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AVCHD Format Discussion
Inexpensive High Definition H.264 encoding to DVD, Hard Disc or SD Card.


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Old April 8th, 2008, 09:57 AM   #1
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60i vs 30p vs 24p

I hope I don't start a firestorm with this question, but since I'm still learning about this stuff, please be kind :)

I've searched and read about all of these shooting modes, but is there a "superior" choice among these 3? I know the true answer is "whatever you like", although I want to make sure I'm not confused about a couple of things...

Let's say I want to shoot something (like a trip) where I only have ONE chance to get the material. Is it better to shoot in 30p/60i and convert to 24p later, or does shooting 24p on the camera natively produce better results rather than conversion from 60i/30p? If it's simply less post production rendering, then I would likely want to shoot at a higher rate. That way I can do whatever I want with it later. The one I'm most confused about is 60i vs 30p. I have a Canon HF100 and realize that 30p is a new feature, but what does that really do for me when comparing to 60i? Again, I've tried to search articles for this on this site (and others) but haven't found a definitive answer. Please feel free to send links if you don't feel like explaining all of the details. Thanks in advance for any help!
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Old April 8th, 2008, 11:40 AM   #2
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In my opinion the only reason to shoot 24p is if you want to transfer to film for distribution in a theatre or to a film festival. In this case it makes transfer to film at 24fps easier. Since 24p is the slowest frame rate it has the most motion artifacts or judder which is poor for any fast movement or especially movement across the screen. Video shot at 24p needs to use film shooting techniques NOT video approaches( pans, fast zoom and large depth of field are not good for 24p). An inexperienced user shooting at 24p will produce video that is likely to have juddering images that will border on unwatchable video. The fastest frame rate and thus the smoothest video will be from 60i. For viewing on a CRT 60i will be the best for all instances. 30P has advantages for PC viewing and reducing frame to 15P for internet use. IT still has half the frame rate of 60i so will not be as smooth but a little better than 24p. The smoothest video with high resolution will be 720P60 used by the sports networks to give both high definition and smooth motion. For a consumer shooting their holidys or family video stay with 60i or 720P60. IF you want to have that film look use film techniques for shot composition and exposure of the scene but in my mind there is no need to have the judder frame motion of film of 100 years ago.
You can tell I am not a fan of 24p!!!!

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Old April 9th, 2008, 01:17 AM   #3
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Aren't the colors and the whole look different when shooting progressive?

I am trying to evaluate how much 30p would be worth to me.
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Old April 9th, 2008, 05:45 AM   #4
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Originally Posted by Sean James View Post
Aren't the colors and the whole look different when shooting progressive?

I am trying to evaluate how much 30p would be worth to me.
according to canon:

http://www.usa.canon.com/consumer/co...delFeaturesAct

24p Cinema Mode
spacer

24p Cinema Mode enables all aspiring moviemakers to achieve a professional "film-look." You can change the camcorder's frame capture rate to 24p (recorded at 60i), which provides the appearance of the same frame rate as movie film. In addition, you can use the VIXIA HF10's CINEMA setting, which changes the color and tonal characteristics, evoking the look and feel of a movie shown in a theater. For added flexibility, these settings can be used together or independently.


30p Progressive Mode
spacer

This is a unique feature that only Canon offers in the consumer camcorder market. You would otherwise have to look to professional video cameras in order to have this sophisticated tool at your command. In addition to the standard interlaced video frame rate of 60i, you may choose to set the VIXIA HV30 to capture video in 30p which is (30 progressive frames) particularly useful for footage to be used on the Internet. In addition, this setting gives enhanced quality to still images captured after recording. Excellent for action shots and sports.
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Old April 9th, 2008, 06:55 AM   #5
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Frame rate is just that. How many frames are exposed in a period of time ( normally related to frames per second). The more frames the smoother the motion. Colour and exposure will be the same for the same relative exposure times controled by the gamma curves and colour matrix of the sensor. IF you don't change these elements they will be the same for all frame rates. There are of course other implications with depth of field due to iris changes. However with the same iris opening then these will be the same too. Remember what you are doing is taking many still photos one after the other and playing them back at a rate that fools our eyes/brain into thinking its fluid motion. Too few photos and our eyes/brain don't get fooled and view them as a fast slide show. More frames than about 50 per second and we start to think of the images as in motion. To get the so called "film" look consumer cams change the frame rate AND the colour characteristics of the sensor. Without these changes then a frame rate change to 24p or even 30p would just introduce frame judder, in my mine a defect!!! If you want the colour and exposure effects of film you can do this at 60i with the right manually controlled cameras.
The problem with 24p in video is that NTSC TV's refresh at 60hz. 24 doesn't divide into 60 evenly!!! So it is necessary to play with playback to get all the frames to line up in sync with 60hz. With newer LCD's that refresh at 120hz and some Plasmas that refresh at 72hz this is possible. In the cinema with film this doesn't happen. The film projector moves the film through the gate at 24fps and a shutter with normally 3 or more blades exposes the frame while it is stationary in the gate leading to a 72 fps flicker rate. A faster flicker rate than either TV's in North America or Europe. This doesn't stop frame judder of 24fps but it does solve the flicker rate issue with our eyes/brain. Shooting video at 24p for transfer to film to be shown on a film project makes perfect sense. Cheaper to shoot and edit etc. But to shoot 24p to show directly on TV to me just doesn't make any sense since it is a poor emulation of what would be seen from a film projector.
Mario I am not sure what you mean by tape being smoother. Do you mean smooth motion or smooth image edges? This has nothing to do with whether the recording medium is tape or HDD it has do do with frame rate and how the camera is setup for edge enhancement etc. Your approach of downloading to PC everyday is a good one and would allow you to even look at a pure flash based cam as well.


