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Weird stuff... so the video editor, working with FCP on Mac exported a .mp4 @ 25 fps (true -- I even saw the stream info) and sent it to me. Even before I opened the file (PC) I went to its properties and it said 15.48 fps. I opened it on another PC and it was the same 15. I imported it to Cubase and there were the 15 fps.

As if it's not weird enough, the lentgh of the file labeled @ 15 fps is still the same 8m14s as has the "original" at 25 fps... at the file properties.. Imported at Cubase, the playback is actually FINE, but the thumbnail cachet generated in the timelime stretches until around 13 minutes, although the video playback stops at the correct end of the video at 8m14s. So I checked out the box dialogue of video import and it appeared 13m19s of lenthg!!

I also noticed that the number of frames are very approximate of what should be the 8m14s @ 25 fps (494 secs * 25 fps = 12350), whereas the "15.48 fps" has 12359.

Sent the file back again to the video editor and it was nice and neat @ 25 fps!

Any thoughts on what is happening here? Thanks!

  • I don't have an answer to why that's happening. It's realllllly odd, if not scary. An option though, if you need to get the .mp4 working, is to demux and remux it using a program like mp4box. Also if you haven't already, take a look at what codecs you have; perhaps that's where the problem is. I'd be curious to see what VLC thinks the framerate is. Good luck! – Miles B. Apr 12 '12 at 2:29
  • VLC thinks it's 25 fps... mind blowing. – Melissa Pons Apr 12 '12 at 10:59
  • Qt thinks it's 15.48... – Melissa Pons Apr 12 '12 at 11:17
  • Yeah, VLC's quite the maverick. :P – Miles B. Apr 12 '12 at 16:20
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The golden mantra: "FCP does that". Try importing the project in a new project, then exporting your video again. Quicktime's container header is incredibly flexible and there's maths in there and very often (especially with FPS other than 29.97) FCP gets things wrong in that area, then Quicktime has to guess.

If you're brave enough to see the guts of the video and do some maths, grab an utility called Dumpster, and, while you wait for your editor to give you a new video, look at the numbers:

In the movie header "mvhd", look at timeScale, then in the video track header look at timeScale and duration. Best if the two tracks have the same values. Then look at the duration values for the movie header ("mvhd") and video track header ("trak > mdia > mdhd"). Divide duration by timeScale and you should get number of seconds.

To get the framerate of the video track, see "trak > mdia > minf > stts". Dividing the video track timeScale by sampDur should get you the frame rate. One of those values is wrong. The Quicktime player corrects it before showing you the video (based on some common sense, assumptions, and knowledge about the shortcomings of FCP). I assume not the same happens with the Quicktime or QTKit libraries which other software use to import and play the video.

alt text

Now for the kicker: You can click to edit these values, then press Cmd+S. Backup your file.

  • 25 FPS at timeBase of 600 - sampDur should be 24
  • 25 FPS at timeBase of 30000 - sampDur should be 1200
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Did you get 25fps burnt in timecode? If you had then you could put it in a 25fps timeline & step through it 1 frame at a time & prove if it is right/wrong...

Working on anything in post production there are reasons for certain approaches eg I never accept a video to work to unless it has - burnt in timecode - SMPTE leader with 2 pop - tail 2 pop

With these you can prove whether the LFOA is correct, whether the video is the correct speed & the burnt in timecode is correct...

As said elsewhere plenty of times mp4 is not a video format to do post work to - it uses interframe compression & you need a format with discrete frames eg photoJPG or DV

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