F3: F3 matching alexa at 24p

L

litpixel

Member
Brief outline I have just shot one day on a feature second camera. There were very brief checks done before shooting and I went ahead with 23.976 as the Alexa was in 24p.

now the asst editor has said the first days rushes from the F3 have been taken into avid and have significant motion blur. they play fine for me on the pix 240 I recorded them on. does anyone know if this is probably an avid thing and they need to change their settings? or should I be shooting in 25p and then reducing in post? anyone any experience of this?

thanks
 
If the F3 was set for 23.976 and the Alexa was set to 24.000 and the Avid timeline is set up as 24.000 then there's a good change the "motion blur" is from the computer system doing a poor job of conforming the 23.976 to 24.000

I would make a backup of the F3 footage, lock it away, then try using something like Cinema Tools to conform the F3 footage to 24.000

Of course, this is assuming you want a film out final delivery... if it's just going to get played on digital equipment it would likely make more sense to have shot and conformed to 23.976.


DISCLAIMER: I haven't worked with the Alexa - this advice is based on experiences with editing and frame rate conversions.
 
thanks for that. yes the issue is the 24 timeline. the main camera is shooting 24p for print. the asst editor has just taken in 1 days rushes from the F3 and flagged significant motion blur when he viewed it. I'm guessing the system is not set up right and that he took it in not aware it was 23.976 and not 24p and had not allowed for that. but I'm not and editor so I don't know. I just really was wondering if 23.976 and 24p would normally match each other without picture degradation. we are not worried about the sound as it is not used for anything more than seconds here and there.
 
If you don't retime the footage than the editing software has a limited set of choices:
1. play the footage at the correct time rate by blending frames
2. play the footage at approximately the correct timerate and occassionally drop frames to match - this means there will be some intermittent drift
3. play the footage back at a rate of 24.000, which will generate a constant amount of drift, and will be slightly faster than real time - but will have no blended frame blur

If it's for dailies, the editor should just do the F3 stuff in a 23.976 timeline.
Other than that, the editor should be instructed to conform the F3 footage to 24.000
 
thanks for the response. I'm not an editor so I'm a little confused by it all and some of the terms you use are beyond my knowledge. But I will pass the info on. I am hoping the asst editor is just not familiar with the procedures you mention above and that one of those is a good fit an fix to continue using the F3 on the job. right now he is just saying there is bad motion blur on what he has taken in. and I was trying to understand why as it is playing back fine for me. there is a bit of inexperience here all round and hence a lot of panic when stuff is not doing what it is supposed to do. and at present he does not know the solution so producers are thinking of dumping the F3. I was under the impression that when sound is not an issue then putting 23.976 footage together with 24p should be a good fit and not result in picture degradation. And I think that is still the case.
 
Just imagine, hypothetically, that you shot footage at 17fps, and needed it to play back in real time, as part of a movie being projected at 24fps. In this hypothetical scenario your source material only has 17 real frames of data per second, and you need to display those 17 frames across 24 frames in the output. You can either repeat frames, which will make the footage appear to stutter, or you can dissolve or blend the frames together, creating more motion blur, to cover the lack of real frames of data.

That same principle is happening to your footage now. But the difference between 23.976 and 24.000 is so minute, that you can instead use software like Cinema Tools to instruct the software to play the footage recorded at 23.976 back at 24.000 - this speeds the footage up ever so slightly, but it's hard to notice, and the audio can be stretched and tone pitched to cover if need be.

If the editor doesn't bother to do this, when the 23.976 footage is put on a 24.000 timeline, it will blur.
 
that is brilliantly explained. thank you. I am very familiar with frame rates and the like and what happens to duplicate frames etc. depite being ignorant of some technical terms. but your mention of cinema tools is perfect. something definite I can say to do to avoid producers simply dismissing the F3. To me 23.976 and 24 are so close it was hard to imagine there being such an issue unless some settings were off. They have been taking everything into a 24 timeline. so it would stand to reason the 23.976 has not been altered to account for this. hence the motion blur.
 
