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Frame rate difficulites

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Lisa Everton
Frame rate difficulites
on Mar 2, 2017 at 11:42:30 am

Hello all.
I am doing a PhD and analysing a lot of medical images in minute detail. The frame rate is critical. I am having trouble with some of the files which are at different frame rates. All files should have been acquired at original frame rate of either 25 or 30fps. Anything less is considered not high enough frame rate for level of analysis I need to do.
As an example, Final Cut Pro (sorry not sure which version) says the frame rate for a file is 10fps. The images play back slowly/ look at the wrong speed. However, the detail does not look compromised. It looks as if I can see everything I need to see but playing in slow motion/ strangely. Increasing the speed makes it looks strange too. I do not think speed is the issue.
When I toggle frame by frame, the frame only changes every 3rd toggle, so it looks like there are 2 duplicate frames. I am no expert at all, but from what I have read, I thought when changing the frame rate from higher to lower, i.e. 30 fps to 10 fps, this would mean deleting files. It does not look “choppy/ staccato” as if frames have been deleted - if the frame rate was actually converted from 30 to 10 wouldn't have lost a lot of detail?
Is it possible that when it was converted from the source file, that the output files have done something crazy with it (in this case mostly mp4, but also happened with avi). It's possible I may not be able to analyse these files at all if I cannot work out what has been done to them or get to original source file.
Many thanks for your help with this!


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Shane Ross
Re: Frame rate difficulites
on Mar 2, 2017 at 7:10:00 pm

OK, is the footage REALLY 10fps? Or is FCP only seeing it as 10fps? By this, I mean that when I did screen captures of my computer screen with certain software, I would tell it to do it at 29.97fps, and QT would report it as 29.97, but FCP would import it at 10. So I needed to basically smack it like you had to do with older TVs. By that, I mean I had to use CINEMA TOOLS to CONFORM the frame rate to 29.97. It kept the same speed, but basically added information that FCP could recognize and then it came in at 29.97fps.

Or is the footage really 10fps? If it is, then it will just look stuttery, as you mentioned, because instead of 30 pictures in a second, you have 10. It won't look an less clear...no detail is lost. You have the same image, just less of them per second, so it will stutter. FCP won't play back that 10fps at 30fps...a frame for frame playback...meaning REALLY SPED UP...unless you conform it as such. SO...if the footage really is 10fps, DO NOT use Cinema Tools to conform it, as it will do just that. If it is 10fps, leave it 10fps.

But FCP really doesn't work well with MP4...and will have serious issues with AVI. Anything that is NOT an FCP editing codec, meaning ProRes, DVCPRO HD, HDV, DV...anything you see listed in the Easy Setup...needs to be converted to an editing codec. At least with FCP 7 and earlier. FCPX and Adobe Premiere can handle this footage much better.

Shane
Little Frog Post
Read my blog, Little Frog in High Def


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Lisa Everton
Re: Frame rate difficulites
on Mar 3, 2017 at 9:04:45 am

Thanks very much Shane for you advice.

I have viewed the files in VLC, QT 7 & QT 10 & FCP and they all say its 10 fps. A colleague ran a computer programme on the files where it counted the frames and the duration and divided it to check the frame rate and that also came up as the same frame rate that these programmes read it at.

But the strange thing is, that when I viewed the same file in QT 7/ QT 10 and VLC, every time I advanced it frame by frame, the image moved, for every frame, whereas with FCP, the image only moved every 3rd time I advanced the frame. Why would that be? It doesn't look stuttery per se, just plays slower. But may be that it is essentially the same thing, on a continuum.

For the images I am looking at, I am measuring minute changes that can take place between three of four frames even, so if 20 frames are missing for every second, I don't think, if this really is the correct frame rate, I can use these images.
I think there may have been an issue earlier on - i.e. I think they were acquired at 30 fps but when recorded, perhaps the default frame rate was wrong? Or some other parameter that makes a difference?
My guess would be I have to track down the source files if I can??


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Shane Ross
Re: Frame rate difficulites
on Mar 4, 2017 at 7:21:53 pm

Yes, try to track down the source.

Not sure what's happening on your end when you view things. Not much I can really figure out without actually looking at the clip, and I don't want to ask you to supply it. Perhaps when playing frame by frame, you are seeing every frame advance because you are literally saying "next frame please." But when playing back...it does it on a per-second basis. I can't say for sure.

Shane
Little Frog Post
Read my blog, Little Frog in High Def


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Lisa Everton
Re: Frame rate difficulites
on Mar 7, 2017 at 9:14:00 am

Thanks Shane for your advice. I'll see if I can track the source files. Best wishes, L.


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