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Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem

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Gareth Randall
Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Sep 23, 2011 at 12:15:18 pm

We have a workflow that involves transcoding 1080p from 23.98 AVCHD to ProRes 422 and then using Cinema Tools to conform to 25fps. 50% of the time it works fine, 50% of the time the audio runs out of sync with the video after the conform.

AIUI, Cinema Tools is just altering the metadata of the QT file so that it gets played at a different framerate, so is there any reason why sometimes the audio stays in sync and sometimes it doesn't? The audio is *always* in sync after the transcode to ProRes (I make sure to spot-check it at the start, middle and end of the file), it's only the two-second job of the conform in CT that causes the problem (or not).

Something I haven't yet attempted is doing the framerate conversion in Compressor as part of the transcode to ProRes. Will this add a major extra overhead to the transcode time? We're just in the process of setting up a 4-machine Qmaster cluster (2x4-core iMacs, 2x8-core Mac Pros), so I guess that would help offset it.



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Gareth Randall
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Sep 23, 2011 at 1:10:23 pm

Just tried changing the framerate within Compressor - predicted transcode time went up from 4 hours to 26 hours on a 2-machine cluster. Ouch.



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John Pale
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Sep 23, 2011 at 2:38:05 pm

Are you noticing the sync problem in FCP?

CT changes the sample rate of the audio to an odd one (I forget the exact rate). FCP may be trying to deal with it on the fly...and failing, as usual. The sample doesn't match the sequencevand sync problems occur.

Have you tried doing an item level render on the audio?


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Gareth Randall
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Sep 24, 2011 at 3:15:12 pm

CT changes the sample rate to 50.4 KHz. If it causes an audio sync problem, which as I say is about 50% of the time, it happens in FCP and any media player you try and play the file in.

FWIW the workaround is simple but still a chore. I export the audio from the 23.98 version, note the exact duration of the 25fps version, and then use Audacity to speed up the 23.98 audio to match (with pitch change). Then I just paste it back onto the 25fps version in QT Player 7.

I did try doing the speed change in Soundtrack Pro, but that seems to insist on chopping out samples to retain the original pitch, which causes some very audible artefacts. I haven't found a way of doing an Audacity-style speed-and-pitch change in STP.



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John Pale
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Sep 24, 2011 at 6:58:32 pm

[Gareth Randall] "CT changes the sample rate to 50.4 KHz. If it causes an audio sync problem, which as I say is about 50% of the time, it happens in FCP and any media player you try and play the file in."

Does the sync problem resolve if you render the audio?


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rd Martin
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Nov 11, 2011 at 12:51:01 am

I am having the same problem with the out of sync audio
For me I am going from 25 to 24fps in cinema tools.
Alright, I put the h264 video codec file into compressor and converted it using app pro res 422
It looked great and everythings good.
Than I open cinema tools opened the clip the conform button was available to push. I conformed it to 24fps from 25

The orginal duration of the video was 17:15 and now the duration is longer at 17:58
If I am taking away frames why would it be longer?

I put it into fcp and the dialog is out of sync with the last few seconds of the video having mute audio because track already went through. It is also out of sync when playing it in QT

How do I fix this syncing issue?


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Michael Gissing
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Nov 11, 2011 at 1:00:13 am

Changing 25 to 24 means the video runs 4% slower so it will be longer. What are you trying to do? If you do want to slow down the video you need to do the same with audio if it is double system.

If you use Cinema Tools it just changes the metadata which changes the way FCP & quicktime plays the file.


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Robert Martin
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Nov 11, 2011 at 3:29:42 am

what is a double system?

Currently I have a 25fps app pro res 422 file of the completed short film.

the ultimate goal is to conform this HD file to 24fps, than down convert this new hd 24fps file using the mpeg2 dvd 90min best settings

Is there another work load you would prefer to avoid audio syncing and pitch issues?

I need help.


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Robert Martin
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Nov 11, 2011 at 3:32:40 am

what is a double system?

Currently I have a 25fps app pro res 422 file of the completed short film.

the ultimate goal is to conform this HD file to 24fps, than down convert this new HD 24fps file using the mpeg2 dvd 90min best settings

Is there another work load you would prefer to avoid audio syncing and pitch issues?

I need help.


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Michael Gissing
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Nov 11, 2011 at 4:06:13 am

Double system is where sound is recorded separately and synced. What you are doing requires that the sound is processed seperately and slowed down 4% with the pitch maintained. To do this you need to find a facility with MPEX3, Pitch N Time or iZotope software which can lengthen but keep correct pitch.

So Cinema Tools with the video and separate process on the sound. Yes it will make it slower and the duration will change.If that is OK then make the DVD after converting the video and audio in Compressor to m2v and ac3.

If you need the same duration, then convert the frame rate in Compressor. Software standards conversions are not fantastic and they take a long time. Turn frame controls on and change the frame rate, set rezise to best. This is an alternate approach that maintains duration and pitch.


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Robert Martin
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Nov 11, 2011 at 6:42:09 am

I am currently doing the conform process in compressor

QUICKTIME: APP PRO RES 422

Here are my settings for frame control:

Resize Filter- Best (statistical prediction)
Output Fields- Same as Source
Deinterlace- Best (motion compensated)

adaptive details box- checked
anti-alias & details levels dials- both at 0

Rate Conversion - Best (high quality motion comp)
Set duration to: 100% of source

Geometry
Frame size: 100% of Source

ARE THESE SETTINGS CORRECT TO KEEP THE AUDIO IN SYNC AND TO NOT CHANGE THE PITCH? WILL THE VIDEO DURATION BE THE SAME?

it says it's going to take 20hrs....wow


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Robert Martin
Re: Cinema Tools conform from 23.98 to 25fps - occasional audio sync problem
on Nov 12, 2011 at 5:50:31 am

I did the conform in Compressor and it worked PERFECTLY- no audio delay/syncing issues, no pitch changes, video of the duration stayed the same, and there is no need to de-interlace.

Victory.

oh by the way.... it took 20 hours! But at least it worked- take that PAL!


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