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Old April 9th, 2008, 09:48 AM   #6
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ok, most of this is making sense. i guess i'm still interested in the pros/cons of 60i vs 30p. is 30p just a "number thing" that makes the HD cam sound good, but not used much in normal shoots? for instance, i'm planning to shoot an upcoming safari and want to make sure i'm using the best mode available. should i be taking advantage of 30p, or is 60i "to the eyes" a better mode?
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Old April 9th, 2008, 10:39 AM   #7
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Stephen I assume animals will be moving? Fast in uncontrollable directions? So there will be subject and camera movement if you are going to pan to follow( really bad idea for 24p,lots of judder)? 60i will have twice the effective frame rate. Watched on a normal TV 60i will be smoother motion than 30p( it has twice the number of images to capture movement of subject and/or camera even if those are effectively half the vertical resolution since they are fields captures rather than full frames). IF you want really smooth motion in HD then you should look at 720P60 cameras.
30p makes the software task of creating 15p video for the WEB easier though this is hardly a great challenge from 60i!!!!.
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Old April 9th, 2008, 11:15 AM   #8
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Hey Stephen,

Regarding 60i vs. 30P, you're still only getting 30 frames per second with either mode. The difference is with 60i, you're capturing two fields (odd scan lines then even scan lines) separated by either 1/60 or 1/50 (PAL) which must then be recombined to form a complete frame (de-interlaced) in order for a progressive display to correctly present the video. With 30P, you're capturing a complete frame (just like with a still film camera) from the same instance in time - notwithstanding any rolling shutter vs. ccd technicalities.

When we were all watching interlaced television sets, 60i was the obvious choice because that's how the displays inherently functioned. Obviously, the consumer electronics world has shifted gears and everyone is buying progressive sets. I think it was a couple of years ago that progressive sets outsold interlaced displays for the first time. And there's no going back either since the CRT has effectively been transplanted by PDP's, LCD's, and whatever else will be coming down the pike. So it is safe to say that we are now living in a progressive world, not interlaced. Unfortunately, we are still dealing with this interlace mess - in broadcast television and video acquisition.

The reason I say it's a mess is because it is impossible for a progressive set to perfectly de-interlace an interlaced-acquired video source. This is straight from the video processing chipset manufacturers. Any way you cut it, you're losing resolution somewhere, regardless of whether you employ sophisticated motion-adaptive, pixel-adaptive, or whatever adaptive algorithm. It simply doesn't work, and that's exactly what Yves Faroudja said upon selling his company (one built entirely on the prospect of high end de-interlacing technology) to Genesis.

The ONLY way for a progressive display to perfectly de-interlace interlaced footage is if the footage was acquired while shooting progressively. In this instance, either the display or the video playback device merely needs to employ a simple weave de-interlace algorithm to recombine the two fields into their original progressive frame because the entire frame was captured at the same instance in time - meaning there is no interframe movement (between fields). The problem, as many professional testers are discovering, is that with these advanced motion-adaptive de-interlacing video processing chipsets used today, most of them have proven to be incapable of detecting lack of interframe movement in interlace flagged video, so they screw up the de-interlacing of 30P video.

Apparently, this would not have been an issue with HD-DVD because the spec fully supported 1080/30P whereas BD does not - only supports 1080/24P and 1080/60I. So even if you are able to encode your BD at 1080/30P, you still have to flag it as 1080/60I and you're then at the mercy of the playback chain to ignore the flags and instead determine no interframe movement and correctly weave your interlaced stream and then frame double to get to 60 Hz.

So in a nutshell, native 24P video will be handled correctly with some displays (3:3, 4:4, 5:5) while others will have to use 3:2 pulldown (not ideal from a perfectionist POV), 30P - total crapshoot as it stands today, 60i handled universally but will never be perfectly displayed on progressive sets.
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Old April 9th, 2008, 11:16 AM   #9
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thanks for the info everyone. i think most definitely i will be using 60i to capture on my trip. since i just bought the hf100, i'll have to wait a while before i venture into the 60p HD market :)
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Old April 9th, 2008, 04:05 PM   #10
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Aaron you raise an interesting fact about progressive displays. Unless they are given a compatible input they have a likelihood of not being as smooth a display as CRT's to our eyes. As you say inputs that are driven to 30p, repeated twice, to get the 60hz refresh have a chance of displaying judder. CRT's have the advantage of displaying movement between fields emulating a 60fps image to our eyes for a 60i input. Although I have mainly Sony equipment I really feel that 720p60 would have been a better system to move to for everyone until we have the capability to get to 1080p60. I am getting more disappointed with cable TV as the judder/stutter is getting worse on most programs, don't know where the issue is but even occurs on my CRT's so isn't just my 1080p Plasma.
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Old April 9th, 2008, 04:37 PM   #11
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Originally Posted by Brian Smith View Post
according to canon:

