expected having used Sony VX2100 and TRV-900's and never thought much of them except for their color and low light capabilities) it still didn't compete to my eyes to a 24p source on DVD. So I went out to do some specific testing, burn a DVD with different tests, and force my friends (average consumers) to watch and give me their thoughts. Just because many of us can see the differences, can the average consumer? Would they notice or care? How much time difference is it from editing point?

The footage I shot was on my JVC HD110 in HDV 720p at 24fps 30fps and SD DV Widescreen anamorphic, to be encoded to DVD, shown at different aperatures/shutter speeds played on different brands of Progressive scan DVD players on 8 different plasmas and HD LCD's.. everyone (general consumer) handily said that the 720p 24fps at 1/48th to 1/60th looked the best, even for sports. The 30p didn't look bad, but since in NTSC DVD's are 60i and recognizes a 24p pull down neatly.. sending a reconstituted 24p from a 60i source (DVD's are 60i no matter what anyone says) and sends out through the HDMI cable, looks nearly as good as a store bough MGM movie. The 30p is broken into 60i and you have progressive scan and interlaced images hitting the LCD or plasma where they are then shown. every few frames there is a change as LCD/Plasma makes a progressive scan image out of an interlaced image combined with the two A/B progressive scan image. Little flexing and changing in image. To be honest I think the SD DV (wide mode) 60i that the JVC HD110 did converted to DVD looked great. It looked as good as any HDV 60i downconverted to DVD that I have seen recently, but the HDV 24p 1/48th or 1/60th looked better than anything else to my eyes and 8 other average consumers. I did a DVD with different chapters and forced them to watch it several times each to pick out what looked best to them and why. On a tube TV? No one can tell any difference... but who buys tube TVs anymore?

I took notes of exportation as well, (which I do not have in front of me, but I can post later if anyone is interested) that broke down the exportation time per minute of footage from each source. The numbers (from memory) were SD anamorphic 60 to DVD was about 1.5 minutes per minute of footage, 720p 24p to DVD was about 3.1 minutes per minute of footage and 720p 30p to DVD was around 3.5 minutes per minutes of footage... Edited and rendered out on a 24" imac Intel 2 Duo 1.8 with 3 gigs of memory.. Output in FCP using Compressor, Best 2 pass. Single pass was pretty good at less than half the time.

Now to stir things up for the 30p fans. I believe GHOST HUNTERS and a few other broadcast shows are shooting Pansonic DVX100's at 30p for the interviews, walk throughs etc.. then use the smaller panasonics with infrared shooting 60i in frame mode to better match the DVX100's 30p. Why 30p and not 24? I dunno.. might look better in broadcast, and they might not figure on DVD sales later.. or maybe they have a better DVD compressor program than Apple's Compressor, which is an OK compressor program, but doesn't thrill me for much, except 24p and 60i to DVD.

[Aaron Courtney]

Originally Posted by Alex Humphrey

On a tube TV? No one can tell any difference... but who buys tube TVs anymore?

LOL! I wish I could lend you my 200# Sony 34XBR970 and see what the results would be...

Thanks for adding your personal experience to this thread, Alex.

[Aric Mannion]

You can make a progressive SD DVD? What program do you burn them in? DVD Studio pro adds interlacing even if your video is progressive.

[Laurence Kingston]

FWIW, a lot of high budget episodic TV is actually shot on film at 30p. The show "Friends" is one of these. On DVD it is encoded as 60i according to the flags, but for all practical purposes, what you see when you watch it is 30p.

As far as whether or not it looks like film: well it is film and of course it looks like it. Why do they shoot 30p rather than 24P? Well nobody is ever going to watch "Friends" on film in a theater, and on TV it looks a little better: all the resolution and a little smoother motion.

You'd think that making PAL versions of shows like these would be impossible, but go to any British video store and you'll see these shows available in PAL with pretty smooth looking conversions.

By the way, I hate the show "Friends" but my wife is a fan.