question about 24p and 60i

[guerillaEMPIRE]

Ok, heres my delima. I am going to shoot the holloween jam in austin on the 31st and I still don't quite understand the whole 60i and 24P thing. I want SOME slowmo shots, but I want to shoo the whole video in 24PA. I also know that I cant just switch to 60i, as it will be corrupt in some way and i cant risk that. However, i also dont want to be changing tapes all the time as i might miss something. Also, i get better light with 24p, correct? as i will be filming in the dark with minimal light as well and a little led light oncam. what should i do? shoot completely in 60i? and go through hell in post. or shoot in 24p and hope for the best?

 

[David Jimerson]

You don't have to change tapes to switch between 24p and 60i.

You need more light with 24p than with 60i.

If you're only going to shoot one frame rate, I'd do it in the frame rate you want the project to be. If 24p, no, the slo-mo won't be super-smooth, but it's better than shooting 60i and converting it all to 24p just because you might want a few shots in slo-mo.

 

[ryvac]

yeah, I always get confused with the 24p, 24pa and 60i frame rate thing in the DVX. it's always good to re-read the DVX book to refresh your memory!

well for your project, I'm not sure what kind of slow-mo tech you are going to use but I'd recomend you to shoot 24p.
if you want to shoot 60i footage then do so. mixing/editing 24p and 60i footage shouldn't be a problem.
mixing 24pa and 60i footage will be a problem....

 

[ihatedv]

Ok, heres my delima. I am going to shoot the holloween jam in austin on the 31st and I still don't quite understand the whole 60i and 24P thing. I want SOME slowmo shots, but I want to shoo the whole video in 24PA. I also know that I cant just switch to 60i, as it will be corrupt in some way and i cant risk that. However, i also dont want to be changing tapes all the time as i might miss something. Also, i get better light with 24p, correct? as i will be filming in the dark with minimal light as well and a little led light oncam. what should i do? shoot completely in 60i? and go through hell in post. or shoot in 24p and hope for the best?

I'd say shoot it all in 24p and just slow it down in post. Is your HW jam going to the big screen? If not than in the interest of keeping things simple shoot 24pa and call it a day.

My last shoot was done in 24pa, I slowed some shots down 50% in CS4 and it was money.

 

[David Jimerson]

mixing 24pa and 60i footage will be a problem....

Not when you use the 60i for slo-mo in a 24p project, which is what he wants to do.

 

[Cranky]

Not when you use the 60i for slo-mo in a 24p project, which is what he wants to do.

Mixing 24p-over-60i and 60i is ok too, but most players/TVs need about half a second to lock on cadence, so don't switch back and forth too often.

 

[David Jimerson]

Mixing 24p-over-60i and 60i is ok too, but most players/TVs need about half a second to lock on cadence, so don't switch back and forth too often.

He's referring to potential problems with using 24pA on a 60i timeline.

 

[andythefilmer]

From my experience, 24pA on a 60i timeline adds in noticeable scan lines in motion. I would just go for 24p normal and 60i for slow mo. I don't see a difference in 24p vs 24pA, though it is claimed 24pA looks more film like. I haven't tried slowing down 24p footage either.

 

[Cranky]

He's referring to potential problems with using 24pA on a 60i timeline.

Much fewer players understand 2:3:3:2 cadence compared to ubiquitous 2:3 cadence.

 

[David Jimerson]

Much fewer players understand 2:3:3:2 cadence compared to ubiquitous 2:3 cadence.

Has nothing to do with players; has to do with editing on the timeline and the extra stutter the 2:3:3:2 cadence can have when the file is played back as 60i. It doesn't have anything to do with synch; it has everything to do with the extra fields being arranged so that the second and third frames are on screen 50% longer than the others, and they're back-to-back.

No player "understands" 2:3:3:2 cadence, anway; it's not even a factor when making a DVD. In fact, no player would even read a pulldown cadence in an NTSC MPEG file ON a DVD; it would simply see it as straight NTSC and play it that way. So, if you took 24pA footage, didn't remove the pulldown, edited it as 60i, and then output a 60i file for a standard NTSC DVD, the DVD player wouldn't know it was 24p material. It would see only 60i. Yeah, you might see the stutter I described above, but you'll see that well before you ever get to the DVD stage. It's not because of the DVD player.

