Why 24P is Important from RED Centre Podcast
 

For those who don't understand the importance of 24P, and for a very in-depth discussion of its relevance in the 5D MKII (and a bit of a digression into the 5D's importance in the digital cinema world) head over to the RED Centre Podcast. The June 1st edition, Episode #36, about 9 minutes in, talks about the 5D Firmware Update and why 24P is important at about 15 minutes in.

RED Centre is a podcast put on by the crew at FX Phd., a training site/school for visual effects artists and deals specifically with the RED Digital Camera and more generally with digital cinema. It's worth subscribing to via iTunes... fascinating stuff for tech-heads.

RED Centre: fxguide - vfx knowledge

Mark, many thanks for posting that link. Those guys remind me of a former professor I had Personal page in acoustics -- he could make the most dry & complicated stuff both entertaining and understandable. Had to crack up when they said something like "But of course, it's only nuts who listen to this anyway." (Obviously, they know their audience ;^)

-- peer

Thanks Peer, it is nice being a nut...

It's a good explanation of why 24p is important for those planning to go to filmout, and why 30p is particularly ill suited for that purpose (or for converting to 24p) - but if that's not the plan (and it's probably not for most of the content shot on the 5D) I'm still not convinced of the absolute need for 24p.

30p IS NOT the news/reality/sports/video look that a lot of people seem to be making it out to be - 60i is (in the states at least). 30p is significantly closer to 24p than to 60i... it's a 25% increase in temporal resolution compared to a 250% increase! In terms of motion rendering I think the shutter speed has far more impact on the look than the difference between 24 & 30p - and now that we can control the shutter reliably I think it'll have a big impact on the look of stuff we see from the camera from here on out. I'd bet that most of the audience won't see the difference.

Edit: Also just wanted to say it's really worth listening to the rest of the podcast, the guest is really interesting, soldier/photographer/videographer talking about how the 5D is allowing them to shoot in low-light combat zones without having to use night vision cameras thanks to lenses like the 85mm 1.2.

Evan, it's not so much for the possibility of filmout that people are clamoring for 24P or 25P - it's for the problems that will come when a 30P project is ready for distribution to any PAL country - which is most of the world.

I'm dealing with this right now with our feature film, which was shot 24P, and distributed as such for the North American market, but every other territory we've dealt with is PAL. The conversion from 24P to 25P is not a huge headache, but is next to impossible when converting from 30P - at least with good results.

This is enough of a problem that it is keeping me from purchasing the 5D MKII or even using it on any project that has the possibility of any eventual distribution.

Of course, the 5D can be used for projects that will only see the internet, but that is extremely limiting... at least if you are trying to make a profit.

And then there's the web, where 24p takes less bandwidth than 30p. And specifically Vimeo, which throws away frames to achieve 24p.

Our older camera did 30p. We encoded 15p for the web, except for webisodes that had single frame gun flashes. If there wasn't much motion, 15p was fine.

Time consuming? Yes. Good results? Yes. Impossible? No.

Sofia's People: Canon 5dmk2 24p on Vimeo

Looks good to me.

Yes, of course it looks good to the naked eye, but a Quality Control Report on an HD-Cam PAL tape from a post-production house is LOOKING, often on a frame-by-frame basis, for problems such as ghosting, which are often the result of these kind of conversions.

It's not fun to be told that the tape you submitted to a distributor is not acceptable, after you have paid a post house over a $1,000 to produce the tape. And if your problem was caused by initial image acquisition in 30P, there is nothing you can do about it months later...

I don't want to instigate another tiring 24p "rant" thread, but other than the clean conversion to film, what is real advantage of 24p? Film has a certain color look to it, but that has nothing to do with frame rate. DOF has nothing to do with 24p, as evidenced by the 5D2. The only thing you get from 24p that is "filmic" is motion blur, because you have less frames per second.

Got it, that's what I was looking for - most people's justifications for needing 24p seem to just be 'film look', but international distribution issues make it a true, practical need. Well, let's hope Canon's really working on it.

Ghosting? I've seen ghosting in stuff that originated 24p and 25p. So is that footage unacceptable? Even if it started and ended up at the same exact frame rate? Seriously, if it looks good to the naked eye, then really, who's going to care? I doubt a post house would hold it's nose up in the air and refuse a paycheck based based solely on a few bits of ghosting?

A transfer to film requires an image sequence. 24 frames per second is still 24 frames per second no matter what the original frame rate was. If converted properly, if the cadence and timing is good, and if it looks good to the naked eye. What's the problem exactly?

