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Frame rate confusion.


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#1 Neal Bryant

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Posted 20 February 2009 - 02:03 AM

Hello everyone,

I'm DPing an ultra low feature and due to lack of money were are shooting on the XHA1 with a Redrock M2. Production has insisted that the footage shot every day is captured that night, but the only version of Final Cut we have on hand is Final Cut Express 4.

I am shooting in 1080i 24f, and I have done a lot of reading about the crazy Canon "F" modes, but I'm still a little confused. To add to my confusion, I can't find any info on what frame rate my sound mixer should be recording. He believes 29.97.

The only HDV option I have seen in this version of Final Cut is 1080i-60i. From what I understand, Final Cut will preserve the pulldown from the camera at that setting. If our post house (we don't have one yet) wants to remove the pulldown to edit in true 24p they should be able to, right? But if so, what should my sound man record his stuff at? 24p or 29.97? I would be in hot water if his sound discs can't be synced up with the video in post. :/

Thanks in advance for your help. We have just changed to this setup and I am starting to freak out.

-Neal
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#2 David Ghast

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Posted 20 February 2009 - 07:35 PM

I too would like to know what canon means by "F". Since your shooting 1080i 24f, i would assume they just use f as short for fps, as in your shooting 48i 1080, which is technically 24fps interlaced. If your shooting at 24fps, and i assume you plan on getting your film telecined, which means it will get a pulldown (unless otherwise requested), then you will be editing with 29.97i footage, so yes, your mixer should be recording at 29.97, or as they call it, NTSC dropframe. However if your editing at 24fps and plan to do a pulldown at the end, then i cant honestly give you advice because i dont understand how the 'framerate' of audio works. I wouldnt reccommend letting telecine apply pulldown and then you removing it, your just throwing away resolution for no reason. If you plan on doing any rotoscoping, always work in progressive.
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#3 Chris Bowman

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Posted 21 February 2009 - 10:38 AM

I too would like to know what canon means by "F". Since your shooting 1080i 24f, i would assume they just use f as short for fps, as in your shooting 48i 1080, which is technically 24fps interlaced.


As I understand it, Canon used CCDs that were designed to be interlaced. Since the chips can only read out every other line to a frame buffer in a single pass, Canon's solution was to attach two frame buffers, with the A field reading to one and the B field reading to the other simultaneously. The fields are then combined in the processing chip. Since this is not truly "progressive" (i.e. reading every line concurrently to a single frame buffer) Canon could not call it 1080P*.

Theoretically, if this is true, there should be no visible difference between 1080F and 1080P at any frame rate. In reality, some people swear that 1080F sucks, while others attest that there is no visible difference. All I know for sure is that 1080F on my XH-A1 gives visibly better resolution than 1080i, and that the frame rate goes all the way down to 24fps. The exposure levels indicate that 30F is not really 60i, nor is 24F really 48i. If they were really the same, the exposure levels would be the same. Instead, there is significantly higher exposure in the F mode exposures, just as you would expect in a "progressive" scan at that frame rate. I know for a fact that 60F and 60i give the same exposure level on my Canon, while 30F is much brighter.

*This information was something I read on another forum months ago. I can't find the original thread, and I don't know what evidence the original poster had to back up this info.
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#4 Brian Dzyak

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Posted 21 February 2009 - 11:16 PM

Hello everyone,

I'm DPing an ultra low feature and due to lack of money were are shooting on the XHA1 with a Redrock M2. Production has insisted that the footage shot every day is captured that night, but the only version of Final Cut we have on hand is Final Cut Express 4.

I am shooting in 1080i 24f, and I have done a lot of reading about the crazy Canon "F" modes, but I'm still a little confused. To add to my confusion, I can't find any info on what frame rate my sound mixer should be recording. He believes 29.97.

The only HDV option I have seen in this version of Final Cut is 1080i-60i. From what I understand, Final Cut will preserve the pulldown from the camera at that setting. If our post house (we don't have one yet) wants to remove the pulldown to edit in true 24p they should be able to, right? But if so, what should my sound man record his stuff at? 24p or 29.97? I would be in hot water if his sound discs can't be synced up with the video in post. :/

Thanks in advance for your help. We have just changed to this setup and I am starting to freak out.

-Neal


Your answer depends on what your final product should be. My understanding of most features is that your camera should be at 23.98 and your audio should record at 29.97.

That said, there is absolutely no reason you shouldn't first speak with your post department and ask THEM what they prefer/require...THEN you should shoot a short test tape (video and audio) and run it entirely through the workflow. You'll know then if there will be any issues before you really start shooting the project.

