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Frame Rate Bug

Jan 22, 2014 3:09 PM

I think I've stumbled upon a bug and could use some verification.

 

In short, I cannot get any Adobe software to correctly output 24fps media to same.

 

The longer version is that I've got some 24 fps media at exactly 24, not 23.976.  Premiere Pro reads the media correctly at 24.  (Though on a side note, both Media Browser and Prelude read it incorrectly as 23.98.)

 

I've created a matching sequence and exported that one clip (no edits, no effects) using both Queue to AME and direct Export from PP.  I've also tried the Render Queue out of AE for the same clip in a matching composition.  I've also tried Ingest in Prelude with a Transcode.

 

I've tried exporting to DNxHD, UT, MPEG2-DVD, H.264, H.264 Blu-ray, and JPEG image sequence.  The export specs match the 24 fps for all formats.

 

This was tested on both Windows 7 and Windows 8.1.

 

In every single case, brining that exported media back in and placing it directly over the original, the frames to not match.  The audio is perfectly in sync, the durations are correct down to the frame.  But as I move through the footage, the frames begin to mismatch, so that if I click the eyeball to turn off track 2 and see the original underneath, it's a different frame!  They start off identical, and they end up syncing again near the end so there's no duration discrepancy.  But the frames in between do not match!?!?!?

 

This does not happen with my 23.976 media, only with the 24 fps media.  It does seem to take some time for the drift to pronounce, like 5 to 10 minutes of media.  It didn't show up on shorter clips.

 

The clip tested was spanned into two files, so I wonder if that plays a part.

 

Can anyone with genuine 24 fps media test this?  It's a pretty serious bug if such media will not export frame accurate.

 
Replies
  • Currently Being Moderated
    Jan 20, 2014 6:03 PM   in reply to Jim Simon

    Exactly what media (camera footage / codec) are you using in your test?

     

    I am guessing maybe your hacked GHx ?

     

    Haved you tried anything else?

    Whats the issue if...

     

    The audio is perfectly in sync, the durations are correct down to the frame.

    They start off identical, and they end up syncing again near the end so there's no duration discrepancy.  But the frames in between do not match.  WTF!

     

    Sounds like a GOP preview  type of thing .

     
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  • Currently Being Moderated
    Jan 20, 2014 9:31 PM   in reply to Jim Simon

    My camera won't produce 24fps, just 23.976 so unless you have a short 24fps clip you can let us use for the test, I suppose exporting something from After Effects is the next best bet.

     
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  • Currently Being Moderated
    Jan 20, 2014 9:47 PM   in reply to Steven L. Gotz

    I interpreted some 23.976 as 24fps in Ae and exported it to 24fps. Premiere Pro sees it as 24fps.

     

    I repeated the 9 second clip over and over to achieve a 20 minute sequence which I am exporting to H.264 now. When it is finished, I will bring it back into Premiere and see how they line up.

     

    If they are identical, you will need to provide footage or find someone who has some. But if this test shows a discrepency, then Adobe will have an easy way to replicate the problem.

     
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  • Currently Being Moderated
    Jan 20, 2014 10:01 PM   in reply to Steven L. Gotz

    My test failed to replicate the issue.

     

    So, footage produced in After Effects comes out 24fps according to Premiere Pro and exporting it and bringing it back in revealed no issues.

     

    So there must be something about your footage.

     
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  • Currently Being Moderated
    Jan 21, 2014 10:17 PM   in reply to Jim Simon

    Well, if you want to post one that shows the problem, I don't mind downloading it to help out. I just don't have a way to shoot 24fps exactly. Not that I know of, anyway.

     
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  • Currently Being Moderated
    Jan 23, 2014 6:59 AM   in reply to Jim Simon

    Jim,

     

    Set up your camera pointed at a digital clock.

     

    Run 20 minutes or so.

     

    That ought to make comparing frames a lot easier.

     
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  • Currently Being Moderated
    Jan 23, 2014 12:21 PM   in reply to Jim Simon

    Only if it has parts of a second on the clock.

     

    A stopwatch would be better.

     
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  • Currently Being Moderated
    Jan 23, 2014 1:28 PM   in reply to shooternz

    I would be willing to bet that there are stop watches on the Internet that you could point a camera at. Good idea Craig.

     
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  • Currently Being Moderated
    Jan 23, 2014 1:31 PM   in reply to Steven L. Gotz

    Smart phones have them.

     
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  • joe bloe premiere
    4,391 posts
    Dec 6, 2009
    Currently Being Moderated
    Jan 23, 2014 1:37 PM   in reply to shooternz

    Dum phones don't (mine).

     

    Online Stopwatch

    http://www.online-stopwatch.com/full-screen-stopwatch/

     
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  • Currently Being Moderated
    Jan 23, 2014 9:44 PM   in reply to joe bloe premiere

    Back in my days working on OnLocation, I often tested timecode-related matters by shooting footage of both  a stopwatch and a mirror showing the camera's LCD flipped forward, with the timecode on.

    Not particularly relevant to this thread, but when I was checking for dropped frames nothing beat shooting a pendulum like this.

    And my favorite trick for testing audio sync: snapping clothespin  in front of the camera every few minutes. On playback, there was no mistaking the frame when it snapped and the spike in the audio. When retrieving the C47 from wherever it flew became tiresome, I even rigged one up with a short strand of monofilament that I'd loop around my finger.

     
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  • Currently Being Moderated
    Jan 24, 2014 11:03 PM   in reply to Jim Simon

    Could it simply be a long GOP issue? That the preview is screwing it up? Have you tried changing your preview file codec? Does that codec even matter if you don't render?

     

    Sorry. More questions and no answers.

     
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