Latest post Sat, Jul 14 2018 5:07 PM by danny. 9 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.

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  • 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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    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]
  • Sat, Jul 14 2018 12:59 AM In reply to

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

    How were you doing that export?

    If you were doing a Same as Source export you were invalidating the changes done in the source settings.

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  • Sat, Jul 14 2018 1:37 PM In reply to

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

    Hi JC

    Seems a long time ago! As I said earlier in the thread, in the end I broke the sequence into 3 chunks and speed-changed in Cinema Tools successfully. There seemed to be a weird sync drift in Avid on export that didn't fit the expected maths - 5 frames as opposed to 82 frames per hour, as kindly explained by Job. Anyway, now I know that CinemaTools can handle stuff in smaller doses, I have a reliable workaround. It wouldn't have been an issue if Cinema Tools had been able to handle 3-hour-long ProRes HQ files.

    The reason I have had to deal with all this lately is making trailers and re-mastering entire 3 hour shows for both 24fps and 25fps DCP versions from both 25fps archive masters and 23.98 masters. During this process I thought what would be really useful is a feature that would allow Avid to play back a 25fps sequence frame-coherently at 24fps (and vice-versa) within the same project, ie: without changing projects. But I seem to remember being told this was incredibly difficult to engineer - contrary to the old Steenbeck days where one would simply push a button for the editing table motor to run at a slower or faster speed!

    What would be brilliant is for someone to invent a stand-alone app or tool that took care, in one click, of speed-changing, say a ProRes exported file (à la Cinema Tools) and then applying the required pitch change to the audio, spitting out a speed-changed video and pitch-corrected audio file at the other end, whilst retaining the standard 48000Hz sample rate. Instead of the tortuous multiple processes one usually goes through to treat the video and audio separately and then re-combine them.

    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]
  • Sat, Jul 14 2018 3:46 PM In reply to

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

    danny:
    What would be brilliant is for someone to invent a stand-alone app or tool that took care, in one click, of speed-changing, say a ProRes exported file (à la Cinema Tools) and then applying the required pitch change to the audio, spitting out a speed-changed video and pitch-corrected audio file at the other end, whilst retaining the standard 48000Hz sample rate.

    Sounds great, but the pitch correction itself is such a delicate thing, that this is far from an easy task.

    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]
  • Sat, Jul 14 2018 5:07 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

    The pitch-change is something that even Audacity manages pretty well - maybe not perfect, but I've had really acceptable results, even with piano, orchestral and operatic pieces, although Pro Tools is marginally better. It just needs automating, then resampling to 48k within one tool. One day maybe...

    Job, do you think that asking an NLE to play back a 25 fps seq at 24 fps is ever going to be feasible? With my recent jobs of UK 25 fps to both 24fps and 25fps for DCP distibution, it would certainly make life a lot easier. Even being able to get a precise "duration in-out, as if played at 24 fps" without having to export, convert to 24 fps and open in a 24 fps project, would be useful.

    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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