The Canon 5Dmk2 is well known for causing issues with lots of equipment (monitors, splitters, etc.) because of its resolution change when switched from Live View to Recording mode. This behavior is also seen on the Canon 60D, T2i and 550D.
Teradek has introduced a novel feature in Cube's firmware called DSLR Monitoring Mode that handles this resolution change. Previous Cube firmware versions used a separate "Canon 5D" mode combined with the external hardware button on Cube.
- Connect the Canon's HDMI output directly to Cube's HDMI input
- In Cube's web menu go to Video Setup -> Device Settings and select Show Advanced Options
- Turn on DSLR Monitoring Mode; follow the instructions shown in the web page to finish placing Cube in this mode
- Once Cube reboots, you will be able to record at will and the Canon won't drop the signal to Cube
- The Canon's HDMI output should be directly connected to Cube's HDMI input for best results
- You can remove the Canon 5D's camera data from being shown on the HDMI output by pressing the Info button on the camera 3 times
- You can remove the Canon T2i's camera data from being shown on the HDMI output by pressing the Display button on the camera 2 times