We added setting dialog for BlackMagic devices. By default JustBroadcaster tries auto detect mode, but sometimes you should do it manually.
1) insert BMD as camera, move mouse over slot and click on icon as showed
2) JB opens dialogs which shows all modes for your device:
3) So you can select mode and press "Apply" button for test the mode. After selecting just press "Close" button.
Sometimes we were confused by BMD. For example "UltraStudio Mini Recorder" and Apple TV connected by HDMI.
Apple TV generates a signal as 720p60 but BMD works only as 720p59.94, and doesn't work in 720p60 mode. Same result we observed in BM MediaExpress software.