This is basic stuff. The editor probably needs to get his act together.
There should be virtually no difference between those two frame rates if conformed properly.
 
yoclay said:
This is basic stuff. The editor probably needs to get his act together.
There should be virtually no difference between those two frame rates if conformed properly.
Click to expand...

There's a HUGE diffrence between the framerates on a filmout, and this is for filmout....

I think the edit asist has done the best thing for everyone, flagging it early

Blended frames will never pass QC for a filmout, optical flow means additional expence and some shots will never work without a ton of roto to clean up boundry violations - best option is to change the media's metadata to 24true, and then audio has to work as best it can in this case

this is going to be expensive for the producer's no matter what, the project conform just got much more complicaed, the audio house also has some heavy lifting to do

I'd make sure the camera's shooting at 24true from this point on!
 
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litpixel said:
To me 23.976 and 24 are so close it was hard to imagine there being such an issue unless some settings were off.
Click to expand...

It is an issue though, because to edit all media has to be playing back at the same speed. This speed difference is enough to difficult to solve visually (frame blending, optical flow, etc), but it's enough to cause sync drift issues even within a scene.

I hate to say it, but the F3 never should have been used as B camera in this instance, really. It can't do 24.000. That was the first mistake.

Like others have said, the motion blur is a bad frame blending going form 23.976 to 24.000. That's gotta be turned off in Avid. So that's fix #1.

So after that's fixed the problem becomes simple or complex, depending if B cam has to sync with A cam and sound:

Scenario A: It's going to be a problem for the editors if they wanted the 2 cams to sync in multi clips for scenes. You can conform the 23.976 to 24.000, but then sync falls off all over the place for the F3 media.

Scenario B: Now if the F3 is just non-sync shots peppered throughout the edit, and the shots don't have to sync the sound, then the media should just be conformed or interpreted at 24.000 (i.e. sped up) and stuck in the edit here and there and everything will be fine.

If the F3 shots are truly short, I'd consider doing a completely dumb "nearest neighbor" frame rate conversion, which means 1 frame will be duplicated every so often to keep sync with the 24.000 Alexa and sound. I'm not smart enough to do the math and figure out how often a duplicate frame would be inserted using that method, but I think it's going to be infrequent enough to be worth a shot. I don't know if Avid can do that internally. This would fix scenario A.

[edit: some suspect math on my part thinks that using the above method, 1 duplicate frame would be inserted about every 40 frames or so]
 
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A single duplicted frame is an automatic QC fail of the entire film reel, and blended frames are as well....

the issue is NOT stuttering in the offline, that's trivial - the issue really is a fail on the QC report on the master and a $10,000 per reel charge to film it out again...

No-one's who's finishing/gradeing for filmout would let it past anyway, so it's gonna be sorted, now the question is how much is it going to cost and when in the process will it happen?

The edit assist did a good thing by flagging it early when the options are more open, and not so costly

All this changes if it's only going to broadcast... then blended frames might be acceptable, likely a "2" or a "1" - but not a "3"....

For the web? who cares..one can send pretty much anything out the door
 
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I'm not sure I understand this latest information. As I said earlier sound is not an issue here. this camera is only being used for cutaways and stuff missed and not for any long takes so it never has to be sync for long periods. but are you guys now saying that any 23.976 footage used in a 24 frame timeline for film out is unusable? because qc will just not accept it? my initial advise was that 23.976 was close enough to be used in small amounts with 24p to not cause issues like this
 
If it's converted to 24 before mastering, it will be fine,

as other's have mentioned before me - i also would advise changeing the metadata on the master footage so it's interpreted as 24p before injesting into the off-line system, that's the cheapest, simplest, cleanest answer, then it's just another piece of 24p footage to conform and grade


If it's all MOS then please ignore my comments re; sound & sync

And then thank the edit assist for flagging it early

I have graded F3/Slog and Alexa/logC for filmout- they match very well in terms of color & density
 
thanks Dermot. yeah thats why we picked it. with the pix now doing 444 we were able to take a lovely picture from it and initial comparisons with a quick grade showed it was matching really well. the frame thing is solved then by doing as suggested above and using cinema tools to conform the footage for offline to 24?
 
litpixel said:
thanks Dermot. yeah thats why we picked it. with the pix now doing 444 we were able to take a lovely picture from it and initial comparisons with a quick grade showed it was matching really well. the frame thing is solved then by doing as suggested above and using cinema tools to conform the footage for offline to 24?
Click to expand...

