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Re: FCPX calculates video duration differently to QT7 and AV Foundation
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Re: FCPX calculates video duration differently to QT7 and AV Foundation

  • Subject: Re: FCPX calculates video duration differently to QT7 and AV Foundation
  • From: Jon Chappell <email@hidden>
  • Date: Thu, 09 Mar 2017 14:13:20 -0800
It tries to use the same timescale for everything but if it won't fit it will use whatever matches the original double up to 8 decimal places. But that didn't affect this particular example because the proposed timescale was 24000 and it was able to fit 1.24 exactly within that.

That's not the issue though. My calculations are correct for the value I am receiving, which is 1.24. The problem is that FCPX says 1.24 is wrong and it's actually 1.2399888889. I could certainly calculate that value and put it in the XML file but I don't know that value exists because I don't get that from QT or AVF.

FCPX, Premiere and CinePlay all say the file is 30 frames long. When viewing the file in QT Player 7 with the timecode mode set to Frames, it strangely says it is -10 frames long.

But now I do the calculations, 30 frames at 24*(1000/1001) would be 1.25125 seconds, so no-one's getting it right. Maybe the file is corrupt.


Regards,
Jon Chappell.
CEO, Digital Rebellion LLC.
http://www.digitalrebellion.com

On Thu, Mar 9, 2017 at 1:34 PM, Darrin Cardani <email@hidden> wrote:
Jon,

How are you calculating the numerator of the clip duration? How many frames is the clip?

Darrin

On Mar 9, 2017, at 1:03 PM, Jon Chappell <jonchappell@digitalrebellion.com> wrote:

I'm generating XML to add markers to a clip inside an event and FCPX is reporting that some of the values are not on frame boundaries. The original file's frame rate is 23.98.

The value it complains about is the clip duration, which I calculated as 29760/24000s. When I import the clip manually and let FCPX export an XML in order to compare them, FCPX chooses a duration of 892792/720000s.

My duration is therefore 1.24 seconds and FCPX's is 1.2399888889.

However, it's impossible for me to produce that duration because both the QuickTime 7 API and AV Foundation say the file's duration is exactly 1.24 seconds, so my calculation is correct according to the values I'm getting from those APIs.

For QuickTime 7 I'm using the following code:

double seconds = (double)mov.duration.timeValue / (double)mov.duration.timeScale;

I thought QT 7 might not be accurate enough so I tried AV Foundation using the following:

double seconds = CMTimeGetSeconds(asset.duration);

Both produce values of exactly 1.24 for the duration. My code does not round or modify the duration in any way.

So am I wrong or is FCPX?

Regards,
Jon Chappell.
CEO, Digital Rebellion LLC.
http://www.digitalrebellion.com
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      • From: Darrin Cardani <email@hidden>
References: 
 >FCPX calculates video duration differently to QT7 and AV Foundation (From: Jon Chappell <email@hidden>)
 >Re: FCPX calculates video duration differently to QT7 and AV Foundation (From: Darrin Cardani <email@hidden>)

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