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Audio Sync Issues with Black Magic Decklink Studio

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Philip Barbour
Audio Sync Issues with Black Magic Decklink Studio
on Aug 7, 2012 at 2:11:02 pm

I am having all sorts of audio sync problems. I am using a Broadcast Pix Granite 1000 Video Switcher

http://www.broadcastpix.com/Products/Granite-1000.html

along with an Mackie Onyx audio board, and a Black Magic Decklink Studio 2 for video streaming. I'm using Adobe Flash Media Live Encoder along with Internap (CDN) to host my live video stream. From the Broadcast Pix to the Black Magic card, the sync looks fine. But when I do a test stream to Internap, the audio is anywhere from 1 second to 8 seconds ahead of the video. I do the test by watching the live stream from Internap on another computer. I added in a Rane AD22S Audio Delay unit, but I'm still getting these same, long delays.

I've been told by the Broadcast Pix people that a delay of more than a second sounds unusual. But I can't for the life of me figure out where the problem is. Any ideas??


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Chris Pearse
Re: Audio Sync Issues with Black Magic Decklink Studio
on Aug 9, 2012 at 7:04:40 am

Hi Philip,

I'm not sure where the audio delay problem is coming from. But from experience I have never known a DeckLink card to introduce an audio delay itself. Chances are the delay is being introduced either before or after the card.

The nature of the delay can give you at least an indication of where the delay is occurring. If it's a constant delay, for example if the delay is always 1 second off, and that delay doesn't change, its more likely a problem before the input into the card.

If however the audio is drifting out of sync over time, it's more than likely an encoding problem. Chances are, if the system cannot keep up with the video encoding, and frames are being skipped, the audio and video may start to drift apart. If possible I would suggest trying a different computer and see if it improves at all. I would also make sure that the CPU isn't being tied up with other processes, thus impacting it's encoding performance.

The only other thing I can think of is that if you were to use the DeckLink for video capture and a separate device like a sound card to capture audio. Again the two will drift because there's nothing to keep the two devices in sync. If you are capturing a separate audio source it will need to be captured by the DeckLink card as well to keep them synchronised.

Chris Pearse
Blackmagic Design


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