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Soundtracks w different running times when remuxed?
#1
Hey guys,

I'm experiencing scratching head regarding remuxing tracks from DVDs to HD versions.

Everything is in sync, the image masters are the same, running at 23.976, so track should align by simple remux.

When I demux the tracks, they still are are the exact same length either opened in audacity, or VLC.

However when I want to remux them, they are off sync.

It looks like the tracks are running at 24fps to be the exact same, whereas the image master are at 23.976. ie when I reencode the tracks at 23.976 they come out sightly off sync, but at 24fps they are the right lenght.

How is this?
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#2
Are the tracks constantly out of sync or do they drift?
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#3
Nope I think they drift a bit, it's closer to sync by the end of the films.

I think it may have to do with the tracks actually being 24fps, but forced by a DVDflag to play at 23.976? But If I convert them with software, it's still off sync. Weird.

I also noticed the same happen to the video when I up it in fcpx, ie the video is about 12s shorter in the timeline at 23.976, but same lenght as the original m2ts when it's at 24fps, when the m2ts actually plays in VLC at 23.976, to the exact same longer lenght!

Here's how I did it:

Original DVD at 29.97, converted by removing the pulldown to 23.976
Demuxed all the audio tracks.
Aligned in FCPX in a 23.976 timeline and verified the videos are the same lenght. (though it displays at 12s shorter then the original source when put it the timeline)

Remuxed, constantly off sync.
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#4
OK here's what I discover.

If I set the timeline to 24p, that footage and sound plays in sync... at 23.976 even though the timeline is 24p!

What the hell is this?
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#5
On DVD your video track can be any framerate 24fps, 25fps, 30fps and converted to 29.97i using pulldown flags. It doesn't have to start out as 23.976. When you put the DVD into DGIndex select "Ignore pulldown flags" and see what frame rate it gives you. If it gives you 29.97fps then it means the interlacing is hard-encoded which is also possible with any frame rate.

Or try to ivtc it to 24.0 fps and check if you have one duplicated frame per 1,000 frames or not. If there's a dupe then the frame rate should be 23.976, but if there isn't then it should be 24fps.
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#6
I'm on Mac, but FCPX seems to have a "remove pulldown flag" when importing files, so I'm gonna try with this one.
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