Avid Combustion sync issue


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I am color correcting in combustion and running into a sync issue - here is my workflow

film shot in 720 24P

edit in avid 23.976 timeline - 7 minute timeline

export QT reference file (should still be 23.976 at this point)

import into combustion and set project at 23.976 (it rounds off to 23.98)


export from combustion as Targa sequence to avoid recompression

import into avid

In the end the sync drifts by a couple frames at the end of the 7 minute timeline - I cant seem to figure out where this is occurring since QT reference is the original files and Targa should be frame for frame accurate.

Every test takes 10 hours to render so I wanted to see if anyone had any ideas

Instead of going from Avid to Combustion as a QT Ref, try exporting an image sequence out of Avid. See if that accounts for the drift.

Also, try a shorter sequence to test so you're not rendering 10 hours each time.

Hope that helps.
I recall using C3 a few years ago it and it also rounded off 23.976 to 23.98. I could not figure out why it did that, nor if it would make a difference to the output. I was having all sorts of problems though. That is another story.

You say a few frames out, sounds like might be 2-ish frames.

Here is some math on what you said:

mins x secs x fps = X
7 x 60 x 23.976 = 10069.92
7 x 60 x 23.98 = 10071.60
difference = 1.68 frames.

Applying above math, I think krestofre in previous thread suggested a possible solution, ie, export from Avid as an image sequence, because the 23.976 QT movie is being interpreted as 23.98 rounded is changing the clip length. Then export CC'd output from Combustion as an image sequence.

Not advice, good luck on the 10 hour groundhog day render....
thanks for the advice - i wish i could test on a shorter sequence but i need the length to nake the problem occur.

exporting images from avid is not only a long process but will require a lot of disc space -

why on earth would combustion round off frame rate when the standard is precision is 23.976
You could render at a lower resolution. That would save time and tell you if it fixes the sync issue before investing 10 hours in a render that might be worthless.

Also, exporting an image sequence from Avid will take a lot of disc space, but it shouldn't take too much time.
You need at least a thousand frames to test this since the whole .1% thing is a 1000/1001 issue.

In the latest shipping version of the product there is a console command for QT movies coming back in which is
Sorry to leave you hanging... for some reason the entry got posted before I was done. As I was saying, enter:

IgnoreQTRate true

in the console. It will ignore whatever frame rate is stamped in the QT file and import as a 1:1 (frame to frame) into the project type. You can have it stop doing this by typing same command with "false" instead of "true".

If file has audio, it will be dropped when using this command.

Michael - thanks for the tips but that wont help me - I think the issue is in combustion - it appears that the rounding of the frame rate in combustion is the issue so only an image for image in and out will(should) not effect the frame rate - I am going to test tonite
If you've still got an out of sync render you might as well try Michael's suggestion. It could save you some time , hard drive space, and headache. :)
I have avid 5.2 right now so I cant test - but I suspect it wouldnt help because coming out of avid I have a reference - then in combustion the frame rate is wrong so exported from combustion gives the wrong number of frames - so at one for one importing it wouldnt match up.

I am testing the image export and import to see if that is a workaround - and I have a ticket open with autodesk to see if there is a fix in combustion.

I just dont get how in the world autodesk can round the frame rate to 2 decimal places - thats just plain silly