Latest post Tue, May 15 2018 7:47 PM by danny. 5 replies.
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  • Fri, May 11 2018 4:23 PM

    • danny
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    23.98 at 24fps source settings, sync drift on export

    Sorry if this has been answered already, but I had to link to a 3 hour 23.98fps file (too big for Cinema Tools to handle) into a 24fps project for export at 24fps. I changed the source settings of the clip in Avid to play back at 24. All appeared fine in the timeline and it held sync on playback. However, on export the audio in the ProResHQ QT slipped by approx 2 frames every hour. To check I re-linked to the exported clip and confirmed the picture was frame coherent and matched the timeline, but the audio waveforms were slowly drifting by over 5 frames in 3 hours. It's as if the source settings of the audio were ignored on export.

    There are external workarounds with exporting the audio separately and changing sample rates to 48048 Khz etc, but I had hoped that the direct export from Avid would have matched what one sees when playing the timeline. I wonder, is this a bug or a feature...?

    Danny

    Mac 3Ghz 8-core cylinder Xeon E5. 32GB 1866Mhz DDR3. AMD D700 graphics x2. OS 10.12.6 with MC/Symphony 8.9.1 [view my complete system specs]
  • Sun, May 13 2018 9:15 PM In reply to

    • jef
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    Re: 23.98 at 24fps source settings, sync drift on export

    Not sure of an answer, but as an experiment, I would try doing an audio mixdown in the 24 sequence and then try an export of that.

    Also, were you using Same As Source export or the old school version of QT export?

    Jef

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  • Mon, May 14 2018 6:11 AM In reply to

    Re: 23.98 at 24fps source settings, sync drift on export

    A .1% drift would be 1 frame every 00:00:41:16 – so 1 frame every hour is another issue.

    Media Composer /w Symphony option | PT-HD | Win7Pro64 HP | OSX MBP | ISIS5000 | Nitris DX | Artist Mix & Transport & Color | AJA T-Tap | Decklink... [view my complete system specs]
  • Mon, May 14 2018 10:16 PM In reply to

    • danny
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    Re: 23.98 at 24fps source settings, sync drift on export

    Thanks Jeff,

    Will try audio mixdown and then export when I get a free moment. Hadn't thought of that - sounds like it should "lock" the audio at the right speed / length. I'll post my findings. I do think it's an illogical bug / feature though.

    Job - it was less than two frames per hour but more than 1. So around 5 frames in three hours is about right.

    regards, Danny

    Mac 3Ghz 8-core cylinder Xeon E5. 32GB 1866Mhz DDR3. AMD D700 graphics x2. OS 10.12.6 with MC/Symphony 8.9.1 [view my complete system specs]
  • Tue, May 15 2018 3:26 PM In reply to

    Re: 23.98 at 24fps source settings, sync drift on export

    danny:
    Job - it was less than two frames per hour but more than 1. So around 5 frames in three hours is about right.

    1 hour of drift (3600 seconds) divided by 00:00:41:16 (41.66) is 86.413826212. So ~82 frames.

    Media Composer /w Symphony option | PT-HD | Win7Pro64 HP | OSX MBP | ISIS5000 | Nitris DX | Artist Mix & Transport & Color | AJA T-Tap | Decklink... [view my complete system specs]
  • Tue, May 15 2018 7:47 PM In reply to

    • danny
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    • Joined on Sun, Jan 24 2010
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    Re: 23.98 at 24fps source settings, sync drift on export

    Hi Job,

    In the end, I broke the three hour 23.98 clip into 1-hour sections and changed them successfully in Cinema Tools to run at true 24fps, with audio at 48048 Khz. I then linked to those, cut them into a 24fps sequence, re-joined them up and exported SAS. This is a method that has worked fine for me in the past, but was stumped when Cinema Tools couldn't handle the 3-hour clip.

    Hence plan B to change the source settings. I have verified that the duration was identical to the above method and played back in sync. It was only on export that things went awry and was able to see a 5 frame drift over three hours.  I haven't yet had a chance to try doing an audio mix-down before export, as I have now solved the issue by using Cinema Tools as above.

    I understand what you're saying re sync drift caused by 23.976 vs 24fps being 82 frames per hour. I'm saying the 5 frames over three hours is what I actually experienced when exporting a 23.976 clip that had its source settngs changed to 24 fps. Which is why I think it's a bug that needs fixing.

    regards,

    Danny

    Mac 3Ghz 8-core cylinder Xeon E5. 32GB 1866Mhz DDR3. AMD D700 graphics x2. OS 10.12.6 with MC/Symphony 8.9.1 [view my complete system specs]
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