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Old August 14th, 2007, 09:31 PM   #1
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Framerate Confusion

Can some of you experts explain the various different framerates that flod around..

Specificly the difference between 24P and 24F and 1080i vs 720p

The confusion arises when I read about the HVX200 specs and it goes all way to 60p 720, where the XL H1 only has 1080 60i 30F 24F. Does that mean you cannot shoot slowmotion footage with the H1 in 60 frames progressive?

In my understanding the 1080 and the 720 HD formats cant be compared and are two different standards? Where the 1080 standard is specificly for interlaced broadcast, and 720 is for progressive? Therefore its confusing to find that there are 24F modes in 1080.

To make it more understandable. Say I want progressive scan, with the option to shoot slowmotion footage in some instances. Would the XL H1 be able to do the job? (either pre or post production)

PS: Im using the Pal system, so take that into account.

Last edited by Nik Skjoth; August 15th, 2007 at 04:09 AM.
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Old August 15th, 2007, 03:07 PM   #2
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Originally Posted by Nik Skjoth View Post
Can some of you experts explain the various different framerates that flod around..

Specificly the difference between 24P and 24F and 1080i vs 720p

The confusion arises when I read about the HVX200 specs and it goes all way to 60p 720, where the XL H1 only has 1080 60i 30F 24F. Does that mean you cannot shoot slowmotion footage with the H1 in 60 frames progressive?

In my understanding the 1080 and the 720 HD formats cant be compared and are two different standards? Where the 1080 standard is specificly for interlaced broadcast, and 720 is for progressive? Therefore its confusing to find that there are 24F modes in 1080.

To make it more understandable. Say I want progressive scan, with the option to shoot slowmotion footage in some instances. Would the XL H1 be able to do the job? (either pre or post production)

PS: Im using the Pal system, so take that into account.
I'm no expert, but I'll take a stab.

1080 is now available in a progressive mode. My Canon HV20 can shoot 1080 24p. Canon's 24f mode is a bit different. It uses an interlaced sensor to create a very close progressive look. Many people on this forum can't tell the difference.

As far as slow motion, there is a work around for turning 60i footage into 60p. Here is a thread explaining it: http://dvinfo.net/conf/showthread.ph...ht=slow+motion

You loose a bit of vertical resolution, but I think it looks better than 720 60p footage, which is the only resolution you can get true 60p footage from. Hope this is a good start.

Thomas
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Old August 15th, 2007, 11:33 PM   #3
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Thanks. That link was a gem..

So you are saying that the XL H1 is the better choice over HVX200.
Or rather... 1080i is better than 720p?
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Old August 16th, 2007, 01:42 AM   #4
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You loose a bit of vertical resolution, but I think it looks better than 720 60p footage, which is the only resolution you can get true 60p footage from.
Thomas
Not a chance. You loose half your vertical resolution. Yes this is a good work around for those who have interlaced cams, but there is a reason why 60p is a sought after feature with a cost premium.
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Old August 16th, 2007, 03:53 PM   #5
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So you are saying that the XL H1 is the better choice over HVX200.
Or rather... 1080i is better than 720p?
I think you should base your decision on work flow. I don't have the money for a flash-based system like the HVX200. Storage on tape rather than hard drive is much more cost-effective for me.
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Old August 16th, 2007, 08:00 PM   #6
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1- Interlace versus progressive: Obviously, some formats are interlaced and some are progressive.

For interlaced formats, 1 frame = 2 fields. 59.97 fields per second is sometimes referred to as "60i" and other times 29.97fps (frames per second) interlaced.

Progressive Segmented Frame: This refers to progressive frames sent down an interlaced system. The frame is split up into two fields, and each field is sent in sequence. This makes a difference for CRT display... if you displayed picture 24 times a second, you would see flicker. But by flashing picture twice- at 48 times a second- you see a lot less flicker.

If material is compressed, the codec may have different modes for interlaced and for progressive footage.

2- Frame Rates (complete frames, not fields):
23.98 (also known as 23.976; really 24 * 1000 / 1001)
24.00 <-- film
25.00
29.97 (really 30 * 1000 / 1001)
50.00
59.97

The most common frame rates are 25.00 (PAL broadcasting countries) and 29.97 (NTSC broadcasting countries).

If you have film at 24.00fps and want to broadcast it in PAL, then it is played back faster to fill 25.000fps (the audio is changed according, but with pitch shifting since the speedup is audible).

