Exported file changing run time

Posted by MetalGuru 
Exported file changing run time
May 17, 2017 09:22AM
I have a ProRes 4444 24p film master, which I'm exporting from FCP7 to ProRes 422. However, the exported file is running almost 6 seconds longer. Any ideas why this is happening? I'm baffled.

4444 file = 104:25:14

Export -> Quicktime Movie -> ProRes 422 1920 x 1080 24p

422 file = 104:31:21
Re: Exported file changing run time
May 17, 2017 09:37AM
OK, this is strange - it's MPEG Streamclip that's telling me the file is longer. Importing it back into FCP7, it's the same.
Re: Exported file changing run time
May 17, 2017 08:15PM
I assume you're reporting timecode 01:44:31:21 as 104:31:21 and timecode 01:44:25:14 as 104:25:14, and that you mean "a bit more than 6 seconds longer" where you write "almost 6 seconds longer".

The apparent lengthening of your video is the result the legacy nightmare of cinema's 24 fps vs. NTSC-based 23.976 fps.

The FCP7 sequence presets denoted 24p are really 23.976 fps. You can verify this in Sequence > Settings. (Note: 23.976 is written 23.98 in Appletalk.) Your ProRes 422 export is probably a 23.976 fps file. That is, its metadata probably says 23.976. The file's real content is probably 150374 frames, and MPEG Streamclip correctly calculated its duration to be 01:44:31:21. 150374 frames played at 24 fps runs 01:44:25:14 for comparison.

An FCP7 timeline can be set to 24 fps or to 23.976 fps. And exports will then be 24 fps or 23.976 fps, respectively. However, while working in the timeline, h:m:s:f timecode shown in the box will always be as if it is a 24 fps timeline. So for a 23.976 fps timeline, FCP7 shows false durations. You would need drop-frame timecodes in order to show true durations, but FCP7 doesn't allow these for its 23.976 frame rate.

By not knowing whether your files are 24 fps or 23.976 fps and not knowing whether your timelines are 24 fps or 23.976 fps you can make some trouble in FCP7. For example, if you paste your 150374 frame 23.976 fps thing into a (non-empty) 24 fps timeline, FCP7 will silently "fix" your thing by inserting 151 duplicate frames in it.

Dennis Couzin
Berlin, Germany
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