Decklink output does not function at higher than 1080p60

Operating System Info

Windows 11

Other OS

No response

OBS Studio Version

31.0.0

OBS Studio Version (Other)

No response

OBS Studio Log URL

https://obsproject.com/logs/zfDsU9rtYLAq8YPv

OBS Studio Crash Log URL

No response

Expected Behavior

When going into Tools > Decklink Output, selecting 2160p60 from the available options and pressing start, this should output a 2160p60 video over the selected SDI connection through the Decklink card.

Current Behavior

When selecting 2160p60 (or any resolution higher than 1080p60) the output fails to start. At best currently only a 1080p60 feed can be output via the Decklink.

Steps to Reproduce

1. Have a Blackmagic decklink card capable of 2160p60 output over SDI
2. Select output ioptions in Blackmagic Desktop Video to 2160p60
3. Attempt to output 2160p60 from Tools > Decklink Output
   ...

Anything else we should know?

I have confirmed this issue is present when using the Decklink 8K pro (original and G2 variants). The problem occurs both on the current Decklink software (14.4) and when downgrading the software to the last known stable SDK that was used in the OBS decklink output function (12.0) and any version of the software inbetween. This problem appears to be consistent with all Decklinks as reported on the forum going back the last few years.

I have confirmed the 2160p output is fully functional in Wirecast as well as in Blackmagics own software so the problem is localised to OBS.

Main indication is that this feature in OBS needs to be updated to the current Decklink SDK and possibly may need some updates to work with current versions of FFmpeg which could also be the source of the problem.

Start at the Tools > Decklink Output entry point and reproduce with a DeckLink 8K Pro at 2160p60, checking the OBS log. Trace the DeckLink SDK and FFmpeg interaction across the reported SDK versions; done means 2160p60 output starts successfully over the selected SDI connection.