The only pulldown involved with a DVD player is if you feed it a 24p file (straight 23.976, not 24p with pulldown in a 60i stream) -- in that case, the file would carry 2:3 pulldown FLAGS to instruct the DVD player how to insert pulldown itself when playing out to an NTSC screen. But there's no actual pulldown in the file -- no extra fields to make it 60i. The player inserts those, and the only option for the flags is 2:3 pulldown.

 

[David Jimerson]

From my experience, 24pA on a 60i timeline adds in noticeable scan lines in motion. I would just go for 24p normal and 60i for slow mo.

You wouldn't do it that way for slo-mo, though. You'd do it on a 24p timeline, because slowing down 60i to 40% lines up each field with a frame on a 24p timeline, thus giving you the smoothest slo-mo with no blending of fields. So, for that, you shoot 24pA.

I don't see a difference in 24p vs 24pA, though it is claimed 24pA looks more film like.

People who don't know what they're talking about claim this. Both 24p standard and 24pA start out exactly the same way -- they're imaged at 23.976 fps. The difference comes when they're split into fields and arranged in a 60i stream.

Once you remove the pulldown and reconstruct the original 24p frames, they're exactly the same.

I haven't tried slowing down 24p footage either.

It doesn't work well because there are too few motion samples. There's too much of a difference in position betweem moving objects from frame to frame, so there's more of a "jump." When you slow it down, it's more pronounced.

 

[Cranky]

No player "understands" 2:3:3:2 cadence, anway

Not true. For example, this is HQV test, and obviously HQV's own products pass this test (their own site is down, so had to use this one):
http://www.audioholics.com/educatio...ing-for-dvds/hqv-benchmark-dvd-testing-part-1 My Blu-ray player has the HQV chip and passes 2:3:3:2 cadence test.

In fact, no player would even read a pulldown cadence in an NTSC MPEG file ON a DVD; it would simply see it as straight NTSC and play it that way. So, if you took 24pA footage, didn't remove the pulldown, edited it as 60i, and then output a 60i file for a standard NTSC DVD, the DVD player wouldn't know it was 24p material. It would see only 60i.

Not true again: http://www.hometheaterhifi.com/the-dvd-benchmark/177-dvd-benchmark-part-5-progressive-scan-dvd.html Bear in mind that this article was written 9 years ago, so almost all modern DVD players support 24p-in-60i detection, at least in the most common 2:3 form.

The only pulldown involved with a DVD player is if you feed it a 24p file (straight 23.976, not 24p with pulldown in a 60i stream) -- in that case, the file would carry 2:3 pulldown FLAGS to instruct the DVD player how to insert pulldown itself when playing out to an NTSC screen. But there's no actual pulldown in the file -- no extra fields to make it 60i. The player inserts those, and the only option for the flags is 2:3 pulldown.

AFAIK (I looked high and low for this, if you have better information, please quote your sources), DVD-video is always interlaced. The sequence can be marked as progressive, but it is field-based, not frame based. The difference between 24p DVDs and 60i DVDs is that former are marked as "progressive sequence" and have pulldown flags, which a player in theory must obey to produce 60i, but most of 24p-capable players ignore it and go straight to low-level 24p footage (actually, should be 24PsF footage) and output either 24p or 60p or 60i depending on player's and TV's capabilities and setup. Read more at http://www.hometheaterhifi.com for details.

EDIT: Heh, Silicon Optix has been acquired by IDT, I did not know this.

 

[David Jimerson]

Not true. For example, this is HQV test, and obviously HQV's own products pass this test (their own site is down, so had to use this one):
http://www.audioholics.com/educatio...ing-for-dvds/hqv-benchmark-dvd-testing-part-1 My Blu-ray player has the HQV chip and passes 2:3:3:2 cadence test.

I can't speak to the internal workings of a Blu-ray player and all its components; I wasn't referring to it. I was referring to standard DVDs.