Not trying to be argumentative, but I just not sure I see what the issue is. I could be wrong. It's just that your point seems a bit presumptive as to what the end result of a 30p-24p conversion would be.

In the past I admit it was rough going that route, but now it seems there are perfectly acceptable options for this.

The podcast is confusing. One minute these guys are discussing 30 frames per second and and the problems inherent in converting it, yet they relate it to interlaced fields. Huh? Last time I checked the 5D shoots 30p.

Maybe I'm missing something.

My point is that obviously you can deliver a fairly clean 24p project from 30p material. There are plenty of examples floating around the web. I'd bet money a post house isn't going to care that much if it's a clean conversion.

Ok, one last post and then I'll let it die.

Trust me. It matters.

The post house will still take the check, yes, of course. But when you distribute a film, you have to turn over a master to whoever is paying YOU. They, in turn, send your master to a post-production house or quality control firm, whose sole job is to go over the master with a fine-tooth comb, looking for flaws in both the video and audio. They are being paid by the distributor, say, Showtime, or ABC. They are covering their ass by finding flaws in the material. A 30P to 24P conversion can result in the kind of flaws that can lead them to rejecting your master.

That is very expensive.

But I'm sure you are aware of this; it simply bears repeating.

And look over the resumes of the guys who host the RED Centre Podcast. They know what they're talking about. Trust them.

For all the Europeans on this board and any future Aussie or European customers of mine, I hope for 25/24p. I will still be shooting with the 5D regardless but I hope even more firmware upgrades happen. I just won't be infuriated with Canon from now on since I think I'll be very pleased when I shoot with exposure control. Now that I'm happy with them more completely, I hope for their sake they get 25p working so they can sell more cameras.

Evan, you are not alone; this precise concern has been driving me absolutely insane for months now, what with the increased prevalence of video modes on still cameras of late. I was beginning to think I was the only one who thought about this.

The international compatibility issue I can completely understand. 24p can be converted to both NTSC and PAL rates without the headaches of the other potential cross-conversions, so it makes sense there. Combine that with the fact that the Blu-ray video standard only supports 24p and 60i, not to mention the concern for cost on film shoots, and the desire to shoot 24p makes perfect sense.

But, despite the many legitimate reasons you can come up with to support the 24p fever, the podcast hosts seem mostly concerned with the misconception Evan addresses in his post: confusing 30p with 60i. They say "thirty frames" when they should be discussing "sixty fields". The example they give, where audiences can tell commercials from movies, is not because the commercials were shot at thirty frames per second, but because they were shot at sixty fields per second.

One could technically say that they were shot at thirty frames per second, but in the context of interlaced video "frame" has a different meaning, and it's only a logical unit of information that itself we never get to see. Each of those frames contains two separate images which, though stored together, were captured, and are ultimately played back, one after the other, giving us sixty distinct points in time represented per second, in stark opposition to both 24 frame per second film and 30p video.

The video look that we (at least in the NTSC world) are conditioned to see as "home movies" instead of "cinema" does not come from a measly six additional images per second. It comes from the almost thirty-six extra samples of time you get when you shoot interlaced material in our parts of the world. It's two and a half times the motion sampling that stands out, not a paltry quarter-again addition.

Those more experienced individuals out there can more than likely spot the difference between 24 and 30 frames per second, if they're paying attention, but a real, honest-to-God thirty frames per second is not the plainly obvious smack in the face that makes even the least trained home viewer say "this doesn't look cinematic", and speaking purely for the look of the footage, doesn't make a significant difference.

This is a great discussion but I'm voting two thumbs down on the podcast, it's filed with mindless chatter about stolen Red cameras and a lot of yourtaxdollaratwork GI Joe combat stories about winning the Silver Star etc. I didn't make it to the end, I couldn't take it. I caught about 90 seconds midway that had some interesting info re 24p but it's a lot of noise other than that.

The OP has a lot of good insight, I hope he revisits his thread. The podcast? ctl alt del.

Your reasoning reminds me a bit of the early 1990s when some (so-called professionals) were perplexed that we started developing tools for 24bit/96kHz audio, since, according to them, "no one can possibly hear the difference between it and the established 16/48 standard".

Hence, I would hope an issue like "30p to 24p" would have gotten a little bit more "scientific" attention than just trusting ones "naked eye" and relying on "examples floating around the web" as measurements.