http://www.usa.canon.com/consumer/co...delFeaturesAct

24p Cinema Mode
spacer

24p Cinema Mode enables all aspiring moviemakers to achieve a professional "film-look." You can change the camcorder's frame capture rate to 24p (recorded at 60i), which provides the appearance of the same frame rate as movie film. In addition, you can use the VIXIA HF10's CINEMA setting, which changes the color and tonal characteristics, evoking the look and feel of a movie shown in a theater. For added flexibility, these settings can be used together or independently.


30p Progressive Mode
spacer

This is a unique feature that only Canon offers in the consumer camcorder market. You would otherwise have to look to professional video cameras in order to have this sophisticated tool at your command. In addition to the standard interlaced video frame rate of 60i, you may choose to set the VIXIA HV30 to capture video in 30p which is (30 progressive frames) particularly useful for footage to be used on the Internet. In addition, this setting gives enhanced quality to still images captured after recording. Excellent for action shots and sports.
It sounds like the 24p mode would look the same as 60i, and the 24p cine mode would be with image adjustments I could also do on Final Cut pro.

The reason I am asking this: I owned a first generation DVX100, and 24p footage looked so much better than 60i, light/mood was represented better, and the colors were much nicer, so my impressions.

I wonder if these differences still apply, or if technology has advanced and made the image characteristics of interlaced, 24p pulldown, and 30p progressive identical?
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Old April 9th, 2008, 06:41 PM   #12
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It sounds like the 24p mode would look the same as 60i
I think this would depend on the television display. On TV's that can shift their refresh rate to 72Hz or 96Hz, do inverse pulldown, and display the 24P material as 3:3 or 4:4, the 24P material might look as good as or maybe even better than deinterlaced 60i depending on the material. But TV's that cannot do that will have to deinterlace the 60i which contains the pulled down 24P, and it won't look as good.
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Old April 9th, 2008, 07:23 PM   #13
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I think this would depend on the television display. On TV's that can shift their refresh rate to 72Hz or 96Hz, do inverse pulldown, and display the 24P material as 3:3 or 4:4, the 24P material might look as good as or maybe even better than deinterlaced 60i depending on the material. But TV's that cannot do that will have to deinterlace the 60i which contains the pulled down 24P, and it won't look as good.
I'm a bit confused here.

Don't get TV's just one kind of signal? Or, in case of a video clip coming from a Blue Ray disc, a signal in one particular compression format?

Why would they have to shift their refresh rate?

And regarding the pulldown, I didn't even know TVs do that. I thought this was just something that's done in the camera to create 24p while recording in 60i to tape.

OK, I'm a bit more than just a bit confused here.
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Old April 9th, 2008, 08:01 PM   #14
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Unfortunately TV's don't just get one type of signal. Depending on the TV they can deal with 480i,( really 480 60i, standard definition), 480p, 720P, 1080i, 1080p and the p can mean 30p or 60p. These over various interfaces from composite to HDMI. How the TV responds to these inputs may be different depending on the interface and certainly on the brand of TV. A lot of variants. This is made more complicated by what feeds the TV. DVD players can also decode what is on the disc depending on how they are set up for the TV they are connected to and its capabilities and represents a wonderful opportunity to have the DVD and TV set up in a non optimum fashion!!!! Sometimes the DVD has better decoding and sometimes the TV is better using particular interfaces will allow selection or not. For instance the new 120hz LCD would be better decoding the signal of 24p or 30p from a DVD rather than letting the DVD player do it and will create a smooth interpolated video image( create extra frames that are not in the original) that is likely smoother than the film judder of an actual film projector since it will interpolate images rather than just increase the flicker rate!!! . With HDMI the player and TV communicate and supposed to transmit data appropriate to the display capabilities.

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Old April 9th, 2008, 10:11 PM   #15
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Why would they have to shift their refresh rate?
It's not that they have to; it's a feature that is more commonly being implemented by the CE manufacturers. As was said earlier in this thread, you're not watching strict 24fps in a movie theater anymore - I don't know the exact history, but I'm sure someone does, LOL. I think most facilities employ frame doubling IIRC (so 48 fps) for a better visual experience.

Because 24fps is so embedded in feature films, CE manufacturers and video processing chipset manufacturers have taken it upon themselves to embed native support of 24fps in some equipment to elminate pulldown problems. So, with the right playback chain, you can view your BD movie in native 24fps glory where the player outputs 1080/24P and the display (preferably) frame triples, quadruples, or quintuples that stream to hit 72Hz, 96Hz, or 120Hz, thereby eliminating the 3:2 pulldown issue altogether. But the implementation is currently all over the map. Very few displays do this correctly at this point in time regardless of what the marketing material says - you can read the reviews, it's comical how some CE companies are handling this - total joke.
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