Strange audio behavior with DeckLink 4K SDI and OBS

[MaintSenat]

Hello everyone,

We're using OBS together with a DeckLink 4K SDI card to handle videoconferencing workflows, and we've been facing some recurring technical issues.

Our setup is relatively straightforward:

• We feed an SDI video signal into the DeckLink card
• We bring that input into OBS, and activate the Virtual Camera
• In parallel, we capture a Windows window in OBS and send it to a Blackmagic ATEM video switcher for mixing/output

For audio:

• We do not use OBS as the main audio source, since the DeckLink is configured in passthrough mode (the embedded SDI audio is forwarded to the SDI output).
• We connect that SDI output to an external audio console, which is used as the “microphone” source in our video calls (Zoom, Teams, etc.)
• However, in OBS, both the “Desktop Audio” and “Mic/Aux” devices are enabled and set to use the DeckLink device.

Problem:
For the past few weeks, whenever we try to run a videoconference or test, there's no audio output and nothing shows up on our audio console (no level activity, no sound in the call).

We've found a workaround, although it’s far from ideal:

1. Close any browser tab that is playing audio (YouTube, videoconference, etc.)
2. In OBS settings, set both “Desktop Audio” and “Mic/Aux” to “Disabled”
3. Close OBS completely
4. Reopen OBS
5. Go to settings and reassign DeckLink as the source for both “Desktop Audio” and “Mic/Aux”
6. Reopen the browser and test with a YouTube video to check for audio

Sometimes, this still doesn't fix it — in which case we need to restart the computer entirely between quitting and reopening OBS.

Technical details:

• DeckLink driver version: 14.5 (we had the same issue with version 14.2)
• OBS version: 31.0.3 (problem also occurred in OBS 30.x.x versions)

Has anyone run into a similar issue with audio routing or DeckLink passthrough in OBS?
Any help or suggestions would be greatly appreciated!

Thanks in advance,
Eliot