So again, I thoroughly appreciated the RED guys podcast discussion that Mark pointed us to.

-- peer

Yeah, but who delivers in 24/96? The analogy doesn't really apply, if it did the HD Audio market would be a giant cash cow right now. When was the last time you purchased an HDCD? Plenty of people have shot on MiniDV and achieved theatrical distribution. Digital intermediates have been 2k, well below the standard resolution of film.

Whatever. I get that you're trying to vaguely insult me by insinuating I may not be a professional, but that's boring and pointless so let's get to the real issue...

I do appreciate Mark posting the link, I appreciate the discussion it has produced. I just don't appreciate the podcast itself. In regards to the 5D it borders on ignorant. They don't know what they are talking about. If were going to talk about the "science" of it, then they should very well know the difference between 30p and 60i. Unfortunately the speakers in the podcast didn't apply an REAL "scientific attention". Just assumption and guess work.

Really, the podcast seems a little fishy to me anyway. How could they not know that the 5D shoots in 30p and not 60i? Because of that, how can they possibly know what a 30p to 24p conversion will result in?

Unless... unless... they've never actually used the camera and converted the footage!!!
Because that's exactly what it sounds like. So tell me why I (or anybody else for that matter) should care what their (obviously biased) opinion is on a camera they apparently haven't used or done any actual tests with?

After all this is a forum thread for the 5D and not the RED camera is it not?

I'd even go as far to say that my opinion on the subject is more "scientific" than theirs simply because I have actually shot with a 5D and converted it to 24p with excellent results. Unlike the "so-called professionals" in the podcast.

You see, the scientific method requires that one must actually TEST a hypothesis, instead of blathering on about what the outcome MIGHT be.

I just want to mention a few quick points.

Firstly, I just want to state my enthusiasm for the Red Centre podcast because this thread is descending into a bit of an RC-bashing session. I've been listening to RC since episode #1 and I think they guys do an awesome job. It is probably one of my favourite podcasts and I've learnt a lot from it. Yes, they do have quite a chatty style but I like that.

Regarding converting 30p to 24p... here's a frame grab provided by Stu Maschwitz when he converted a 5DmkII video from 30p to 24p using Compressor (which uses motion compensation):

Even on a simple shot, the Cinema Tools/Compressor 24p conver... on Twitpic

It's definitely worth reading what Stu has to say about 30-to-24p conversions on his Twitter stream around the 31st May:

Stu Maschwitz (5tu) on Twitter

The key quote is "It boils down to: I don't think every frame of your movie should be a computer's guess at what happened between frames you shot."

24p + 180 degree = 1/48th. It is possible to have an 1/48th exposure for a 30fps frame rate, to get the "film look". The only problem is down converting to 24/25fps. Anyway, "film look" is not 24p. The film look is the man behind the camera. 2c

It's always interesting to me how the 24p hating never stops. When I got one of the first DVX100's in the US and helped started the DVX100 forum here, it was really a firestorm of "strobing" "pulldown" with lots of people arguing the 30p mode of the DVX100 was the real one people would use.

Of course, they were wrong and the many 24fps video cameras that followed prove that point even stronger.

I also happen to be an expert at frame rate conversions in Twixtor due to my work with still image motion and I've taking 5D Mkii raw files and Twixtored them. You can create okay 24p & 25p footage from 30p but slower shutter speeds (more filmic shutter) can create ghosting problems and higher shutter speeds can create artifacts. I posted one sample here somewhere.

Is it doable? Yes. But you will have long renders that will alter your master and requiring two steps for any changes after conversion.

24p is best mastering format for narrative work - that is not an arguable point. It can be argued that is the best mastering format for most work although 50p and 60p have their place in the discussion. This is because:

1 - 24fps guarantees access to theatrical exhibition worldwide. And given the huge library of narrative works all at 24fps, it will always be a standard for centuries.
2 - 24fps can easily be converted to 25p, 50p, 60i, 60p and even 120p without ghosting, artifacts and the like
3 - 24fps makes better web, better DVD, better blu-ray, better digital downloads and better d-cinema because it's simply less frames to compress and process, saving time, space and money

Those are facts - the realities of 24p. However, 50p and 60p render better motion for live events and sports as well as some news and journalism and are often a better choice (though NFL films and many others did fine shooting film).

And beyond fact, I've participated in our cities 48 Hour film festival for 5 years and see footage from any camera and framerate combo you can think of. A 60i film (and we have some very sharply done ones by seasoned pro) has never won. the 24p films have won every year, both audience and judges awards.

