Extract the values the step_done message.
MT safe.
| this |
A valid Message of type GST_MESSAGE_STEP_DONE. |
| format |
result location for the format |
| amount |
result location for the amount |
| rate |
result location for the rate |
| flush |
result location for the flush flag |
| intermediate |
result location for the intermediate flag |
| duration |
result location for the duration |
| eos |
result location for the EOS flag |