But ask your Editors first. If they are any good, they'll know precisely what the camera and audio should be set at per the finishing requirements as decided by the Producers.
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#5 Jim Hyslop

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Posted 22 February 2009 - 03:36 PM

I'm DPing an ultra low feature and due to lack of money were are shooting on the XHA1 with a Redrock M2. Production has insisted that the footage shot every day is captured that night, but the only version of Final Cut we have on hand is Final Cut Express 4.

I am shooting in 1080i 24f, and I have done a lot of reading about the crazy Canon "F" modes, but I'm still a little confused. To add to my confusion, I can't find any info on what frame rate my sound mixer should be recording. He believes 29.97.


We need more information about your workflow before we can answer completely.
  • How will you be syncing: via timecode or by sticks? If by timecode, how do you plan to sync the camera and recorder?
  • What is the destination format: film? video (SD or HD)? This does have a big impact on your workflow.
I haven't worked with the Canon, but I've worked with the Sony EX1 and Panasonic HVX200. Both of these cameras record 60 fps drop-frame, which works out to an actual frame rate of 59.94. The 30 or 24 frame rates are achieved by skipping selected frames. I would guess that the Canon works similarly, but I could very well be wrong (and, on re-reading Chris's post, I strongly suspect the Canon does work differently).

Push your producer to get the post production lined up ASAP yesterday. You cannot answer these questions in a vacuum - you need the editor's input. If your producer balks, then point out that any guessing you make at this point could end up doubling or tripling the amount of time (and therefore expenses) required in post. And, as Brian suggested, make sure you test the workflow to ensure things work the way you expect.

Another resource you can use for audio questions is the Usenet group rec.arts.movies.production.sound - a lot of very knowledgeable sound people hang out there, and they know all about the sync issues.

Also keep in mind that FC4 Express is ancient, in terms of software. I shot a small doc recently on the EX1, and the editor has FC4 Express. The only way we could ingest the material was to use a Macbook Pro with the latest FC suite installed to capture the clips, then render all the clips out to an NTSC miniDV. The editor then ingested the miniDV tape. Obviously, there's a huge loss in quality, so her edit will be considered an offline edit.

Edited by Jim Hyslop, 22 February 2009 - 03:40 PM.

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#6 Chris Bowman

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Posted 23 February 2009 - 12:56 AM

I haven't worked with the Canon, but I've worked with the Sony EX1 and Panasonic HVX200. Both of these cameras record 60 fps drop-frame, which works out to an actual frame rate of 59.94. The 30 or 24 frame rates are achieved by skipping selected frames. I would guess that the Canon works similarly, but I could very well be wrong (and, on re-reading Chris's post, I strongly suspect the Canon does work differently).


To clarify, the Canon XH/XL series cameras clock the CCDs to 24Hz, or a multiple thereof, in 24F mode (according to the manual). The HDV recording deck then takes this 24fps signal and records it as 24fps HDV without pull down. All signals off of the camera except the DV/HDV port (FireWire) are 60i, and the 3:2 pull down from them gives a somewhat disturbing off cadence jitter (which is what I suspect most people complain about), but the actual digital recording has a smooth 24 frame cadence.

Canon 24F HDV recorded tapes do NOT play nice with other decks, so a Canon HDV deck must be used for capturing to the editor, but once the computer has ingested it, there doesn't seem to be any difference from 24P.
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#7 Chris Bowman

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Posted 23 February 2009 - 01:38 AM

Hello everyone,

I'm DPing an ultra low feature and due to lack of money were are shooting on the XHA1 with a Redrock M2. Production has insisted that the footage shot every day is captured that night, but the only version of Final Cut we have on hand is Final Cut Express 4.

I am shooting in 1080i 24f, and I have done a lot of reading about the crazy Canon "F" modes, but I'm still a little confused. To add to my confusion, I can't find any info on what frame rate my sound mixer should be recording. He believes 29.97.

The only HDV option I have seen in this version of Final Cut is 1080i-60i. From what I understand, Final Cut will preserve the pulldown from the camera at that setting. If our post house (we don't have one yet) wants to remove the pulldown to edit in true 24p they should be able to, right? But if so, what should my sound man record his stuff at? 24p or 29.97? I would be in hot water if his sound discs can't be synced up with the video in post. :/

Thanks in advance for your help. We have just changed to this setup and I am starting to freak out.

-Neal


Honestly, I'm a little confused about your whole question on sound frame rates. Sound recordings aren't directly linked to image frame rates in digital video. For example, HDV specifies that audio be sampled at 48kHz regardless of the video frame rate (44.1 kHz is also permitted). If your sound mixer is overlaying the sound on to the video, it should always be done with the video its native frame rate. If you shot in 24F, you should be editing in a 24p timeline, and sound should be layered onto the footage in a 24p timeline as well, otherwise it will not sync exactly because the 3:2 pull down of the video will be slightly off cadence with the final 24p footage.