So unless someone has a really convincing argument that distributors, post houses and audiences prefer 30p, the 5D Mkii needs to add it (and you figure will add it, hopefully as a firmware update, not as a 5D Mkiii)

There are a few ways to approach the "make 30p look like 24p film" challenge:

1) Shoot at 1/60th. Slow the footage down. The result is perfect 24p with 180 degree shutter, albeit in slight slow motion.

2) Shoot at 1/48th (well, 1/50). This might be the right solution for dropping frames to hit 24p. (Can you say Vimeo?) 1/48th is a bit long, but by the time you drop six frames a second, it's an average of 180 degrees (smear, smear, smear, smear, jump...)

3) Shoot at 1/80. I like this (in theory) when playing back in 30p. Why? The gap between the exposures is 1/48th. The 1/80th exposure time is a bit stuttery, but this helps balance the extra smoothness that we get with 30fps vs. 24 fps. It's possible that this is also the best rate for conversions to 24p - too much smear makes conversions difficult. The sharper frames can be easier to convert - in theory.

But like Tony said above, test the theory. This is a subjective area, so try some test shoots yourself. If they all look the same to you, I'd choose 1/60 as your default. Maybe you prefer the smoothness of 1/50 or the slight stutter of 1/80.

Another factor is lighting. Do you get strobing at 1/60 and 1/80? Then definitely shoot at 1/50. One thing for sure, strobing lights are not part of the "film look".

But in the end, this is all hoop jumping. If/when Canon gives us 24/25p, we can get back to the business of telling stories with moving pictures.

I don't understand why anyone thinks 24p is being attacked. Maybe it's in the podcast but the only thing I've seen attacked in this thread is 30p. I think no one would complain if the 5d had 24p. But to say you can't shoot and distribute a movie based on one format is rediculous, yes 24 may be more mainstream but that doesn't mean there isn't an option for a good movie to get distribution if it's shot in a different format.

And what about 30p? I'm not 'hating' on 24p, that's generally what I shoot on my XHA1, I'm just getting tired of the 30p 'hating' that I see so much in discussions of the 5D.

My original argument was simply that 30p is much, much closer to 24p, visually, than to 60i - so if your goal is to get a 'film look' rather than 'video look' I personally feel 30p with the right shutter speed is close enough that most audiences (i.e. people who don't read this forum) won't notice the difference, whereas they can generally tell the difference if something is shot at 60i.

As for the podcast I don't think the hosts were confused at all about the 5D's format - the discussion of 60i had to do with the fact that conversion from 30p to 25p is significantly more difficult than either a 24p or 60i source - and for either international shooters or those seeking traditional (non-internet) international distribution that seems to me the best argument for needing 24p rather than just 30p.

I tend to agree that a lot of folks (not everyone mind you) think that 30p = 60i, and nothing could be farther from the truth.

HDCD..? The 24bit/96kHz that I referred to were systems we worked on for signal processing in post.

I can assure you, both Mike and Jason know very well the difference between 30p and 60i, and they know quite a bit more than that too.

This is disingenuous. But since I know Jason will reply to this thread shortly, I'll let him lecture you.

-- peer

Well for distribution you can always export to 60i, that works for most TV programing so thats a non issue.

Also bottom line is if your stuff is good, doesn't matter what frame rate it is, big deal distributers will still take it. Anyone ever watch the Blair Witch Project?

So if the amount of information a file/format carries is the most important aspect of production and post production, then why are we not all shooting and doing post in 60p? By your rationale 30p is a superior format because it carries more information than 24p. I'm still trying to figure out how exactly your analogy applies to this forum topic and frame rate conversion in general.


Maybe they do... maybe they don't. I was speaking strictly about the statements made in their podcast. Specifically, the difficulties in converting 30p files from the 5D to 24p. In said podcast, they related some of the problems to fields. There are NO fields in 30p. It's just that simple.

Maybe they were saying fields when they meant frames. I'll have to listen to the podcast again to be sure, but I recall them relating some of the problems to fields that result in stair stepping.

I don't listen to their podcasts. Maybe they are the podcast video rock stars you make them out to be. I'm sure they are very knowledgeable guys. I'll even assume that 99% of the time they are spot on.

This time? No so much.


No more disingenuous than than stating a known 30p camera shoots in 60i. Obviously the 5D is stealing a little thunder from RED. The fact that they obviously have a bias in regards to the RED camera makes this "fields" faux pas more suspect.