In NTSC countries... film is run at 23.98fps (either shoot at 23.98, or shoot at 24.00fps and play it back faster/slower accordingly). To put a 23.98 signal over a 29.97 interface (e.g. SDI, DV/firewire) or onto a 29.97 format, 3:2 pulldown is added to the signal. Every other frame has one of its fields doubled.
There is also the advanced pulldown scheme (AKA 2:3:3:2), which has compression advantages if the pulldown is removed to convert it back to 23.98. However, not all editing systems support advanced pulldown removal (particularly high-end systems).

23.98 signals can also be sent without pulldown over certain interfaces.

50.00 and 59.97 frames per seconds are framerates for some of the emerging HD formats (production and broadcasting).

2b- The odd frame rates are due to NTSC color broadcasting. The frame rate was changed to ensure better compatibility with black and white receivers. Usually in conversation, the .97 is rounded up. "30" and "24" usually mean 29.97 and 23.98 (or 30 * 1000 / 1001 and 24 * 1000 / 1001).

2- 1080i versus 720p
In PAL countries, these probably refer to 1080i50 (1080 active picture lines vertically; 50 fields per second) and 720p50 (720 active picture lines vertically; 50 progressive frames per second).
In NTSC, it would be 1080i59.97 and 720p59.97.

Future broadcasting systems will likely go 1080p50 and 1080p59.97.

These are common formats for HD broadcasting. However, other formats are possible for production... 1080p23.98, 1080p25, 1080p50, etc. etc.
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Old August 17th, 2007, 02:42 PM   #7
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Originally Posted by Thomas Barthle Jr. View Post
I think you should base your decision on work flow. I don't have the money for a flash-based system like the HVX200. Storage on tape rather than hard drive is much more cost-effective for me.
The JVC HD200 is very cost competative with the Canon XLH1 and offers the same work flow.
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Old August 18th, 2007, 06:37 AM   #8
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2b- The odd frame rates are due to NTSC color broadcasting. The frame rate was changed to ensure better compatibility with black and white receivers.
Not quite - the line frequency is 525x the frame rate, and the subcarrier frequency has to be an exact multiple of this to reduce patterning on monochrome sets. The problem that surfaced in the early days was that when locked to 60Hz this subcarrier frequency then interfered with the sound subcarrier within some sets. Moving the sound subcarrier frequency would have rendered all existing sets useless, hence the colour subcarrier frequency had to be moved - and since it and field rate MUST be locked together the frame rate then became 29.97.

The problems didn't start until timecode came along much later. With 50Hz systems (ie PAL) the seconds update every 25 frames and that's fine. Do the same approach with NTSC, update seconds every 30 frames, and timecode becomes like a slow running clock relative to real time. Hence the concept of drop frame timecode - a bodge to get the timecode to indicate real time, and mercifully something we don't have to suffer in PAL land.

The relevance to today is that come HD and the problem is still with us because of the neccessity to downconvert, and is why we still have the 24 and 23.98 dilemma. The problem there is less the slight difference of speeding up or slowing down to get from one to the other, but the effects on the timecode, and the more you think about it the more difficult it becomes. For cinema, exactly 24fps and ndf timecode is most logical, for "film for TV" 23.98 and df timecode is more pragmatic since the NTSC downconversion is then more straightforward.

The other thing I'd add to Glenns excellent summary is that the fundamental reason for psf coding is to enable progressive transmission over an interlaced transmission system - as long as 25Hz motion is acceptable. It's exactly like a telecined film over conventional TV systems. The choice is not then the simple 720p v 1080i as normally stated, but rather 720p/50 versus (1080i/25 AND/OR 1080psf/25). It's because of psf that most broadcasters in Europe at least seem to be going the 1080 route. If 1080 solely meant 1080i/25, 720p would be far more attractive.
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Old August 18th, 2007, 11:55 AM   #9
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If you shoot 24.00 or 23.98, you can only used NDF timecode. DF timecode is not defined for 23.98.

For 29.97, DF timecode drops 108 timecodes per hour. If a 23.98DF timecode system existed, it would have to drop 108 * 24 / 30... or 86.4... timecodes per hour. Such a system would be extremely bizarre I think. Anyways, you don't need it.

If you are shooting 23.98, you can shoot NDF and for most productions the relation to real/clock time is not important. There can however be a later inconvenience... broadcasters require 60i masters, and they will specify timings in 60i DF timecode. They also want a clean edit at that timecode... if something is cutting to black, the field(s) where the cut is should be black. Sometimes it is impossible to do this on your 24p master. When you add pulldown, some of the 29.97 frames are a mixture of 23.98 frames (one field from different 23.98 frames). So you can't get a clean edit that way. You need to go into your 60i master and insert frames to fix things up.

On the other hand... and in my opinion... this is a pain in the butt, but it is ok since it doesn't affect the final picture quality. Whereas something like the use of interlacing in HD broadcasting does do that.
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