In this example, the audio lags behind the video about 67 frames according to Premiere (it's really more like 67.5 frames). The tone should be audible only when the clapper bars are moving. At the end of this clip, I pause playback in the middle of the clapper bar movement so you can perceive the lag better.

http://www.filedropper.com/multicorder1-decklinkminirecorder11-01june2016-04-11-35am

Original clapper video file: http://www.filedropper.com/barsclapper

Where the playhead is in this image is where the video begins to move, which is where the corresponding audio tone should be as well.

Today I finally did the second new test with a long recording (2.5h) with the decklink may27 beta driver and all worked out well without any major problems with my setup.

Kind regards,
Jan

After you mentioned audio configuration problem, I checked my setup again and noticed Windows reactivated the default sound device as the blackmagic card in my system since the last time I rebooted the system (so I could move it from the rack). I disabled the blackmagic windows audio device as it was before trying the updated DLL file, and it has been working with no drift for a little over 24 hours. So, good news (I think). I will let it run another 24 hours just to be sure. It probably gets grumpy if Windows OS and vMix are directly trying to output to the blackmagic card at the same time...



Yes, for the purposes of capturing the problem for Martin to look at, I used a different (secondary) PC to capture the vMix SDI output from the primary computer. I attached it after Martin requested I record the problem, since I previously had only an SDI monitor attached to the vMix computer.

After my last message, I checked it a few hours later and was seeing the drift issue I was hoping not to encounter. Frustrated, I decided right then just to restore back to my initial Windows 7 disk image from back before I installed Windows 10 on this system to see what would happen. In the 48 hours since then, I have seen a remarkable and dramatic difference in the graphics rendering performance as well as the external output to the DeckLink card. Mind you, I have the exact same hardware situation as before, and the jittering I would still occasionally see after applying the patched DLL file is now completely, 100% gone from what I've seen the last 48 hours.

Why Windows 10 on this hardware seems to be so terrible performance-wise is a good question, but this system is running much better under Windows 7 with the patched DecklinkPlugin.dll Martin provided.