Lastly... I must give you kudos for your last comment. It was hilarious! Your sycophantic adoration is a little... uhhh, weird, but it was funny none the less. I haven't laughed like that in quite some time. It's amusing to know that lil' Peer is waiting around for big daddy to come give me a stern talking to. LOL!

True. Very True.

Actually, if it was possible to get, say, 96000 frames per second (as we do in sound) this would indeed be better -- the higher the sampling rate, the more interpolation possibilities. But as of yet, the sampling rates of audio vs video aren't even in the same ballpark.

That's fine, I'll try help you out by rehashing this one more time:
You stated that "if it looks good to the naked eye" there shouldn't be any "problem" and that "there are plenty of examples floating around the web" to prove this point.

To this I replied that this measurement -- "if it looks good to the naked eye" -- didn't sound very scientific to me, and that it reminded me of some people who said exactly the same thing to us ("if it sounds good to the naked ear") when we were developing 24bit/96kHz audio tools early in the 90's.

You see, some of us are so anal that we use oscilloscopes, spectrograms, and even raw bit-stream printouts to determine "if it sounds good enough". Hence, if my field of work had been in video, I doubt I would rely on your "if it looks good to the naked eye" or use those "plenty of examples floating around the web" as my measuring tool.

-- peer

The problem is that the numbers never tell the full story -- at least the way they're thrown around in these forums, ultimately the naked eye is the final arbiter.

When it comes to this kind of work, "the naked eye" is trivial, as in; everyone has one. To satisfy peoples "naked eyes", science and engineering rely on more sophisticated tools (in conjunction with the eyes).

-- peer

...and yet nobody shooting video seems to be doing this and nor do they seem to want to.


So, confusing 60i with 30p sounds scientific to you?

24p is still 24p no matter what format it originated on. If it looks good on a frame by frame examination. Then yes it is "good enough" for me and for a post house. I'm not saying it is without some minor flaws, but the benefits of shooting with this camera far eclipse the rare minor flaw in the conversion process.

Here's the inescapable fact Peer. Plenty of projects with less than stellar format acquisition and delivery have made it past these supposed post facility standards, but have also ended up on TV and in theaters. Stuff with FAR less quality than what is shot on a 5D.

I've shot on a 5D. I've converted and delivered the end result in 24p, to more than happy clients, and for my own personal projects. To reiterate, it sounds as if the people on the podcast never took the time to do the same thing. Me and many other people have done this exact workflow with great results. Have you? Have the guys on the podcast done so? The answer seems to be a resounding NO. Yet, here you are carping on about scientific process from a position of ignorance. There's that pesky part of the scientific method, yet again rearing it's ugly head. TESTING!

If I took the time to worry about the minute level of anal nitpicking you ascribe as important. I would never get any projects off the ground, and neither would a lot of other people on these boards.

Bruce Springsteen recorded "Nebraska" on a Tascam 4-Track cassette recorder. It is a masterpiece. That album sounds "good enough" to me.

Hey Tony, I think you may actually need to listen to the podcast again. I finally did after all of the discussion here. When they were talking about fields they refferring to the "old days" of getting a 24 frame look from 60i. Instead of it being a simple 3:2 pull down, they were saying that what actually happened was you would use part of the upper field of say frame 1 and the lower field of frame 2 in order to get a matched frame that was sharper. I don't think they meant that this is how the 5dm2 works.

The issue they seem to have is that in order to get that look of 24 it's actually really difficult, because if you throw away every 5th frame it looks more jittery then it should, to me this makes since.

They may in fact be shills for RED I don't know I don't listen to them (other then this podcast) I will say that it seems silly for anyone to propose that a theoretical camera (scarlet) is better then a camera you can shoot with today. Don't get me wrong the day that I can go down to my local rental house and pick up a scarlet and shoot a movie in 24p 3k or whatever yes, it will have the 5dm2 beat. But I think it's silly to have a discussion about a camera that doesn't exist (yet?) and one that does.

Also I don't understand what the controversy is, Is it really that earth shattering to think that a lof of people on a film making forum would want 24p? No of course not. And yes 30p does look more "TV" then 24p but it also looks more 24p then 60i.

Agreed, I even said as much in an earlier post. It seemed to me that the portion where they were talking about the 5D specifically, was the point at which they brought up fields.


For sure. I wasn't even in disagreement on this point. I would jump for joy if they released a 24p update to the 5D. My point has always been that you can deliver good 24p from stuff shot on a 5D.