At my end of the process i usualy don't see these issues in films, the assists i get to work with are pretty tight, so the issues are sorted before the footage makes it into my hands, when it has happened it's been for TV shows only,

End game is that i have no idea how cinematools works, but likely some assists i work with do!

When i do see something like this, my answer has been to force the footage into a "frame for a frame' and then use the editor's in point, and let it slide where ever it goes to, then call in the post sup to review, and issue newly revised refrence QT's for the sound house.. i typicaly finish shows in pretty flexiable systems like Quantel Pablo or Avid DS where we can quickly (ish) deal with stuff like this

Sound still needs to see the revised frame range to get foley/sfx sync right

All that is extra (unbudgeted) costs to production

Best sorted early! Can the assist offer any thought? Seems he/she was sharp enough to catch it in the first place
 
the assist is doing research to try to come up with the best solution. the thing the assist has flagged is that there is motion blur on the F3 footage when its played on the timeline. He's not sure what the fix for that is but it sounds like the fix is that it wasn't conformed properly for 24 and was simply taken in 23.976 and dropped onto the 24 timeline. so once its taken in properly and conformed to 24 and then placed on the timeline I am assuming the motion blur disappears. and you are then just dealing with a 24 edit. again without the sound issue as its selected shots. the notion of qc failure etc that you mentioned is new info. and one I'm trying to understand. as I mention again I'm not an editor so I just assume that pictures conformed to 24 and not needing a big sound adjustment can be used for film out without issues.
 
Can the PIX not record the 23.98 output into a 24p wrapper? I thought it was able to do that. (but I live in PAL land so I've never had to deal with the complications of 24p/23.98p)


I'd also suggest reconforming the masters to 24p and take the miniscule speed change. We've never had substantial issues with the 4% slowdown we got from converting 25p to 24p for filmouts down here.
 
thanks Grug. yes in theory the pix can be forced into 24 frames from a 23.976 input but it most likely leads to artifacting. and that was Matts advice from sound devices so thats not a road to go down. all I knew beforehand was that 23.976 was so close to 24 that if sound was not a factor then we were good regarding matching on the timeline. the motion blur seems to have come from not telling the avid to interpret the 23.976 as 24. But now there is a suggestion that any 23.976 thats been altered for 24 film out will fail a qc. and thats a big deal. so I'm trying to clear that up now
 
Lit, I missed your earlier info that the F3 was all MOS or short B-roll stuff, so yes a speed up from 23.976 to 24.000 before cutting will solve everything

And Dermot, I knew about duplicated frames failing, but it would be a way for the editor to keep sync with other elements if needed to get the cut done, and then snip out the duplicate frames after the cut was built.

Sounds like it's all gonna be ok! Just gotta get that assist to turn off frame blending! :-)
 
litpixel said:
thanks Grug. yes in theory the pix can be forced into 24 frames from a 23.976 input but it most likely leads to artifacting. and that was Matts advice from sound devices so thats not a road to go down. all I knew beforehand was that 23.976 was so close to 24 that if sound was not a factor then we were good regarding matching on the timeline. the motion blur seems to have come from not telling the avid to interpret the 23.976 as 24. But now there is a suggestion that any 23.976 thats been altered for 24 film out will fail a qc. and thats a big deal. so I'm trying to clear that up now
Click to expand...

alot of shows (most really) are done at 23.98, that's not an issue for filmout, a frame is always a frame, the issue is mixing framerates, then you have to deal with one of; blended / held / optical flow'd frames...

there's where the issues arrise
 
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