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  #1  
Old 05-31-2023, 09:23 AM
idris idris is offline
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Default Video sync stability

I've been doing some tests with audio/video sync, much in same way the Syncheck used to work - 1 frame of 1kHz tone concurrent with 1fr white flashes on a video screen.


I'm running my video output, via a Blackmagic PCI card in a Thunderbay expansion crate, and then via HDMI to a domestic grade Toshiba LCD screen.

I've started from an H264 (created for me by a video editor) and have placed audio sync pips on a mono PT track.



The results I'm getting are quite variable: with flashes/pips every 2 seconds the measured sync can vary by about a frame (max to min).



I'm interested to know whether there is something inherrently unstable about my PT and video hardware, whether the H264 is the weak link or whether it's my measurement ... or whether that's reasonably stable.



Any thoughts?
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  #2  
Old 05-31-2023, 09:59 AM
its2loud its2loud is offline
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Default Re: Video sync stability

H264 is most definitely your weakest link. Try testing with DNXHD or ProRes
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Old 06-02-2023, 02:35 AM
Frank Kruse Frank Kruse is offline
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Default Re: Video sync stability

Quote:
Originally Posted by idris View Post


The results I'm getting are quite variable: with flashes/pips every 2 seconds the measured sync can vary by about a frame (max to min).
Yes that's normal for a system that isn't genlocked. But using H264 doesn't help lowering the span either.

See here:

https://www.pro-tools-expert.com/pro...ools-explained

(BTW: the illustration in that article is missing an important connection: the sync signal going to the video hardware from the generator. Without it it won't work)

But with your hardware you won't be able to achieve 100% sync so you'll have to live with up to +- 1 frame of sync span for every time you hit play.
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Old 06-15-2023, 09:14 PM
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Vedat Vedat is offline
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Default Re: Video sync stability

Hi Idris,
If you have an iPhone you can use Catchin' Sync to test your system lag.
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Old 06-16-2023, 01:07 AM
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mgoorevich mgoorevich is offline
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Default Re: Video sync stability

I frankly still don't understand why people continue intentionally hurt themselves?

Its been said and written and white papered on every corner: use DNxHD36 or ProRes Proxy for most reliable sync.
An H.264 is a quick delivery codec and is NOT suited for work with Pro Tools. Its nature makes it drifting in unpredictable way even when trying to use it within the proper genlocked system.
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