24p acquisition is better, even preferred, but nowhere near as important as some people make it. A few years ago it might have been a bigger issue, but with the advances in hardware and software it isn't.

No one is "confusing" 30p with 60i. I suggest that you listen to the podcast again.

Well, this is pretty much what I expected -- you are confusing artistic abilities with engineering/scientific aptitudes. Yes, Springsteen managed to make his masterpiece using a subpar analog Tascam 4-channel cassette recorder, and Beethoven managed to write his 9th symphony while being completely deaf. However, none of this has anything to do with the issue at hand -- namely, "why 24p is important".

By the way, I know for a fact that the brilliant engineers at Tascam use both oscilloscopes and spectrograms (and even tools that I've helped developing). The "naked ear" isn't good enough for those guys either.

-- peer

Having produced an international BD from a variety of frame rates, I think 24/25p is still a huge issue. The quality generally suffers when making the conversion, and the better processes are slow. When working on deadline, the last thing I want to face is a framerate conversion. (I certainly don't plan to convert to 24p for this year's 48 hour film project.)

So, yeah, conversion is possible, but nothing about it is desirable.

Sorry if this comes off as argumentative. Clearly from your first sentence, you also prefer 24p acquisition. By implementing 24/25p, Canon can save us significant time and increase the end quality of our productions.

You can crunch numbers and measure everything you want, but film and video are ultimately sensual experiences. All the 0's and 1's in the universe will never get you over the finish line and tell you what makes a given piece of content compelling. Dismiss the eye, the ear and the heart at your peril my friend.

The best of all worlds is to consider the human experience as well as the numbers. If you can correlate the two, you can make good decisions.

For instance, I know not to buy an f/8 lens for low light work. I don't need to waste my time buying it to see how it feels. On the other hand, I might buy an f/1.4 lens that makes ugly pictures, in which case I'd want to sell it to get something better.

Numbers don't tell the whole story, but they can help keep us from going down a fruitless path.

That's right Jon. Under most circumstances, you need both, but Peer is dismissive of the eye, saying "When it comes to this kind of work, the naked eye is trivial."

I'd like to take the chance to try and clarify myself before the thread is finally locked, if that's all right:

I never meant to imply that they were flat out confusing the concepts of 'progressive' and 'interlaced' (nor did I mean to attack their credibility; this thread's taken a nasty turn that I certainly didn't anticipate), only that the impression I was left with after listening to the podcast--three times, just to see if I misunderstood them--was that they were associating twenty-four frames per second with a cinematic, filmic look, and thirty frames per second with the look of video. My point was simply that I think this association is unfair, as what most of us in NTSC countries have grown accustomed to as the silky-smooth, high sample rate motion of the "video look" is not thirty frames per second in the way most people think of the word "frame". Since it's interlaced, what we're all used to seeing is actually comprised of sixty individual images per second, not thirty; as such, an image capture rate that's a mere six samples per second more than twenty-four will not make your footage leap to the realm of TV commercials, the ten o'clock news, and amateur recordings of childrens' birthday parties. To do that, you'd need to instead record thirty-six more images per second than the twenty-four we're using as a base for comparison.

Put more simply, if I may take what Nick said a few posts back just a bit further, although 30p provides smoother motion than 24p, it's nowhere near enough to scream "video" to viewers.

That may be blindingly obvious to everyone, but no matter how many times I review the podcast I get the impression that the hosts are misstating the difference between the two framerates. I'm sorry if it seemed more inflammatory than that.

Along those lines, I have a theory (untested) that shooting and playing back 30p at 1/80 will have a similar effect as 24p at 1/48.

30p is a bit smoother than 24p. By increasing the shutter speed to 1/80 @30p, the gap (shutter closed time) is actually 1/48. This will give a bit more stutter to a 30p video to help compensate for 30p's inherent additional smoothness. We will also get about half the motion blur of 24p 1/48, which could be a good thing.

On the other hand, if you will slow 30p down to 24p, shoot at 1/60 for a perfect 180 degree look. And if you will drop frames to get down to 24p, shooting at 1/48 (1/50) is probably the right approach.

If you will use advanced processing to go from 30p to 24p - test it! 1/48 might be the most natural, but sometimes the conversion barfs on soft edges. In that case 1/60 or 1/80 might be best. It really depends on the conversion algorithm and your content.

The day that we can record audio and 24p (fingers crossed) will be blissful...