Note, though, this passage from this link:

DVDs are recorded at 24 frames per second, just like the films from which they came. If a DVD player cannot correctly translate this to 30 or 60 frames per second (as needed) then the result is a significant potential for artifacting, in this case a moire pattern. Using a race track with highly-detailed and naturally highly-contrasted stands the goal is: the shorter the lock-on time, the better. The image should also remain detailed during the process.

The reason for the pulldown flags is so that the player CAN correctly translate the footage.

Not true again: http://www.hometheaterhifi.com/the-dvd-benchmark/177-dvd-benchmark-part-5-progressive-scan-dvd.html Bear in mind that this article was written 9 years ago, so almost all modern DVD players support 24p-in-60i detection, at least in the most common 2:3 form.

Ths article refers to what I was talking about -- it discusses the pulldown flags here:

3-2 Pulldown

As we explained above, when film is transferred to video, 24 frames per second of film must be converted to 60 fields per second of video. The way this is accomplished is to show the first frame of film for 3 fields, then show the second frame of film for 2 fields, then the third frame of film for 3 fields, and so forth. This sequence, or "cadence" of 3, 2, 3, 2, 3, 2 is what is called 3-2 pulldown. Sometimes this is written as 3/2 or 3:2, but this looks like a ratio, so we and most other video technicians prefer it written as "3-2" or "2-3." Both are correct, but we'll use the more popular "3-2." When a player or TV can detect the 3-2 pulldown encoding, this is called 3-2 pulldown detection, even though the advertisement for the TV might say that it has "3:2 Pulldown".

There are two extra flags available in MPEG-2 to make it easier to create a disc that has 3-2 pulldown. These two flags are called "repeat_first_field" and "top_field_first." A frame in the MPEG stream can have "repeat_first_field" set to "true," and that tells the decoder to generate 3 fields from this frame, rather than 2. The decoder plays the first field, then the second field, then the first field again, thereby making the 3-field section of the 3-2 pulldown cadence. The next frame would generally have "repeat_first_field" set to "false," so the decoder will generate 2 fields. Because fields have to alternate between even (bottom) and odd (top), the "top_field_first" flag tells the encoder which of the two fields in the frame should be sent out first. The "top" field is the odd numbered scan lines: 1, 3, 5…, while the "bottom" field is the even numbered scan lines: 2, 4, 6… If the top field is first on a 3-field frame, the decoder will output top, bottom, top. The next field needs to be a bottom field, so the next frame will have top_field_first set to "false."

It's referring to the flags embedded in an MPEG file. These are not actual fields or segmented frames; they're just instructions.

The article does go on to describe snatching the 24p frames BACK OUT of the 60i stream created using the pulldown flags, but that's not the same as detecting 24p pulldown within a 60i file as it exists on the disc.

AFAIK (I looked high and low for this, if you have better information, please quote your sources), DVD-video is always interlaced. The sequence can be marked as progressive, but it is field-based, not frame based.

OK, here are the file properties of a VOB file on our HVX BootCamp DVD, which is a 24p DVD:

Note that it's a straight-up 23.976 progressive file, and it's on a commercially-replicated DVD. This reading is straight from the DVD.

This is advantageous because it takes up less space than a 60i file would, leaving you more room for a higher bitrate, a more robust sound track, or more extras.

The difference between 24p DVDs and 60i DVDs is that former are marked as "progressive sequence" and have pulldown flags, which a player in theory must obey to produce 60i

No, the difference is that the files are actually, on disc, as 24p or as 60i -- and any disc can actually carry both; you're not stuck with only one or the other. This is fairly common on commercial DVDs where the movie portion is 24p and the extras are 60i.

but most of 24p-capable players

Any DVD player is capable of playing a 24p DVD.

ignore it and go straight to low-level 24p footage

It can't ignore the flags; it's all it has to go by.


In any case, this is all really, really beside the point in this thread; this is about slo-mo and tangentially about editing 24pA footage on a 60i timeline. It doesn't actually have anything to do with DVD.