As for Final Cut Express not having 24P, any footage captured from a firewire port should still be an exact duplicate of the original data recording on the tape. If the software can capture your footage from your deck, it has imported 24p footage, and any pull down is added by the software. The file captured to the hard drive should be 24p regardless of what modes Final Cut Express supports, but it should only be edited and exported in a 24p timeline, which it sounds like it you will need another program to do.
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#8 Jim Hyslop

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Posted 23 February 2009 - 10:18 PM

Honestly, I'm a little confused about your whole question on sound frame rates. Sound recordings aren't directly linked to image frame rates in digital video.

Well, that's my take on it too, but if you're using timecode to sync, then you have to use the same tc rate for both the camera and the recorder, right?

--
Jim
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#9 Jason Hinkle (RIP)

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Posted 23 February 2009 - 11:18 PM

24p or 29.97? I would be in hot water if his sound discs can't be synced up with the video in post. :/


You can easily fix your audio to deal with interlacing by doing what is called "expanding" the audio where you adjust the pitch of the audio by 100.01% I would assume if you have pulldown removal the reverse would be true, changing the pitch by 99.99%. I am sorry I don't know about your particular camera, but I do know about dealing with audio syncing.

This is a standard practice in audio post when interlacing and pulldown are involved. It essentially slows down or speeds up the audio track exactly enough to deal with the difference in frames. The amount of pitch change is so slight that you cannot tell any difference at all.
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#10 Saul Rodgar

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Posted 24 February 2009 - 12:44 AM

Honestly, I'm a little confused about your whole question on sound frame rates. Sound recordings aren't directly linked to image frame rates in digital video.


I know a sound man who got in serious trouble while shooting a feature for assuming the above. He thought he could just record sound at 24fps on his recorder (since that was the camera speed) when they expected him to record it at 29.97 for HD / video post. No one realized what he was doing until the lab attempted to sync the footage to the sound and SURPRISE!! My acquaintance was nearly fired.

This is what he learned: When in doubt, always check, never assume anything.

The safest and smartest thing to do is to talk to the post production dept and clear the sound recording frame rate with them, as it has been suggested.
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#11 Chris Bowman

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Posted 24 February 2009 - 10:32 AM

I know a sound man who got in serious trouble while shooting a feature for assuming the above. He thought he could just record sound at 24fps on his recorder (since that was the camera speed) when they expected him to record it at 29.97 for HD / video post. No one realized what he was doing until the lab attempted to sync the footage to the sound and SURPRISE!! My acquaintance was nearly fired.

This is what he learned: When in doubt, always check, never assume anything.

The safest and smartest thing to do is to talk to the post production dept and clear the sound recording frame rate with them, as it has been suggested.


Of course you are right, making sure everyone is on the same page before the tape starts rolling is the best way to go about it.

I just realized that my profile info said that I was sound dept. instead of student. This was unintentional, and I apologize for any misdirection that it may have caused. I'm not trying to give my own comments any more weight than they deserve, and on this topic especially I may have appeared to be speaking with authority on a topic where I am not.
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#12 DS Williams

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Posted 02 March 2009 - 07:23 PM

Yeah Canon's 24f mode has confused me as well.

Essentially it's like the 24psf concept, accept the chips themselves run at 48hrtz, so it's not 'true' 24p, since each field is captured a 48th of a second apart from the one preceding it and following it. There is a definite loss of vertical resolution. But it still looks good to my eyes.
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#13 DS Williams

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Posted 02 March 2009 - 07:52 PM

[/list]I haven't worked with the Canon, but I've worked with the Sony EX1 and Panasonic HVX200. Both of these cameras record 60 fps drop-frame, which works out to an actual frame rate of 59.94. The 30 or 24 frame rates are achieved by skipping selected frames. I would guess that the Canon works similarly, but I could very well be wrong (and, on re-reading Chris's post, I strongly suspect the Canon does work differently).


You're actually incorrect there, Jim. The HVX200 and EX1/3, in 24p mode, capture true progressive frames and the sensor runs at 23.98 hrtz. The progressive frames are then embedded in a 60p data stream with the original frames flagged for extraction during editing. This is because the original Varicam used DVCPRO HD tapes that required a constant 60p data stream. And in the case of 24pA or 24p modes inside of 480i or 1080i, the P frames are split into fields and embedded with 2:3 or 2:3:3:2 pulldown into the 60i stream.
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#14 Jim Hyslop

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Posted 02 March 2009 - 09:04 PM

The HVX200 and EX1/3, in 24p mode, capture true progressive frames and the sensor runs at 23.98 hrtz. The progressive frames are then embedded in a 60p data stream with the original frames flagged for extraction during editing.

Thanks for the correction. I should have double-checked the manual before posting.
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