There are several possibilities.
– Please make sure that the ribbon cable is connected properly
– Please use pivideo to check the status of the PiCapture card with “pivideo -q all -v”
– Make sure that the PiCapture blue LED is on indicating good video before attempting to start raspivid
– You can use a very simple raspivid command to make sure things are working: “raspivid -md 6 -o”
– If you have a regular Raspberry Pi camera you can use it to make sure your system is set up proplerly
– After you get one MMAL error, it is best to power-cycle the system to make sure that everything is reset before trying again. After you get one MMAL error you may continue to get them even if the issue that caused the first one is resolved.