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Patrick Kofler
out of sync
on Aug 10, 2010 at 2:29:17 pm

Hi to all,
I've been searching the cow, but couldn't find anything. Here's my problem:

I'm editing on an Apple MacPro with FinalCutStudio (last version), I have a BlackmagicDecklink HD Extreme card installed. For audio monitoring and recording I use a presonus firebox (firewire). My problem is that I can't get audio and video in sync. The firebox works with the core audio drivers, so no drivers to modify. I can change the latency in FCP. This changes the offset between audio and the fcp preview, but nothing happens with the monitor connected via sdi to the bmd card. Video and audio are always way out of sync.

Any help is greatly appreciated.

Thanks
Patrick



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Margus Voll
Re: out of sync
on Aug 10, 2010 at 9:24:28 pm

Hi.

Monitor out of BM card. The whole idea is to monitor from capture card.
It is not likely that you get FW port audio and BM card audio in sync ever.

This is really old problem from the beginning of times as computers were slow etc.
Audio and video good sync is made in capture card.

--

Margus

http://iconstudios.eu


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Patrick Kofler
Re: out of sync
on Aug 11, 2010 at 7:56:44 am

Yeah! That's probably the only thing which works, since I had this problem also with usb interfaces.

Thanks!
Patrick



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Kristian Lam
Re: out of sync
on Aug 12, 2010 at 1:36:57 am

Hi Patrick,

The reason this is happening is because the HD Extreme card is running off its own internal clock while your Firebox is also running on its own clock. You have video output and audio output both running on different clocks, hence the AV sync issues.

I checked the Firebox manual and noticed that is has the option to use the SPDIF input as the clock source. If you can somehow convert the AES output of the HD Extreme card to SPDIF and connect that to the SPDIF input of the Firebox, then set the Firebox to use that clock source, you might be able to then use it as the audio output source. No guarantees though but worth a shot.

regards

Kristian Lam
Blackmagic Design


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