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Shifts in export every 4 seconds

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Grady Smith
Shifts in export every 4 seconds
on Nov 23, 2012 at 10:05:18 pm

hello,

Apple ProRes exported using Compressor to mpeg4 for youtube (Larry Jordans settings)

static medium shot.

When I view result in quicktime there is a slight shift (gamma or exposure or color) every 4 seconds.

It's like every 4 seconds it jumps to higher resolution then starts to degrade a bit then 4 seconds later jumps back to higher res. Its hard to notice except on brick background but definitely there.

Any thoughts?

Thanks so much!


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Michael Gissing
Re: Shifts in export every 4 seconds
on Nov 23, 2012 at 11:31:02 pm

Sounds like the key frame intervals for "I" frames is set too long. Try shortening it down. It will make the file bigger but less likely to suffer the delta frames degrading so much.


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Rafael Amador
Re: Shifts in export every 4 seconds
on Nov 24, 2012 at 2:52:36 am

As Michael say, is an issue with the K-Frames.
I saw his page and the still shows "Key-frames Interval:120".
That means that if you are dealing with 30fps stuff you get one key-frame every 4 seconds, and then the issue you are experimenting.

120 frames interval for Key-frames is ridiculous, and I can't understand why Mr Jordan is misleading everybody recommending that number. In fact he shouldn't be recommending any number, because nobody can knows which is the best number for key-frames Interval.
Think that in standard MPEG-2 for DVDs, the usual is a Key-frame every 15 frame for NTSC and every 12 frames for PAL. Setting a key-frame every 120 frames you ensure that you will get crap.
So, which is the best number for key-frames?
Check "Key-frames: AUTO", and let the application analyze the film and set the optimal key-frames number. This is why the "Multi-pass" compression is for.
rafael

http://www.nagavideo.com


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Grady Smith
Re: Shifts in export every 4 seconds
on Nov 24, 2012 at 11:41:36 am

Hi Rafael,
Still a problem. I adjusted the Key frames to 15 (using fcp 6 and dont see option for AUTO).
frame rate is 23.98.

Do you have settings for youtube you like?

Thanks


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Rafael Amador
Re: Shifts in export every 4 seconds
on Nov 24, 2012 at 1:07:48 pm

Having a deeper look to Larry Jordan workflow, I see even more problems.
Those MP4 only are "Isma Profile" MP4, so they don't allow to export H264/Mp4 that is a much higher quality option. Only allow to export an old fashioned Mp4 codec (QT.6 compatible).
So forget about that "Share" workflow, and use QT Pro for the MP4 compression.

Open your file with QT, select Mp4 and set it more or less like this:



Then, in the "Video Options", select Multipass.
Set the data rate according with the picture size.
Audio AAC 128Kbps (or better) and "Enable Streaming".
rafael

http://www.nagavideo.com


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Grady Smith
Re: Shifts in export every 4 seconds
on Nov 24, 2012 at 6:52:13 pm

Great! Thanks Rafael!


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