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Compressor changes clip duration when exporting MPEG-2

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Denis Devlin
Compressor changes clip duration when exporting MPEG-2
on Dec 9, 2009 at 10:15:44 pm

I would expect 110460 frames (60P = 59.94 fps) to convert to 55230 frames (MPEG-2 down convert for NTSC SD dvd, 29.97 fps).

Instead the conversion produces only 55173 frames. I am using Compressor 3.0.5.

The duration of the original clip is:

10460 frames / 59.9406 fps = 1842.82 seconds. Or as displayed in FCP as drop-frame time coded duration: 30:42;48 (which likewise works out to 1842.8 seconds)

The duration of the exported MPEG-2 clip is:

55173 frames / 29.9703 fps = 1840.96 seconds. Or as displayed in FCP as non-drop-frame time coded duration: 30:39:04

The conversion using Compressor has shortened the 30 minute clip by almost 2 seconds when converting to MPEG-2.


Curiously, if I assume the source was actually 60fps (not 59.94 which is documented in the EX1 manual), then the math works out as:

110460 frames / 60 fps = 1841 seconds

With this assumption, for the starting clip (and contrary to what is displayed in FCP clip info,5 9.94 fps !), then the behavior of Compressor would make sense.

But, when I take a look at what happens to the audio, things get even more strange:

The audio comes out at the expected 55230 frames, 1842.82 seconds (or as displayed in FCP properties, a drop-frame duration of 00:30:42;24 (which works out to 1842.8 seconds when we calculate the ;24 as 24/30 seconds). Note: this is the camera audio which does play in sync when listening in fcp.

Audio / video sync is drastically messed up by an export. Almost 2 seconds off after 30 minutes.


I have deleted the FCP preferences file. I have tried various changes to the midi setup using the Audio Midi Setup utility.

My conclusion is that the Final Cut project that I am working in has somehow gotten very confused. There are no speed changes indicated in either the Video or Audio tracks. Everything is at 100.000 %. BUT, I have to admit that at an early stage of the project, I did adjust synchronization of an external audio track by something like 30 (60P) frames for the entire 30 minute clip. Presumably this somehow ended up confusing FCP even though the change bears little resemblance to the discrepancy of 112 (60P) frames that seems to be the current confusion.

Any ideas on how to re-constuct the FCP project so things will export correctly?

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Rafael Amador
Re: Compressor changes clip duration when exporting MPEG-2
on Dec 10, 2009 at 6:33:31 pm

Hi Denis,
This post should go to the FC Forum instead of the XDCAM.
I don't belong to the NTSC world, but for what you say (2 seconds difference in a 1/2 hour clip) some where you have a problem about DF TC with No DF TC.

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